Biology MCAT Flashcards

Question

what are the functions of enzymes?

Answer 1

* Lower activation energy of a reaction * Increase the rate of the reaction * Do not affect the overall Δ G or Δ H of the reaction affect rate or kinetics affecting how quickly reaction reaches equilibrium * Are not changed or consumed in the course of the reaction * Picky catalyze single reaction in a class of reactions enzyme acts upon substrate, enzyme-substrate complex, active site location within enzyme where substrate held,

Answer 2

- substrate and enzyme active site don't fit together, once substrate present and ready to interact with active site, molecules find the induced form, transition state, more comfortable for both of them. Shape of active site becomes truly complementary only after substrate binds the enzyme, substrate of wrong type will not cause appropriate conformational shift in enzyme, active site no exposed and no reaction occurs

Answer 3

- no protein molecules, enzymes without cofactors are apoenzymes, containing them holoenzymes. Attached by weak noncovalent interactions to strong ones, tightly bound are prosthetic groups. Including metal ions and small organic groups/coenzymes.

Answer 4

cofactors, vitamins, coenzymes, concentrations, Enzyme-catalyzed reactions tend to double in rate for every 10° C increase in temperature until the optimum temperature is reached, this optimal pH is 7.4

Answer 5

Allosteric enzymes alternate between active and inactive form, inactive is incapable of carrying out enzymatic reaction, binding can include allosteric activators or inhibitors, causing a conformational shift in the protein. Activator will result in a shift that makes the active site more available for binding to the substrate. An inhibitor will make it less available. In addition to being able to alter the conformation of the protein, binding of activators or repressors may alter the affinity of the enzyme for its substrate.

Answer 6

feedback, reversible, irreversible.

Answer 7

the product may bind to an enzyme or enzymes that acted earlier in its biosynthetic pathway, thereby making the enzyme unavailable for other substrates to use

Answer 8

can be - competitive, noncompetitive, and uncompetitive

Answer 9

- made permanently unavailable, or enzyme permanently altered, acetylation and new proteins required to be made

Answer 10

digestive enzymes tightly controlled, enzymes secreted as inactive zymogens containing a catalytic active domain and regulatory domain, removed or altered to expose active site. Apoptotic enzymes exhibit similar regulation

Answer 11

Competitive inhibition occupancy of the active site, cannot access enzymatic binding sites if inhibitor in the way overcome by adding more substrate so substrate-to-inhibitor ratio is higher

Answer 12

Noncompetitive inhibition- inhibitor binding to an allosteric site instead of active inducing a change in enzyme conformation overcome by adding more substrate, once conformation altered no extra substrate will form an enzyme-substrate complex.

Answer 13

nitrogenous base, adenine, and ribose 2’ carbon bound to hydroxyl, 3 phosphate groups. Unfavorable negative charges, broken down to adenosine di-phosphate or monophosphate and pyro-phosphate 7kcal of energy.

Answer 14

nicotinamide adenine dinucleotide and flavin adenine dinucleotide coenzymes capable of accepting high energy electrons in glucose oxidation, come from hydride passed through ETC ATP generated using captured stored energy, carried to ETC on inner mitochondrial membrane liberated producing ATP

Answer 15

Input-six carbon glucose 2NAD+, output two molecules of three-carbon pyruvate, 2net ATP ADP+P=ATP substrate-level phosphorylation 2NADH

Answer 16

reduce pyruvate oxidize NADH 2carbons lost as CO2 when pyruvate built up lactic acid decrease pH and lactic acid able to be converted back by Cori cycle creating oxygen debt.

Answer 17

2ATP (from glycolysis), 2NADH (from glycolysis), 2NADH (from decarboxylation of pyruvate) • Pyruvate decarboxylation commits to aerobic respiration in presence of oxygen transported to mito matrix decarboxylated loses CO2, acetyl group bound to coenzyme-A acetyl-CoA, 2NADH

Answer 18

Combination of acetyl-CoA (2C) and oxaloacetate (4C) to generate citrate (6C). Through a series of eight reactions, two CO2 molecules are released, and oxaloacetate is regenerated6NADH (TCA cycle), 2FADH2 (TCA cycle), 2ATP (TCA cycle) each turn of cycle generates 1ATP via substrate-level-phosphorylation and a GTP intermediate generating high-energy electrons for each acetyl-CoA that enters 3NADH and 1FADH2 so total of 6NADH, 2FADH2, 4CO2 &2ATP to transport to inner mitochondrial membrane

Answer 19

line of carriers releasing free energy carriers of enzymes such as cytochromes undergo reversible redox reactions as electrons bind and release NADH dehydrogenase (complex I), next is the b-c1 complex (complex III), and the last is cytochrome oxidase (complex IV). First, NADH gives its electrons directly to FMN (flavin mononucleotide), which is part of complex I. Those electrons are then passed to carrier Q(ubiquinone). Carrier Q is a small hydrophobic molecule, not an enzyme (protein) like its neighbors. Carrier Q passes the electrons on to complex III, which donates them to complex IV. Oxygen takes the electrons from cytochrome a3, a protein in complex IV, along with two protons to make water. The energy from each NADH generates three ATP molecules. FADH2 generates 2 ATP, electrons given to complex II, succinate-Q oxidoreductase. Complex II gives those electrons to carrier Q, and the rest of the pathway is the same as NADH. FADH2's high-energy electrons travel a shorter distance to get to oxygen, and therefore, less energy is extracted from them. Production of energy couples energy drop to phosphorylation of ADP, reduced carriers give up electrons free protons passed into mito matrix accumulating, The electron transport chain then pumps these ions out of the matrix into the intermembrane space at each of the major protein complexes. The accumulation of H+ in the intermembrane space makes it both positively charged and acidic. the electrochemical gradient drives H+ passively back across the inner mitochondrial membrane into the mitochondrial matrix. This is known as the proton-motive force and the ATP synthases H+ ions energy released phosphorylation of ADP oxidative phosphorylation

Answer 20

glucose (monosaccharide, glycogen converted to glucose-6-phosphate, an intermediate), fats (adipose as triglycerides, 3long-chain fatty acid esterified to glycerol-3C to PGAL; fatty acids activated in cytoplasm process of ATP transported to mito matrix to beta-oxidation acetyl-CoA generated creating NADH and FADH2 per 100ATP/fat molecule), proteins amino removal by transaminases creating alpha-keto acids converting into acetyl-CoA

Answer 21

milk-producing mammary glands, three bones in the middle ear and one in the lower jaw, fur or hair, heterodont dentition (different kinds of teeth), and both sebaceous (oil-producing) and sudoriferous (sweat) glands.

Answer 22

animals encase their developing embryos within hard-shelled amniotic eggs and lay them to be hatched,

Answer 23

create organelles for energy and protein production (mitochondria, ribosomes, and endoplasmic reticulum

Answer 24

two identical chromatids at centromere ploidy doesn't change even though number of chromatids doubled containing twice as much DNA,

Answer 25

Prophase: Chromosomes condense formerly chromatin; spindles form of centrioles and centrosome spindle fibers connection asters nuclear membrane dissolving nucleoli less distinct and disappear, kinetochores appear at centromere;

Answer 26

Metaphase: Chromosomes align, opposite poles;

Answer 27

Anaphase: Sister chromatids separate, centromere’s split each chromatid own sister chromatids separate chromatids pulled toward opposite poles by shortening kinetochores

Answer 28

Telophase: New nuclear membranes form. Spindle apparatus disappears, nuclear membrane reforms around each set of chromosomes, nucleoli reappear, and chromosomes uncoil resuming interphase form complete copy of identical genome to original

Answer 29

binary fission, budding, regeneration, parthenogenesis

Answer 30

prokaryotes single circular DNA molecule attaches to cell membrane or duplicates when cell grows in size, invaginating cell membrane and wall pinching inward two equal daughter cells,

Answer 31

equal replication/unequal cytokinesis less cytoplasm, immediately break off or stay attached to parent until it grows to full size, hydra/ yeast (eukaryotes)

Answer 32

lizards, annelid worms, sea stars as long as central disk in tact,

Answer 33

adult organism develops from unfertilized egg (bees and ants) produce male,

Answer 34

homologous intertwine in a process called synapsis with a Tetrad- chromatids homologous chromosomes break at point of synapsis, chiasma exchange equivalent pieces of DNA called crossing altered but structurally complete set of genes sister chromatids no longer identical unlink linked genes, increasing variety of genetic combination produced via gametogenesis, recombination among chromosomes resulting in increased genetic diversity within species.

Answer 35

homologous pairs separate pulled to opposite poles of cell, disjunction each chromosome paternal origin separates from maternal distribution of two intermediate daughter cells is random with each having a unique pool of alleles with genes coding for alternative forms of given trait from random mixture of maternal and paternal

Answer 36

nuclear membrane forms around nucleus, haploid, 46 chromatids dividing by cytokinesis possible interkinesis in between

Answer 37

Homologous pairs line up. •An endonuclease nicks a single strand of DNA on each homolog at the same place. •The homologs exchange strands and are ligated together forming the Holliday Structure. •Branch migration can occur, incorporating a portion of the opposite strand into each molecule. •Cleavage occurs: If the same strands are cleaved the original chromosomes are reformed. If the opposite strands are cleaved then recombinant chromosomes result. Genes close together on chromosome have low chance of recombining=inherited together

Answer 38

gonads in testes; seminiferous tubules (sperm production nourished by Sertoli cells) and interstitial cells (cells of Leydig) secrete testosterone and androgens, located in scrotum maintaining temp 2-4oC lower than body sperm passed to epididymis, gain flagellum and are stored until ejaculation, passing through ejaculatory duct and urethra. Sperm passed through reproductive tract, mixed with seminal fluid produced by seminal vesicles (fructose for nourishment), prostate gland (mildly alkaline properties), and bulbourethral gland creating semen.

Answer 39

formation of haploid sperm occurs in seminiferous tubules, diploid stem cells- spermatogonia, replicate to form primary spermatocytes… head (containing genetic material/acrosome Golgi apparatus penetrate ovum), midpiece (generate energy from fructose for motility mitochondria), flagellum, tail (motility) 3 million per day

Answer 40

* Spermatogenesis, 4 functional sperm * spermatogonia (2n) * 1° spermatocytes (2n) * meiosis I * 2° spermatocytes (n) * meiosis II * spermatids (n) * maturation * spermatozoa (n)

Answer 41

* Seminiferous tubules * Epididymis * Vas deferens * Ejaculatory duct (Nothing) * Urethra * Penis

Answer 42

menopause- ovaries less sensitive to stimulating hormones FSH, LH with increases in these because no estrogen and progesterone feedback.

Answer 43

one egg released to peritoneal sac lining abdominal cavity moving into fallopian tube, oviduct connected to muscular uterus, lower end of cervix connecting to vaginal canal external cavity known as vulva

Answer 44

oocytes 2n frozen in prophase I then undergo meiosis I producing secondary oocyte and polar body, unequal cytokinesis and then frozen in metaphase II does not complete remainder of meiosis II until fertilization occurs.

Answer 45

Sperm cells secrete acrosomal enzymes to digest corona radiate and penetrate zona pellucida, forms acrosomal apparatus extending and penetrating cell membranes for the nucleus to freely enter the ovum not a secondary oocyte, ovum undergoes cortical reaction, calcium ions released into cytoplasm forming fertilization membrane increasing metabolic rate of ovum

Answer 46

• Ultrasonography is performed by placing a probe that emits high-frequency sound waves near the tissue to be examined. The probe transduces a photo onto a computer screen, which can be measured to determine gestational age, screen for multiple pregnancies or anomalies, and identify the baby's sex.

Answer 47

several rounds of mitosis occur, total size of embryo stays same increasing nuclear to cytoplasmic ration and surface area to volume ratio, increasing area for gas and nutrient diffusion relative to overall volume creating indeterminate (cells that can still develop into complete organisms) and determinate (committed to differentiating)

Answer 48

at 32,60, 72 hours post-fertilization 8 cell reached uterus

Answer 49

solid mass of cells

Answer 50

morula, undergoes blastulation or hollowing out to form blastula

Answer 51

is a hollow ball of cells with a fluid--filled inner cavity called the blastocoel outer ball of cells trophoblast gives rise to the chorion and placenta, and an inner ell mass of migrating cells which protrudes into blastocoel that gives rise to organism

Answer 52

when a blastula implants outside of the unterus, usually fallopian tubes inviable and aborts, rupture etc

Answer 53

after 5-8 days in blastula stage, embryo settles into uternine walls or endometrium

Answer 54

steroid hormone progesterone promoting proliferation of endometrial mucosal layer to implant, embryonic cells secrete enzymes that burrow into endometrial lining forming maternal circulation for nutrient and gas exchange, proteolytic enzymes allowing the embryo to settle into uterine wall generating placenta allowing for gas and nutrient exchange with endometrium

Answer 55

• Deuterostomes starts with deu, which sounds like duo, meaning two. Thus, in deuterostomes, the blastopore develops into the anus, associated with “ number two.” Proto– means before,

Answer 56

invagination of blastula, cell continues moving toward invagination resulting in elimination of blastocoel inner cell layer-endoderm. Migration in forming mesoderm . •Outer cell layer-ectoderm cavity created by deep invagination archenteron is area developing into gut, opening is known as blastopore

Answer 57

“ attracto” -derm. These are systems and organs that attract us to other people: their looks, their eyes, and their smarts. — integument (including the epidermis, hair, nails, epithelium of the nose, mouth, and anal canal), lens of the eye, and the nervous system — integument (including the epidermis, hair, nails, epithelium of the nose, mouth, and anal canal), lens of the eye, and the nervous system

Answer 58

The mesoderm is the “ means” -o-derm. This is how we get from place to place in the world, and how constituents get from place to place in the body. Bone, muscle, heart, and blood vessels all allow us to do this musculoskeletal system, circulatory system, excretory system, gonads, muscular and connective tissue coats of the digestive and respiratory systems

Answer 59

the endoderm is easy to remember because it gives rise to the “ endernal” organs; these include parts of the long tube that runs from the mouth to the anus (digestive tract) and the organs attached to it (accessory organs of digestion). The endodermal layer also gives rise to the lungs. epithelial linings of digestive and respiratory tracts (lungs, too) and parts of the liver (peritoneum external to the gut sac), pancreas, thyroid, bladder, and distal urinary and reproductive tracts

Answer 60

outpocketings from the brains optic vesicles grow out and touch the ectoderm inducing it to form lens and lens induces optic cup to form inducing the lens to develop into cornea and lens

Answer 61

cells are induced to migrate inward a rod of mesodermal cells of notochord forming along the long axis of the organism cells induce a group of ectodermal cells to slide inward to neural fold, surrounding a neural groove. Neural fold grow toward one another until fusing into a neural tube, giving rise to the central nervous system. The tip of each neural fold are neural crest cells which migrate outward to form peripheral nervous system, including sensory ganglia, autonomic ganglia, adrenal medulla, and Schwann cells ectodermal cells migrating over neural tube and crests to cover rudimentary nervous system.

Answer 62

most respiration occurs across the placenta and umbilical cord

Answer 63

It forms from the extra-embryonic membrane,

Answer 64

The trophoblast cells which the placenta develops form the chorion which has both added levels of protection

Answer 65

an extra-embryonic membrane that is surrounded by the amnion

Answer 66

(thin, tough membrane with amniotic fluid serving as a shock absorber in pregnancy and labor

Answer 67

inside the chorion outside of the amnion to provide nutrition and the site of early blood vessel development.

Answer 68

Placenta allows for close proximity o fetal and maternal bloodstreams diffusion can occur between them, nutrient, gas, and waste exchanges there are no mixing and different blood types. Simplest movement is diffusion how water, glucose, amino acids, and inorganic salts transferred with diffusion requiring a gradient. higher Oxygen in maternal blood than in fetal blood. fetal blood cells are equipped with fetal hemoglobin(Hb-F), which exhibits a greater affinity for oxygen than does maternal (adult) hemoglobin, known as Hb-A.

Answer 69

release progesterone, estrogen, and human chorionic gonadotropin. Immune protection- fetus immunologically weak foreign particles and bacteria too large to cross-placental barrier by diffusion, viruses, alcohol, and toxins are not. Placental producing progesterone, estrogen, and human chorionic gonadotropin (hCG).

Answer 70

connects right and left atria blood entering right atrium from superior vena cava flowing into left atrium instead of right ventricle and pumped out of aorta into systemic circulation by pressure differential. Right atrium blood traveling spontaneously down pressure gradient reversed in adults closed after birth for adult heart to function properly. he valve separating the right atrium and ventricle isn't closed shut, so not all blood will be immediately sent to the left side

Answer 71

The ductus arteriosus is present to shunt leftover blood from the pulmonary artery to the aorta bypassing the pulmonary veins. The pressure in the right fetal heart is higher than that in the left. If it doesn't close and stays open after birth will turn blue bypassing lungs and mixing blood

Answer 72

bypasses the liver and connects the umbilical vein to the inferior vena cava carrying oxygenated blood to the fetus. although the liver is underdeveloped and not able to detox, store sugar or balance metabolites.

Answer 73

major organs develop, heart beats at 22 days, soon the eyes, gonads, limbs, and liver start to form. 5 weeks, embryo 40mm and 6 week grown to 15mm. cartilaginous skeleton harden into bone by week 7. Eight weeks most of organs formed, brain fairly developed and embryo is fetus with fetus 9cm long.

Answer 74

fetus undergoes growth moving around in amniotic fluid, with human face appearance and fingers and toes elongated measuring the total fetus as 30-36cm.

Answer 75

7+8 months continued rapid growth and further brain development. 9 months antibodies transported by highly selective active transport form the mother to fetus protection against foreign matter with the growth rate slowing and fetus becoming less active less room to move about.

Answer 76

rhythmic contractions of uterine smooth muscle, coordinated by prostaglandins and the peptide hormone oxytocin. birth consists of three basic phases. First, the cervix thins out, and the amniotic sac ruptures, which is commonly known as the water breaking. Next, strong uterine contractions result in the birth of the fetus. Finally, the placenta and umbilical cord are expelled. These are often referred to as afterbirth.

Answer 77

Baby breathes air, no longer needing fetal hemoglobin to extract oxygen from mother’s blood. Infant begins producing producing adult hemoglobin right way, because breathing begins resistance in pulmonary vessels decrease causing an increase in blood flow through long and normal blood circulation closing foarmen ovale and ductus arteriosus and ductus venosus constrict with pressure in left atrium increasing. When blood flow through umbilical cord stops blood pressure in infererior vena cava decreases causing a decrease in pressure of righ atrium

Answer 78

Genotype is the actual allelic distribution of genes in an organism

Answer 79

phenotype is the outward appearance of an organism and depends on the genotype

Answer 80

offspring have the same traits as parents

Answer 81

* 1. Genes exist in alternative forms (alleles). * 2. An organism has two alleles for each gene, one inherited from each parent. * 3. The two alleles segregate during meiosis, resulting in gametes that carry only one allele for any inherited trait. * 4. If two alleles in an individual organism are different, only one will be fully expressed, and the other will be silent. The expressed allele is said to be dominate, the silent allele recessive.

Answer 82

di-hybrid cross- each gene’s inheritance or assortment is independent of or unrelated to the inheritance of other genes for genes unlinked. Linked genes inheritance of one does affect the other

Answer 83

diploid species having homologous pairs of chromosomes one allele located on one chromosome other allele is located on paired (homologous) chromosome.

Answer 84

allows for greater genetic diversity in offspring daughter DNA strand held to parent strand at centromere, lining up during metaphase I and separating during anaphase I with reductional division due to haploid cells homologous pairs separating even though remaining attached

Answer 85

recombinant phenotypes linkage be weak when number of recombinant in F1 progeny approaches number expected from independent assortment, tightly linked genes recombine at frequency of close percent, weakly linked genes recombine at frequencies approaching 50% leads to recombination physical exchange of DNA between homologous chromosomes paired during meiosis

Answer 86

• Crossing over- genes that initially linked may be unlinked by crossing over, combination occurred between sisters chromatid, no change in linkage frequency would be observed because sister chromatid are genetically identical

Answer 87

neither allele is dominant resulting in a phenotype that is a mixture of the two parental phenotypes.

Answer 88

two allele in which multiple coding alleles for a gene, when present they are expressed simultaneously with the resulting phenotype not an intermediate of the two of incomplete with the complete expression of both phenotypes

Answer 89

number of individuals in the population carrying the allele who actually express the phenotype, some people do not express their genotype or have disease

Answer 90

varying expression of disease symptoms despite identical genotypes with a range of phenotypes

Answer 91

caused by nondisjunction of chromosomes and sister chromatids missing 1 or 2 of the extra or lack thereof of genetic material

Answer 92

Females may be born with a single X chromosome (XO); they are known as Turner syndrome females and are characterized by short stature, sterility, and few to no secondary female sexual characteristics. Females may also be born with an extra X chromosome (XXX) and are referred to as metafemales or superfemales. They may be mentally retarded and sterile. Males are also subject to extra sex chromosomes. An XXY genotype (Klinefelter male) results in a tall male who develops breasts and undescended testes and is also usually sterile. Finally, some males may have an XYY genotype and may be taller than the average male. Generally, the presence of extra sex chromosomes is not incompatible with life

Answer 93

consisting of skull, vertebral column, and ribcage providing basic central framework for body

Answer 94

consisting of arms, legs, and pelvic and pectoral girdles attached to axial skeleton for stability

Answer 95

1) protection of internal organs and support body 2) movement with muscular system 3) maintenance of calcium ion homeostasis 4) formation of blood cells in bone arrow

Answer 96

firm but elastic matrix chondrin secreted by chondrocytes

Answer 97

external ear, nose, walls of larynx and trachea, and joints

Answer 98

cartilage relatively avascular without blood and lymph vessels not innervated, chondro- cartilage. Nonarticular cartilage can grow and repair throughout life and degradation of this cartilage, leads to arthritis because a lack of cartilage in joints lead bones to rub directly against one another

Answer 99

bone- comprised of connective tissue derived from embryonic mesoderm

Answer 100

bone’s characteristic strength derived from compact bone, which is strong, hard and dense. which are cartilaginous structures site of longitudinal growth with a fibrous sheath

Answer 101

less dense lattice structure consists of bony spicules (points) as trabeculae in long bone, cavities are filled with bone marrow

Answer 102

marrow is the central cavity of bones, can be either red (filled with hematopoietic stem cells responsible for generation of all cells in our blood, form blood and immune cells including lymphocytes, monocytes, leukocytes, B cells and T cells ) or yellow (composed primarily of fat and stores fatand is relatively inactive)

Answer 103

206, 100 bones in feet and hands

Answer 104

have long bones, characterized by cylindrical shifts, Peripheries of these two bones are composed of compact bone, with differing internal cores, separating epiphysis and diaphysis by epiphyseal plate

Answer 105

long bones with cylindrical shafts (full of marrow surrounded by compact bone) and dilated end

Answer 106

the dilated ends of long bonds (have a spongy bone core inside compact bone sheath for more effective dispersion of force at joints)

Answer 107

fibrous sheath, surrounds long bone to protect it and serve as site for muscle attachment. some cells are capable of differentiating into bone-forming cells necessary for bone growth and repair

Answer 108

the peripheries of both are composed of compact bones with different internal cores

Answer 109

the epiphyseal plate separates the two structure by a cartilaginous structure which is the site of longitudinal growth.

Answer 110

comes from the bone matrix, which has organic (collagen, glycoproteins, and other peptides) and inorganic components,(include calcium, phosphate, and hydroxide ions, which harden to form hydroxyapatite crystals, sodium, magnesium, and potassium stored in bones

Answer 111

requiring uniform distribution of inorganic material

Answer 112

ordered into structural units, osteons or Haversian systems, with each osteons encircling a central microscopic channel known as Haversian canal which runs the length of the bone, surrounded by concentric circles of bony matrix from lamellae which is spaced out. with the canals containing blood vessels, nerve fibers, and lymph that keep the bone in peak condition

Answer 113

house mature bone cells, or osteocytes which are involved in bone maintenance with osteoblasts become surrounded by matrix.

Answer 114

each of the lacunae is interconnected by canaliculi, little canals that allow for exchange of nutrients and wastes between them and aversion canals.

Answer 115

bodies created by the hardening of cartilage. process is known as endochondral ossification, and responsible for the formation of long bones in the body. or intra-membranous ossification, where undifferentiated embryonic connective tissue (mesenchymal tissue) is transformed into, and replaced by, bone via skull.

Answer 116

osteoblasts produce collagen when mineralized bone forms and builds bone that are regulated by parathyroid. use calcium and phosphate to reform bones obtained from the blood by osteoblasted.

Answer 117

destroy or resorb bone contributing to the constant maintenance of bone. when the bone resorption or breakdown occurs ions are released into bloodstream

Answer 118

endocrine hormones parathyroid hormone raising blood calcium levels by stimulating release from bones and calcitonin lowering blood calcium inhibiting release from bone. Calcitonin tones down blood calcium. Vitman D helps with the secretion of bone matrix.

Answer 119

they are made of connective tissue and can be either movable which work like door hinges and allow for bones to shift relative to one another allowing for limited flexibility which are strengthened by ligaments or pieces of fibrous tissue that connect bones to one another and consist of a synovial capsule enclosing the actual joint cavity (articular cavity, with synovial fluid used to ease the movement of one structure over the other. the articular cartilage coats the articular surfaces of the bone so that impact is restricted to the lubricated cartilage

Answer 120

muscles controlled by the somatic nervous system, with the basic contractile unit of a muscle called the sarcomere and are put end to end to create myofibrils sarcomeres are made up of thick and thin filaments, with the thick filaments organized into bundles of myosin, whereas the thin filaments are made up of actin, troponin and tropomyosin

Answer 121

•Z-lines define the boundaries of each sarcomere (and are responsible for the striated nature of skeletal and cardiac muscles). The M-line runs down the center of the sarcomere. The I-band is the region containing exclusively thin filaments, whereas the H-zone exclusively contains thick filaments. letter I is thinner and the letter H thicker to help us remember which filament type each refers to (actin or myosin). The A-band contains the thick filaments in their entirety, including any overlap with thin filaments. During contraction, the H-zone, I-band, and distance between Z-lines all become smaller, whereas the A-band's size remains constant. • Myosin, the “ thicker” word, is composed of thick filament. Actin, the “ thinner” word, is composed of thin filament. We can also remember that troponin and tropomyosin, both of which start with T, are associated with acTin, rather than myosin.

Answer 122

they are made up by multinucleate cells fusion of several embryo uninucleate cells at periphery of cell , walk skeletal muscle innervated by somatic nervous system as voluntary, muscles intricately made up of repeating units, skeletal muscle striated in stripes due to alignment of Z lines with increased density relative to other structures and are striated with strong forceful contractions. Consists of red (slow twitch, high myoglobin content and primarily derive energy aerobically similar to hemoglobin consists of single polypeptide chain binding oxygen more tightly to hemoglobin, mitochondria rich derive energy aerobically) and white fibers, fast twitch anaerobic and have less myoglobin mitochondria poor do not use ETC, contract more rapidly and easier to fatigue) •Somatic innervation •Ca2+ required for contraction

Answer 123

smooth has 1 nucleus per cell and is non striated with smooth continuous contractions(responsible for involuntary action controlled by the involuntary autonomic nervous system, found in digestive tract, bladder, uterus, blood vessel walls, and other location. exhibits myogenic activity without nervous system input, responding to nervous input does not require external signals to contract, have centrally placed nuclei, contain actin and myosin and are not organized in a striated fashion, contracting in same way and capable of longer and more sustained contractions) with Ca2+ required for contraction. can contract without nervous input, myogenic activity

Answer 124

and cardiac- characteristics conglomerate of properties of smooth and skeletal muscle, calcium required for contraction, may also exhibit myogenic activity. structure is striated with 1-2 nuclei per cell, controlled by the involuntary or autonomic nervous system through the use of strong forceful contractrions

Answer 125

The nervous system sends signal via the motor neuron reaching nerve terminal where the release of the neurotransmitter synapse results in the contraction of a muscle due to the binding of neurotransmitters to its receptor on the muscle called the neuromuscular junction. If enough of the neurotransmitter, acetylcholine binds to the muscle the cell will become depolarized (action potential generation) and the sarcolemma, or cell membrane's permeability will increase which is capable of propagating an action potential, with a system of T-tubules connected to the plasma membrane and oriented perpendicular to the myofibrils allowing ions to flow

Answer 126

the action potential generated at the neuromuscular junction was conducted along the sarcolemma and T-tubule system which is then transmitted into the muscle fiber causing a release of calcium ions from the sarcoplasmic reticulum, which is endoplasmic reticulum and outside of that is the cytopol sarcoplasm in the SR the calcium will be released and will bind to troponin, causing tropomyosin to shift and expose the myosin-binding sites on actin passing through the tropomyosin shift, or the myosin binding sites allowing us to get to our destination of the actin and myosin binding that results in movement.

Answer 127

actin and myosin binding resulting in movement, the free globular heads of the myosin molecules move toward and bind on the exposed sites of the actin, the newly formed bridges allows the myosin to pull on actin, drawing the thin filaments to the center of the H zone shortening the sarcomere, ATPase activity in the myosin heads provides the energy for power and results in the dissociation of actin from the myosin. With the myosin resetting itself by binding another molecule of ATP and freely binds to another actin molecule

Answer 128

When the sarcoplasmic reticulum is not stimulated the calcium levels fall, new ATP molecule binds after ATP is hydrolyzed with the dissociation of myosin form the thin filament, with the sarcomere returning to the original width, without the calcium the myosin-binding sites are covered by tropomyosin preventing contraction,

Answer 129

all or nothing response, stimuli must reach threshold value, strength not adjusted muscles control overall force by the number of fibers they recruit to respond. Maximal response occurs when all fibers are stimulated to contract simultaneously.

Answer 130

Atp no longer produced, myosin heads cannot detach from actin and not allowing muscles to relax so stuck that way

Answer 131

response of a single muscle fiber to a brief stimulus at or above the threshold, consisting of a latent period (time between reaching threshold and onset of contraction) during this time that the action potential spreads along the muscle and allows for Ca2+ to be released from the SR. After this period, the muscle will be unresponsive to stimuli. This is known as the refractory period, of which there are two types: absolute and relative. During the absolute refractory period, no amount of stimulus will generate a response because the muscle is restoring its resting potential. During the relative period, the muscle can still be activated, but a higher than normal stimulus is required.

Answer 132

When muscles are exposed to frequent and prolonged stimulation they will not have time to relax and so the contractions begin to combine, becoming stronger than a simple muscle twitchand more prolonged with a frequency of summation, so frequent that is doesn't relax such as tetanus prolonged tetanus creates muscle fatigue.

Answer 133

fatty acids, glycogen, and glucose. With the energy derived from high-energy creatine phosphate storing the energy by transferring phosphate from ATP to creatine, and reversed in muscle use more advantageous to have stock of it

Answer 134

myoglobin is found in muscle cells, it binds oxygen and holds onto it more tightly than hemoglobin, and the reserves are used up by aerobic means before anaerobic to from lactic acid from fermentation which can be converted back into energy-producing intermediates once sufficient levels of oxygen become available. This process occurs in the liver and is known as the Cori cycle

Answer 135

Binds and supports other tissues, contains sparsely scattered populations of cells contained in an amorphous ground substance that may be liquid, jellylike or solid. and loose connective tissue is found throughout the body attaching epithelium to underlying tissue and packing material holding organs in place

Answer 136

• collagenous fibers, which are composed of collagen and have great tensile strength (think nails and screws); elastic fibers, which are composed of elastin and endow connective tissue with resilience; and reticular fibers, which are branched, tightly woven fibers that join connective tissue to adjoining tissue. There are two major cell types in loose connective tissue: fibroblasts, which secrete substances that are components of extracellular fibers, and macrophages, which engulf bacteria and dead cells via phagocytosis.

Answer 137

connective tissue with a high proportion of collagenous fibers. The fibers are organized into parallel bundles that give the fibers great tensile strength, Dense connective tissue forms tendons, which attach muscle to bone, and ligaments, which hold bones together at the joints.

Answer 138

The end of the muscle attached to the stationary bone is called the origin; in limb muscles, it corresponds to the proximal end. The end of the muscle attached to the bone that moves during contraction is called the insertion; in limb muscles, the insertion corresponds to the distal end. Muscles Working in antagonistic pairs- one relaxes while other contracts. muscles don't have an elongation function; the contraction of the antagonistic muscle will lengthen the paired muscle (e.g., biceps contracts, triceps elongates). Note that elongation is different from relaxation. All muscles can relax when the myosin heads and actin are unbound. There are also synergistic muscles, which assist the principal muscles during movement. A flexor muscle will contract to decrease the angle of a joint (e.g., the biceps will flex the elbow joint), whereas an extensor muscle will contract to straighten the joint (e.g., the action of the triceps on the elbow). An abductor moves a part of the body away from the body's midline; an adductor moves a part of the body toward the midline.

Answer 139

mechanical digestion is mastication, with chemical digestion in the mouth including salivary amylase or ptyalin and lipase. peptide bond of proteins or the glycosidic bond of starches

Answer 140

body cavities (e.g., nasal cavities, inner eyelids, mouth, gastrointestinal tract), these epithelia are known as mucous membranes. Our skin and other epithelial linings help us by preventing fluid loss as well as by allowing for selective absorption of materials that our bodies require, especially in the digestive tract. Bound to connective tissue layer or basement membrane giving stability in digestive tract epithelium attached to basement membrane replaced every few days because of harsh conditions (ex. Corrosive environments or extreme temperatures) The epithelium of the skin is derived from ectoderm; the epithelium of blood vessels is derived from mesoderm; the epithelium of the GI tract is derived from endoderm.

Answer 141

simple refers to one layer, stratified means multiple layers, and pseudostratified means that it looks like multiple layers due to differences in cell height but is one. Turning to shape, cells may be cuboidal- sugar cube, columnar- columns, and squamous-scale-like.

Answer 142

The cavity leading from the mouth and nose to the esophagus, with the epiglottis which folds down and covers the trachea during swallowing

Answer 143

•muscular tube starts out with striated muscle and transitions into smooth muscle in thorax, esophagus involuntary control through autonomic nervous system, upper third of esophagus, striated skeletal muscle, under voluntary motor control, peristalsis continuation of that muscular contraction involuntary. Swallow initiated in muscles of oropharynx continues into smooth muscles of esophagus as progressive contractions; with contraction forming waves continuing throughout gastrointestinal tract and push food through tube. The bolus doesn't just fall down the esophagus via a passive reliance on gravity; rather, it is actively pushed, propelled, and squeezed from one region of the digestive tract to the next. As the bolus approaches the stomach, a muscular ring known as the lower esophageal sphincter (cardiac sphincter) opens to allow the passage of food.

Answer 144

capacity of 2 liters and is muscular, located on left side of upper abdomen under diaphragm, using acid and enzymes to digest food in a fairly harsh environment with thick mucosa, protecting stomach from auto digestion and harshly acidic (pH2) and proteolytic environment of stomach, containing gastric glands (respond to signals from the brain which are activated by the sight, taste, and smell of food, composed of mucous cells, chief cells, and parietal cells), and pyloric glands (glands secrete gastrin, hormone) gastrin induces stomach to secrete more HCl and mix contents of stomach, produces acidic, semifluid mixture chime. Combined mechanical and chemical digestive activities of stomach result in significant increase in surface of food particles so when chime reaches intestines, absorption of nutrients from it maximized. primarily digestion and not absorption although alcohol and aspirin can be absorbed. With gastric juice as a combination of

Answer 145

chief cells of digestion in stomach, secreting pepsinogen or zymogen form of proteolytic enzyme pepsin. Pepsin digests proteins by cleaving peptide bonds near aromatic amino acids, resulting in short polypeptide fragments. Parietal cells secrete hydrochloric acid (HCl), a strong acid that serves many purposes. zymogens activated by HCL which kills most harmful bacteria.

Answer 146

* H+ (kills microbes, denatures proteins, converts pepsinogen into pepsin) * Pepsinogen (pepsin partially digests proteins) * Mucus (protects mucosa) * Bicarbonate (protects mucosa) * Water (dissolves and dilutes ingested material) * Intrinsic Factor (required for normal absorption of vitamin B12)

Answer 147

the small intestine has maximized surface area valuable for absorption, maximizing surface area by villi with each covered by microvilli, • This has the overall effect of increasing the relative surface area to over 300 square meters, thereby dramatically increasing the absorptive capabilities of the small intestine. Bacteria reside throughout the small intestine and assist with its digestive and absorptive functions. Over 400 species of bacteria reside in the gut!food leaves the stomach through the pyloric sphincter, and enters the duodenum of the small intestine. • Carbohydrates & amino acids, absorbed in small intestine capillaries, enter circulation via hepatic portal system. Fats- absorbed into lacteals in small intestine, bypassing hepatic portal circulation enters systemic circulation via thoracic duct,

Answer 148

As chyme enters the duodenum, it triggers the release of hormones that lead to secretions from the small intestine itself, as well as from the accessory organs of digestion.

Answer 149

Work at ph8.5, neutralizing acid chyme, including pancreatic amylase, ( which breaks down large polysaccharides into disaccharides) the pancreatic peptidases (trypsinogen, chymotrypsinogen, elastinogen, and carbonxypeptidase) which are released in the zymogen form and are responsible for protein digestion. The pancreas also secretes lipase breaking down fats to free fatty acids with the enterokinase produced by the small intestine as the master switch activating trypsinogen to trypsin, activate the other zymogens and peptidases

Answer 150

complex fluid made up of bile salts, bile pigments, and cholesterol. produced by the liver and stored in the gall bladder, with the gall bladder releasing bile into the duodenum by way of the bile duct in response to cholecystokinin (CCK), which is released by the small intestine in response to the movement of chyme out of the stomach and into the intestines. The pH of bile is between 7.5 and 8.8; like the pancreatic juice, it is alkaline to help neutralize the acidity from the stomach.

Answer 151

serves as substrate to make bile salts, bile salts made from cholesterol not enzymes that do not directly impact chemical digestion mechanical digestion of fats and facilitate chemical digestion of lipids with hydrophobic and hydrophilic regions. as bridge between aqueous and lipid environments allowing fat to be emulsified with the mixture of two immisible liquids of aqueous chyme without bile, fats spontaneously separate out of fixture forming two layers without bile to emsulify dietary fats into micelles which exposes more of surface of the fats to actions of lipase. Bile gets fats into solution and increase surface area by placing them in micelles (mechanical digestion), lipase come in to hydrolyze ester bonds holding lipids together (chemical digestion) systems throughout body use increased surface area to increase efficiency of different processes.

Answer 152

chyme in the duodenum causes the small intestine to release disaccharidases (maltase, lactase, and sucrase), peptidases (including dipeptidases), enterokinase, secretin, and CCK. The first three are enzymes that can digest disaccharides (e.g., lactase breaks down lactose into a galactose and a glucose). Peptidases break down proteins (or peptides, as the name implies). Dipeptidases cleave the peptide bond of dipeptides to release monopeptides (free amino acids). Secretin is a hormone that causes pancreatic juice to be exuded from the pancreas. Finally, CCK, also a hormone, stimulates the release of both pancreatic juice and bile. Bile release is tied to level of fat ingestion, duodenum release hormone enterogastrone to slow movement of chyme

Answer 153

the autonomic nervous system, The parasympathetic division is involved in stimulation (rest and digest) and the sympathetic is involved in inhibition (fight or flight) of digestive activities. The fact that so often we feel sleepy and lethargic (many people call it being in a “ food coma” ) after eating a big meal is due, in part, to parasympathetic activity. Your sympathetic system would decrease blood flow to the digestive organs and decrease their activity.

Answer 154

most fat bypasses the liver. This means it directly enters the circulation without first-pass metabolism. The liver has moderate control over the levels of sugar and protein in the blood because the absorbed carbohydrates and amino acids are first directed to the hepatic portal circulation before being released to the rest of the body

Answer 155

•Simple sugars (e.g., glucose, galactose) and amino acids are absorbed by active transport and facilitated diffusion into the epithelial cells lining the gut. Then, they move across the epithelial cells into the intestinal capillaries. Because blood is constantly passing by the epithelial cells in the capillaries, carrying the carbohydrate and amino acid molecules away from them, a concentration gradient is established such that the capillary blood has a lower concentration of these molecules than the epithelial cells. Thus, the simple carbohydrates and amino acids diffuse from the epithelial cells into the capillaries. The absorbed molecules then go to the liver via the hepatic portal circulation.

Answer 156

• Small fatty acids will follow the same process as carbohydrates and amino acids by diffusing directly into the intestinal capillaries. They are nonpolar, so they can easily traverse the cellular membrane. Larger fats, glycerol, and cholesterol move separately into the intestinal cells but then re-form into triglycerides. The triglycerides and esterified cholesterol molecules are packaged into insoluble chylomicrons, and rather than entering the bloodstream, they enter the lymphatic circulation through lacteals, small vessels that form the beginning of the lymphatic system. These lacteals converge and enter the venous circulation through the lymphatic duct in the neck region (the thoracic duct). Chylomicrons are processed directly in the bloodstream into low-density lipoprotein (LDL), the so-called “ bad” cholesterol. Because this occurs right in the bloodstream, LDL in excess can lead to atherosclerosis. The liver takes up LDL molecules, where they can be repackaged into high-density lipoprotein (HDL, “ good” cholesterol), very low-density lipoprotein (VLDL), or more LDL.

Answer 157

A, D, E, and K

Answer 158

Vitamin B and C, • The water-soluble vitamins are absorbed, along with water, amino acids, and carbohydrates, across the endothelial cells and pass directly into the plasma of the blood.

Answer 159

water absorption overall water balance in body controlled by kidneys. 1.5 meters shorter than small intestine. Divided into cecum (no outlet connects small and large intestines containing appendix), colon (recycling system, sifting through processed food and pulling those last bits of nutrients out of remaining waste products, too little or too much water absorption causing either diarrhea or constipation), and rectum (storage site for feces, consists of indigestible material, water, bacteria, digestive secretions aren’t reabsorbed such as enzymes and bile. . Appendix- tiny structure once thought to be vestigial, warding of certain bacterial infections, inflammation of appendix. Kidneys actually regulate total body water. Anus- opening through which wastes are eliminated and consist of two sphincters: internal (internal sphincter under involuntary control- autonomic from the blastopore, and external anal sphincters (under voluntary control-somatic).

Answer 160

• muscular organ a little larger than your fist, weighing between 7 and 15 ounces. Located between the lungs, it lies behind and a little to the left of the sternum, and it is tilted ever so slightly so that the exterior wall of the right ventricle forms the base of the heart. The walls of the heart are composed of cardiac muscle of varying thickness. Cardiac muscle is found only in the heart, and no other muscle type composes the muscle tissue of the heart. the total volumes of blood passing through the two sides (about 5 liters per minute) are the same. atria are thin-walled muscles that receive blood from the body or lungs, Veins are thin-walled and inelastic vessels that transport blood to the heart (veins converge near the heart) same types of cells comprise both types of vessels and that arteries have much more smooth muscle than veins.

Answer 161

coronary (to heart), carotid, and renal which divide blood flow from aorta into peripheral tissues

Answer 162

Arteries branch into arterioles, and these ultimately lead to capillaries, which perfuse the tissues. On the venous side of a capillary network, the capillaries join together into venules, which join into veins. The deoxygenated blood travels through the veins into the inferior and superior vena cavae (IVC and SVC), the largest veins in the body, which carry the blood to the right atrium. Blood then moves into the right ventricle, which pumps the blood to the lungs via the pulmonary arteries for gas exchange. Finally, blood leaves the lungs through the pulmonary veins and goes to the left atrium.

Answer 163

blood passing through two capillary beds connected by venules before returning to heart. Hepatic portal system- connects the vasculatures of the digestive tract and the liver, and a hypophyseal portal system in the brain connects the vasculatures of the hypothalamus and the pituitary gland/hypophysis

Answer 164

atria and ventricles atrioventricular (AV) valves LAB RAT: (Left Atrium Bicuspid/mitral valve/two leaflets & Right Atrium Tricuspid/three leaflets). (lub) first heart sound, S1, is produced when the two atrioventricular valves close at the start of systole to prevent blood from flowing back into the atria. The second heart sound, S2, dub is produced when the two semilunar valves close at the conclusion of systole to prevent blood from flowing back into the ventricles.

Answer 165

•Contraction: During diastole, the heart is relaxed, semilunar valves are closed, and blood from the atria is filling the ventricles. Contraction of the ventricular muscles generates the higher pressures of systole, whereas their relaxation during diastole causes the pressure to decrease. During systole, ventricular contraction and closure of the AV valves occur, and blood is pumped out of the ventricles. The elasticity of the walls of the large arteries, which stretch out to receive the volume of blood from the heart, allows the vessels to maintain sufficient pressure while the ventricular muscles are relaxed.

Answer 166

Cardiac output-total blood volume pumped by ventricle in a minute product of heart rate (beats/minute) and stroke volume (volume of blood pumped per beat). During periods of rest or exercise, the autonomic nervous system will decrease (parasympathetic) or increase (sympathetic) cardiac output

Answer 167

•autonomic nervous system regulates cardiac output by increasing or decreasing heart rate, with cardiac muscle demonstrating myogenic activity with neural signals modulating rate at which heart beats, continuing to function without input from nervous system. the sinoatrial (SA) node, the atrioventricular (AV) node, the bundle of His (AV bundle) and its branches, and the Purkinje fibers. Impulse initiation occurs at the SA node, which generates 60– 100 signals per minute without any neural input. This small collection of cells is located in the wall of the right atrium. depolarization wave spreads from the SA node, 60-100 signals/minute or beats/minute. two atria to contract simultaneously. Atrial systole (contraction) results in an increase in atrial pressure and more blood pumped into the ventricles. This additional volume of blood forced from the atria into the ventricles is called the atrial kick and accounts for about 5– 30 percent of the cardiac output. Next, the signal reaches the AV node, which sits at the junction of the atria and ventricles. The signal is delayed here to allow for the ventricles to fill completely before they contract. It then travels down the bundle of His and its branches, embedded in the interventricular septum (wall), and to the Purkinje fibers, which distribute the electrical signal through the ventricular muscle, causing ventricular contraction. tachycardia (elevated heart rate). The autonomic division, which consists of parasympathetic (“ rest and digest” ) and sympathetic (“ fight or flight” ) branches, controls the heart. Parasympathetic neurotransmitters slow the heart via the vagus nerve. whereas sympathetic neurotransmitters speed it up.

Answer 168

Only the pulmonary arteries and (fetal) umbilical arteries carry deoxygenated blood. ). Except for the pulmonary and umbilical vein, all veins carry deoxygenated blood.

Answer 169

• Due to their high elasticity, arteries offer high resistance to the flow of blood, which is why the left ventricle must generate the higher pressures. After they are filled with blood, the elastic recoil from their walls maintains a high pressure and forces blood forward. Conversely, veins are capacitive and can carry large amounts of blood owing to their thin, inelastic walls, which stretch out easily and do not recoil. Indeed, three-fourths of our total blood volume may be in venous circulation at any given moment.with the pressure at the bottom of the venous column in the large veins extremely high causing the need for one way valves that allow blood flow when pushed open but shut when pushed back with most veins surrounded my skeletal muscle pushing blood up. Blood pressure is a measure of the force per unit area that is exerted on the wall of the blood vessels. Sphygmomanometers measure the gauge pressure in the systemic circulation, which is the pressure above atmospheric pressure (760 mmHg at sea level). Blood pressure is expressed as a ratio of the systolic (ventricular contraction) to diastolic (ventricular relaxation) pressures. Pressure gradually drops from the arterial to venous circulation, although the largest drop is across the arterioles

Answer 170

varicose veins, which are distended where the blood has pooled with total blood volume increasing during pressure with increasing venous pressure with fetus compressing IVC. blood pools in lower extremities and if blood clots from sluggish movement and carried through pulmonary vasculature it may get stuck

Answer 171

Capillaries are vessels with a single endothelial cell layer, which allows for exchange of nutrients and gases. Capillaries can be quite delicate. broken capillaries allowed erythrocytes to escape into the interstitial space. • By volume, blood is 55% liquid (plasma, aqueous mixture of nutrients, salts, respiratory gases, and hormones_ and 45% cells (erythrocytes, leukocytes, and platelets. All blood cells are formed from the same hematopoietic stem cells, which originate in the bone marrow). In the body, oxygen and nutrients are delivered to the peripheral tissues, and carbon dioxide and other wastes (e.g., hydrogen ions, ammonia) are picked up from the peripheral tissues and delivered to the organs of waste management— the lungs, liver, and kidneys

Answer 172

small population source of blood and immune cell types that are surrounded by stromal cells, which provide them with regulatory singles. when new cells are needed HSC divides to produce one daughter cell remaining in its long-term niche of hematopoietic, and another short-lived daughter cell of multipotent progenitor cell MPP< dividing to produce progenitors committed to generating myeloid (blood) or lymphoid (immune lineagesz0 as more specialized programmed decline in ability to proliferate until cease dividing and terminally differentiated

Answer 173

• specialized cell designed for oxygen transport. RBC transport have no organelles at all. Dissolved in cytoplasm of red blood cells, with each cell also containing 250 million molecules of hemoglobin bind four molecules of oxygen They have a biconcave disk shape that serves a dual purpose. First, this shape assists them in traveling through tiny capillaries. Second, it increases the cell's surface area, which allows for greater gas exchange. Lack nuclei, mitochondria and membranous organelles O2 not used up for cell respiration. Do not divide live for 120 days. cells in the spleen and liver phagocytize them to recycle their parts. There are about 5 million erythrocytes per milliliter of blood. This translates into a total of about 25 billion red blood cells that can carry up to 100 billion oxygen molecules in the total blood volume!

Answer 174

white blood cells, 1% blood volume, 500-1000 per milliliter of blood, defenders against pathogens, foreign cells. •neutrophils, eosinophils, basophils- have cytoplasmic granules in which are compounds toxic to microbes, involved in inflammatory reactions, allergies, pus formation, and destruction of bacteria and parasites.

Answer 175

do not contain granules, and instead consist of lymphocytes which initiate the specific immune response that is a targeted fight against particular pathogens of viruses and bacteria, immediate action or long-term memory) and monocytes (phagocytize foreign matter named macrophage once left the marrow and outside vascular system seek out and ingest agents (brain-microglia)

Answer 176

spleen or lymph nodes- B-cells for antibody generation. Thymus- T-cells- kill virally infected cells and activate other immune cells Antigens are the stimulus for B-cells to make antibodies. After exposure of a B-cell to its specific antigen, the cell transforms into a factory that makes many antibodies .HIV attacked helper T-cells alone are not fatal, the destruction of these lymphocytes prevents the generation of immune responses against opportunistic infections

Answer 177

- cell fragments from broken cells by megakaryocytes- and are present in numbers of 200,000-500,000 per milliliter. platelets protect the vascular system in the event of damage to a vessel by forming a clot, which prevents (or at least minimizes) the pathological loss of blood through vascular damage or injury. connective tissue underlies most of our other tissues and is partly composed of collagen. When platelets come into contact with exposed collagen, they sense this as evidence of injury. In response, they release their contents and begin to aggregate, or clump together. They Release clotting factor thromboplastin converts prothrombin into thrombin with calcium and vitamin K with thrombin. Activates integrin molecules causing them to adhere to circulating proteins of fibrinogen converting fibrinogen into fibrin making fibers that aggregate into woven structure capture red blood cells and platelets forming clots

Answer 178

O cells express neither antigen variant, recipient doesn't recognize as self produce both antibodies. AB no blood antigen is foreign. When an Rh− woman is pregnant with an Rh+ fetus, the risk of erythroblastosis fetal is in subsequent Rh-mismatched pregnancies can usually be avoided by giving the Rh− mother Rh-immune globulin (RhoGAM) during pregnancy and immediately after delivery. Administration of immune globulin will suppress the development of the mother's active immunity, preventing the production of anti-Rh antibodies. Rh+ individuals express the Rh protein on their erythrocytes, and Rh− individuals do not.

Answer 179

•As the first oxygen binds to a heme group on hemoglobin (four subunits) , it induces a conformational shift in the shape of hemoglobin from taut to relax. This shift results in an increase in hemoglobin's affinity for oxygen, making it easier for subsequent molecules of oxygen to bind to the other unoccupied heme groups. Once hemoglobin is full, the removal of one molecule of oxygen also results in a conformational shift. This shift results in a decrease in hemoglobin's affinity for oxygen, making it easier for the other molecules of oxygen to leave the heme groups. •Myoglobin- globular protein responsible for transferring oxygen from hemoglobin to the muscle cells, is composed of only one subunit rapid saturation at low PO2

Answer 180

• A shift to the right means that for a given partial pressure of O2, less O2 will be bound to hemoglobin (more oxygen has been unloaded, and the hemoglobin has a lower percent saturation) due to a decrease in affinity. Several conditions produce a right shift, including an increase in the partial pressure of CO2 which tends to bind to hemoglobin but much less than oxygen , a decrease in pH, and an increase in temperature. These seemingly disparate conditions are associated with periods of increased metabolic rate and signal a need for more oxygen, such as during exercise. For example, we would predict that rapidly and repeatedly contracting muscles would have higher pCO2 (increased metabolism), lower pH (because of increased pCO2 and lactic acid buildup), and higher temperature (increased thermal energy release). Conversely, a shift to the left means that for a given partial pressure of O2, more O2 will be bound to hemoglobin (the hemoglobin has a higher percent saturation) due to an increase in affinity. Fetal hemoglobin, which has a higher affinity for O2 than adult hemoglobin, has a left-shifted curve. vast majority of CO2 exists in the blood in a disguised form, as the bicarbonate ion (HCO3− ) because of presence of carbonic anhydrase catalyzing combination reaction of CO2 and H2O forming H2CO3, carbonic acid, weak acid dissociating into proton and bicarbonate ion soluble in water and readily reformed CO2 in lungs by carbonic anhydrase. With lower pH shifting curve to right- Bohr effect. Hemoglobin reduced affinity for oxygen, dump more oxygen to tissue, downright shame not enough oxygen for race, Metabolic or respiratory disturbances can cause the pH to shift down (acidosis) or up (alkalosis), giving rise to potentially dangerous and life-threatening conditions in which other systems malfunction and proteins become denatured. In response to changing blood pH, the respiratory rate may rise or fall to increase or decrease the amount of carbon dioxide gas excreted, and the kidneys can increase or decrease the amount of bicarbonate ion secreted into the nephron filtrate. For example, in response to a metabolic acidosis (decreased pH), the respiratory rate will increase to reduce the systemic PCO2 so as to shift the reversible system to the left, resulting in a decrease in hydrogen ion concentration (and an increase in the pH)

Answer 181

• Carbohydrates & amino acids, absorbed in small intestine capillaries, enter circulation via hepatic portal system. Fats- absorbed into lacteals in small intestine, bypassing hepatic portal circulation enters systemic circulation via thoracic duct, packaged in lipoproteins, water-soluble. Wastes- CO2, ammonia, urea, enter blood throughout body, down concentrations passing through excretory organs

Answer 182

•Hydrostatic pressure(generated by contraction of heart and elasticity of arteries, measured upstream in large arteries, blood pressure. Force/unit area that blood exerts against walls. /low in capillaries/higher in arteries pushes fluid out of vessels in arterial capillaries (dependent on blood pressure driven by the heart). Oncotic/ Osmotic pressure pulls fluid back into vessels venule end lower then hydrostatic (dependent on the number of particles dissolved in the plasma and plasma proteins). accumulation of excess fluid in the interstitium results in a condition called edema with some fluid taken up by lymphatic system returns to circulatory by thoracic duct

Answer 183

is it the response that cells carry out without learning, and it is a nonspecific barrier between the outside world and the internal organs. for instance in , sweat- there are enzymes that attack bacterial cell walls. Respiratory passage- mucous membranes lined with cilia to trap particulate matter and push up toward oropharynx to be swallowed. Mucous membranes, eyes and oral cavity nonspecific bactericidal enzyme (lysozyme) secreted in tears and saliva. Macrophages called to inflammation by histamine causing vasodilation allow moving out of bloodstream to tissue fever for less bacterial growth. Granulocytes- neutrophils same mechanism. Immune cells/ cells infected by viral particles produce interferon, protein prevents viral replication and dispersion defeat immediately not adaptive

Answer 184

it is when cells learn to recognize and respond to particular antigens, such as the specific immune response including humoral and cell-mediated immunity. humoral immunity circles through humors of body (driven by B-cells and antibodies) and cell-mediated immunity (provided by T-cells- kill virally infected cells). Immunological memory, humoral immunity- B cells , production of antibodies/ immunoglobins week. Bind to specific antigen, can attract leukocytes to phagocytize antigens, or clump together (agglutinate) with antigens to form large insoluble complexes to be phagocytized.

Answer 185

Y shaped- two identical heavy chains and two identical light chains. Disulfide linkages and noncovalent interactions hold the heavy and light chains together. Each antibody has an antigen-binding region at the two top tips of the Y. Within this region, there are specific polypeptide sequences that will bind one, and only one, specific antigenic sequence. Each B-cell makes one antibody, but we have many B-cells, so our immune system can recognize many antigens. The remaining part of the antibody molecule is known as the constant region, which is involved in recruitment and binding of other immune modulators (e.g., macrophages). Epitope- specific part of antigen recognized by immune system

Answer 186

T cells mature in Thymus, while B cells mature in Bone Marrow. It includes T-lymphocytes/memory cells (may form memory cells so that the next exposure to the same antigen will result in a more robust response. T cells bind to antigens presented by major histocompatibility (MHC) class I molecules at a cell's surface) , helper T-cells (coordinate the immune response by secreting chemicals known as lymphokines, interleukins. And are capable of recruiting other immune cells such as ( plasma cells, cytotoxic T-cells, and macrophages as eel as increasing their activity) , suppressor T-cells (helps to tone down the immune response once infection has been adequately contained regulating T cells and B cells to decrease) , and killer (cytotoxic) T-cells (capable of directly killing virally infected cells by secreting toxic chemicals) .

Answer 187

T cell receptor recognize anitgens only on surface of other cells not free floating. Presented on cell in complex of proteins MHC (Major Histocompatibility Complex MHC class I proteins are present on the surface of all cells. MHC class II proteins are only present on immune cells, including macrophages, B cells and T cells. Macrophage phagocytizes pathogen, proteins broken down and displayed on magrophage by MHC class II, helper T cells recognize on macrophage secreting interleukins activating cytotoxic T cells kill infected cells and stimulate B cells to secrete antibodies.

Answer 188

Bruton's agammaglobulinemia with absent B cells, The lack of B-cells results in the absence of circulating antibodies, leading to recurrent bacterial infections. Defenses against viral and fungal disorders are normal because those microorganisms are generally handled by the T-cells. In contrast, DiGeorge's syndrome is a selective T-cell disorder resulting from the underdevelopment or absence of the thymus gland. Circulating antibody

Answer 189

Lymph Nodes (filter lymph and help attack bacteria & viruses). Bone Marrow (immune cell production). Thymus (secretes thymosin— a hormone that stimulates pre-T cells to mature). Spleen (storage area for blood; filters blood & lymph). B cells wait in lymph nodes for particular antigen, B-cell proliferate producing two types of daughter cells. Plasma cells- specialized B cells producing and secreting antibodies large amounts of antibody, memory cells- stay in lymph nodes for use upon being re-exposed to same antigen 7-10 days, primary response. Plasma cells die, memory last lifetime, immune response, secondary response to antigen more rapid. • circulatory system, one-way vessels larger toward center of body toward heart, paralleling venous system carrying lymphatic fluid joining to comprise large thoracic duct in chest delivering fluid to left subclavian vein near heart. Interstitial fluid from capillaries collected by lymphatic vessels and returned to circulation. smallest lymphatic vessels (lacteals) collect fats in the form of chylomicrons from the villi in the small intestine and deliver them into the bloodstream, bypassing the liver. Along the lymphatic vessels are swellings (lymph nodes) that contain immune cells (primarily B-cells). These areas provide a place for antigens from microbes to first interact with the adaptive immune system and allow its activation. Lymph moved by pressure of skeletal muscles with the liquid inside lymph vessels at low pressure with pressure drawn into lymph vessels joins circulatory system at thoracic duct

Answer 190

When the immune system fails to learn the distinction between self and foreign, it may attack self-antigens as if they were foreign, a condition with allergies and autoimmunity considered immune disorders of hypersensitivity reactions

Answer 191

Natural exposure antibodies generated by B-cells once infected. Artificial vaccination production of antibodies, never experience infection. Passively- transfers of antibodies to an individual, antibodies and not B-cells given to individual placenta, mother nursing. Artificial RhoGAM to Rh- mother prevent sensitization to Rh+ fetus

Answer 192

structure- cell body/soma with nucleus, ER, ribosomes present. Dendrites- structures receive information transmitting information to cell body integrated at axon hillock- providing connection between cell body and axon- nerve fiber specialized to carry electrical message, insulated by myelin to prevent signal loss and increasing conduction of signals. Myelin produced by oligodendrocytes in CNS and Schwann cells in PNS. Nodes of Ranvier, exposed area of axon membrane. Nerve terminal/ synaptic bouton enlarged and flattened maximizing neurotransmission to next neuron ensuring proper production of neurotransmitter. Synaptic cleft/ synapse- Neurotransmitter released from the axon terminal traverses the synaptic cleft and binds to receptors on the second neuron. They take in information from many sources (dendrites) and integrate it (axon hillock). Then, they carefully present a coordinated message (action potential traveling down the axon), which results in additional reports (neurotransmitters) distributed to (muscles and glands) Function- neurons use action potentials relaying information to and from C&PN

Answer 193

Resting membrane potential- potential (voltage) difference between the inside of the neuron and the extracellular space. -70mV with inside negative relative to outside. Neuron plasma membrane impermeable to charged species, inside the neuron, [K+] is high and [Na+] is low. Outside of the neuron, [Na+] is high whereas [K+] is low. The negative resting potential is generated by both negatively charged proteins within the cell and the relatively greater permeability of the membrane to K+ compared with Na+. If K+ is more permeable and its concentration is higher inside, it will diffuse down its gradient out of the cell. Na+ wants to go into the cell because it is more negative inside (electrical gradient) and because there is less Na+ inside (chemical gradient). K+ is positively charged, so its movement out of the cell results in a cell interior that is negative. The Na+/K+ ATPase is important for restoring this gradient after action potentials have been fired. They transport three Na+ out of the cell for every two K+ into the cell at the expense of one ATP. Both Na+ and K+ are moved against their gradients by this process; thus, they qualify as active transport. Each time the pump works, it results in the inside of the cell becoming relatively more negative, as two positive charges are moved in for every three that is moved out.

Answer 194

Inhibitory signs makes neurons less likely to fire. an excitatory signal. • As the information is integrated at the axon hillock, depolarization or hyperpolarization may occur. Inhibitory inputs cause hyperpolarization by making the cell more negative. Depolarization is caused by excitatory inputs and makes the cell less negative (relatively more positive). If the axon hillock is depolarized to the threshold value (usually in the range of − 55 to − 40 mV), an action potential will be triggered. Ion channels in the membrane open in response to the depolarization. Since they respond to voltage, they are known as voltage-gated ion channels. There are two types that are responsible for action potentials: Na+ voltage-gated channels and K+ voltage-gated channels. Na+ channels respond strong electric and chemical electrochemical gradient for sodium to move into cell. Cell potential positive from influx, then the channels close when membrane potential reaches +35 mV. Positive potential inside triggers voltage-gated potassium channels to open, with potassium high inside electrochemical drive to move potassium out, restoring negative membrane potential or repolarization, efflux K+ overshoot of resting membrane potential, hyperpolarization. With refractory periods, absolute refractory period, no amount of stimulation cause another potential to occur, relative refractory greater than normal stimulation cause an action potential membrane starting from a potential more negative than resting.

Answer 195

• impulse propagation, sodium from axon hillock rushes in, cause depolarization in regions surrounding it. Depolarization result in opening of sodium channels along axon in wavelike fashion, he depolarization of the membrane to +35 mV causes the sodium channels to slam shut just as the potassium channels begin to open. After the sodium depolarization wave, the potassium channels will cause a repolarization wave that resets the axon for the next action potential. the first set of sodium channels has closed, and the potassium channels have opened, causing repolarization. The action potential is propagated by the ordered opening and closing of these channels. Region of axon refractory immediately after fired so no backward opening or a one-way flow of information. The speed at which action potentials move depends on the length and cross-sectional area of the axon: The longer the axon, the higher the resistance and the slower the conduction. Greater diameters allow for faster propagation as they decrease resistance. Certainly there is a tradeoff for this, and mammalian organisms have developed myelin to cope with it. Myelin is an extraordinarily good insulator, preventing the loss of the electric signal. The insulation is so good that the membrane is only permeable to ion movement at the nodes of Ranvier. Thus, the signal hops from node to node. Transmission that occurs in this manner is referred to as saltatory conduction (from the Latin for “ to jump” )

Answer 196

the synapse is the connection between two neurons, • Most synapses are chemical in nature; they use small molecules referred to as neurotransmitters to send messages from one cell to the next At the nerve terminal, neurotransmitter is stored in membrane-bound vesicles. These vesicles wait for an action potential to come down the axon and depolarize the terminal membrane. They will then fuse with the presynaptic terminal and release the neurotransmitter into the synaptic cleft. This is an example of exocytosis, with neurotransmitters calcium-dependent. Once released into the synapse, the neurotransmitter molecules diffuse across the cleft and bind to receptors on the postsynaptic membrane. This allows the message to be passed from one neuron to the next. neurons may be either inhibitory or excitatory; this distinction truly comes at the level of the neurotransmitter, when binding will result in either hyperpolarization or depolarization of the postsynaptic cell. • Stops to neurotransmitters include- broken down by enzymatic reactions (e.g., the action of acetyl cholinesterase on acetylcholine, using reuptake carriers to be recycled into presynaptic neuron (dopamine, serotonin) or diffuse out of area nitrous oxide. Neurons that carry information from the periphery to the brain or spinal cord are termed afferent neurons, (sensory) whereas the cells that work in the opposite direction are efferent neurons, motor. There are also interneurons that are only involved in local circuits.

Answer 197

• Nervous system bundles many axons into nerves to carry more info: nerves include sensory, motor, or mixed referring to type of info they carry. Mixed nerves carry both sensory and motor information. Much as the axons travel together, neuron cell bodies (somas) will also cluster. In the peripheral nervous system, these collections are known as ganglia. In the central nervous system, they are called nuclei. •

Answer 198

CNS: brain(responsible for integration of sensory information, coordination of motor movement, and cognition)/spinal cord Myelin’s presence differentiates between white matter, consisting of myelinated axons, and gray matter, consisting of unmyelinated cell bodies and dendrites. We can divide the brain into the forebrain, the midbrain, and the hindbrain.

Answer 199

Forebrain- It is further broken down into the telencephalon and diencephalon. It consists of the left and right hemisphere. Each hemisphere can be further sectioned into the frontal, parietal, occipital, and temporal lobes. A large portion of the telencephalon is the cerebral cortex, a region of highly convoluted gray matter that can be seen on the surface of the brain. The cortex is responsible for the highest-level functioning in the nervous system, including creative thought and future planning. It also integrates sensory information and controls movement. Each hemisphere is independent; however, they do communicate through a large connection called the corpus collosum. Nestled below and inside the telencephalon is the diencephalon. It consists of the thalamus and hypothalamus. All ascending sensory information is passed through the thalamus before being relayed to the cortex.

Answer 200

• Midbrain: It passes sensory and visual information to the forebrain, while receiving motor instructions from the forebrain and passing them to the hindbrain.

Answer 201

•Hindbrain: it is made up of the cerebellum, pons, and medulla oblongata, which together are referred to as the brainstem. The cerebellum is a quality control agent. It checks that the motor signal sent from the cortex is in agreement with the sensory information coming from the body. It is what prevents us from falling over when we trip on a sidewalk curb. It rapidly realizes that the motor signal to take a step was not successfully carried out, because we tripped. the cerebellum helps the cortex to adjust to the new situation so that we catch ourselves. The medulla oblongata, often just called the medulla, is the most highly conserved part of the brain. It is responsible for modulating ventilation rate, heart rate, and gastrointestinal tone. With the spinal cord connected to the hindbrain.

Answer 202

• Spinal cord The hindbrain is connected to the other half of the central nervous system, the spinal cord. The spinal cord can be divided into four sections. From the base of the skull to the coccyx, the divisions are cervical, thoracic, lumbar, and sacral. Almost all of the structures below the neck receive sensory and motor innervation from the spinal cord. It is protected by the vertebral column, The spinal cord runs through this column with nerves entering and exiting at each vertebra. In addition to integrating and distributing nerve signals for the brain, the spinal cord can participate in simple reflex arcs of its own. The gray matter is deep to the white matter. As before, the white matter contains axons. In the spinal cord, these are the axons of motor and sensory neurons. The sensory neurons bring information in from the periphery and enter on the dorsal (back) side of the spinal cord. The cell bodies of these sensory neurons are found in the dorsal root ganglia. Motor neurons exit the spinal cord ventrally with the • PNS- The peripheral nervous system has a few more components, including 12 pairs of cranial nerves and 31 pairs of spinal nerves. divide peripheral innervation between the somatic (SNS) and autonomic nervous systems (ANS)

Answer 203

voluntary neuron, interface between the neuron and muscle as the neuromuscular junction. Release of acetylcholine from the nerve terminal onto the muscle leads to contraction. The acetylcholine binding to its receptor on the muscle ultimately leads to muscle depolarization. The SNS is also responsible for providing us with reflexes, which are automatic. They do not require input or integration from the brain to function. There are two types of reflex arcs: monosynaptic and polysynaptic. Reflexes usually serve a protective purpose

Answer 204

Monosynaptic- there is a single synapse between the sensory neuron that received the information and the motor neuron that responds. A classic example is the knee-jerk reflex. When the patellar tendon is stretched, information travels up the sensory neuron to the spinal cord, where it interfaces with the motor neuron that contracts the quadriceps muscle. The net result is a straightening of the leg, which lessens the tension on the patellar tendon. We should notice that the reflex is responding to a potentially dangerous situation. If the patellar tendon is stretched too far, it may tear, damaging the knee joint

Answer 205

polysynaptic- In a polysynaptic reflex arc, there is at least one interneuron between the sensory and motor neuron. A real-life example is your reaction to stepping on a tack, which involves the withdrawal reflex. The foot that steps on the tack will be stimulated to jerk up; this is a monosynaptic reflex. However, if we are to maintain our balance, we need our other foot to go down and plant itself on the ground. For this to occur, the motor neuron that controls the opposite (downward-moving) leg must be stimulated. Interneurons in the spinal cord provide the connection from the incoming sensory information for the leg being jerked up to the motor neuron for the supporting leg.

Answer 206

• Autonomic nervous system- The ANS is sometimes referred to as the involuntary nervous system, as it requires no conscious control. cardiac and smooth muscle are both innervated by the autonomic nervous system. Smooth muscle is found throughout the body, including the blood vessels, the bronchi, the bladder, and the gastrointestinal tract. autonomic nervous system exerts great control over blood pressure, ventilation dynamics, urination, and digestion. The primary difference between the SNS and ANS is that the ANS is a two-neuron system. A motor neuron in the SNS goes directly to the muscle without synapsing. In the ANS, the neurons play a game of telephone; two neurons work in series to transmit messages. The first neuron is known as the preganglionic neuron, whereas the second is the postganglionic neuron. The preganglionic neuron's soma is in the CNS, whereas its axon travels to a ganglion in the PNS. Here, it synapses on the cell body of the postganglionic neuron, which then affects the target tissue (it can be muscular or glandular). Although the ANS can regulate each organ individually, it can also have coordinated effects. These can be divided into sympathetic and parasympathetic effects.

Answer 207

Sympathetic- ANS that is responsible for “ fight-or-flight.” increase blood flow to the heart and skeletal muscle, while decreasing it to the GI tract and kidneys. In addition, increasing breathing rate and heart rate would ensure an adequate supply of oxygen to meet the demands of the rapidly contracting skeletal muscles. Finally, our pupils would dilate. Preganglionic neurons use acetylcholine, whereas postganglionic neurons in the sympathetic nervous system use norepinephrine. Preganglionic sympathetic neurons can also cause the release of epinephrine from the adrenal medulla.

Answer 208

Parasympathetic nervous system- increased blood flow to the organs of digestion and excretion with a concomitant decrease in flow to the skeletal muscle and heart. heart rate and ventilation rate would decrease. The vagus nerve, which is one of the 12 cranial nerves, is responsible for many of the parasympathetic effects in the thoracic and abdominal cavities. The parasympathetic nervous system uses acetylcholine as a neurotransmitter at both preganglionic and postganglionic neurons.

Answer 209

* Sensory information enters the spinal cord on the dorsal side, whereas motor signals leave from the ventral surface * Senses- interoceptors, proprioceptors, and exteroceptors. Interoceptors monitor internal environment parameters, such as blood volume, blood pH, and partial pressure of CO2 in the blood. Proprioceptors are important for our position sense. Exteroceptors are responsible for monitoring the external environment, such as light, sound, touch, taste, pain, and temperature. Furthermore, nociceptors sense pain and relay that information to the brain

Answer 210

* Eye- specialized organ used to detect light (in the form of photons). Most of the exposed portion of the eye is covered by a thick layer known as the sclera, white of eye. The eye is supplied with nutrients and oxygen by the choroid, which is directly beneath the sclera. The innermost layer of the eye is the retina, which contains the actual cells (photoreceptors) that transduce the light into electrical information the brain can process. * Light first passes through the cornea, a transparent structure that bends and focuses it. Light rays then move through the pupil. The muscular, pigmented iris can adjust the amount of light entering the eye by altering the diameter of the pupil; the more light available, the greater the degree of constriction. After the pupil, the light is passed through the lens, which does the final focusing. Ciliary muscles can adjust the thickness of the lens, which focuses the image on the retina. light has been focused by these three structures, it will impinge on the photoreceptors of the retina and be turned into an electrical signal. * rods and cones. Rods are responsible for transmission of black-and-white images and respond to low-intensity illumination. This makes them useful for night vision. Cones come in three varieties and manage color images. Each type of cone contains a pigment that absorbs a different wavelength of light; these wavelengths correspond to the colors red, green, and blue. Rods have only one pigment, rhodopsin, which explains their ability to respond only to black and white. the photoreceptors send a signal to the bipolar cells, which relay the information to the retinal ganglion cells. The axons of the ganglion cells bundle to form the optic nerve, which then exits the back of the eye. Because the optic nerve takes up space on the back of the eye, displacing photoreceptors, there is a blind spot at the site of exodus. Since we have two eyes, this is rarely a problem, as each eye compensates for the blind spot of the other. Color blindness is a result of lacking one, two, or three of these sets of cones. Total color blindness is most commonly due to a complete lack of cones. * The eye is filled with fluid to simplify the transmission of light to the retina. Aqueous humor is secreted near the iris at the base of the eye. It then travels to the anterior chamber, where it exits and eventually enters the venous blood.

Answer 211

• Ear- The ear transduces sound waves (mechanical disturbances of pressure) into electrical signals that can be interpreted by the brain. In addition, it houses certain nerves that help coordinate balance. The outer ear, which consists of the auricle and auditory canal, collects the waves and channels them to the tympanic membrane. The tympanic membrane is the beginning of the middle ear, which also includes the ossicles (malleus, incus, and stapes). The tympanic membrane vibrates due to sound waves pushing on it, and the ossicles move back and forth. These three bones then transmit the information through the oval window to the fluid-filled inner ear, which is made up of the cochlea and semicircular canals. The movement of the ossicles on the oval window creates fluid waves in the inner ear that depolarize the hair cells of the cochlea. This is the transduction mechanism that generates an electrical signal the nervous system can interpret. The action potentials from the hair cells travel along the auditory nerve (vestibulocochlear nerve) to the brain. The semicircular canals are important for balance. There are three per ear, one oriented in each plane (think x-, y-, and z-axes). The canals are filled with a fluid called endolymph, whose movement through the canals puts pressure on the hair cells inside. Because there is a canal in each dimension, the brain can integrate the signal from each canal and maintain balance, as well as interpret sudden acceleration and deceleration.

Answer 212

* Chemical senses- olfaction and gustatation for smell and taste. Taste receptors, or taste buds, are located on the tongue, soft palate, and epiglottis. Taste buds are composed of approximately 40 epithelial cells. The outer surface of a taste bud contains a taste pore, from which microvilli, or taste hairs, protrude. The receptor surfaces for taste are on the taste hairs. Interwoven around the taste buds is a network of nerve fibers that they stimulate. These neurons transmit gustatory information to the brainstem via three cranial nerves. There are four kinds of taste sensations: sour, salty, sweet, and bite * Smell- Olfactory receptors are found in the olfactory membrane, which lies in the upper part of the nostrils over a total area of about 5 cm2. The receptors are specialized neurons from which olfactory hairs, or cilia, project. These cilia form a dense mat in the upper nasal mucosa. When odorous substances enter the nasal cavity, they bind to receptors in the cilia, depolarizing the olfactory receptors. Axons from the olfactory receptors join to form the olfactory nerves. The olfactory nerves project directly to the olfactory bulbs in the base of the brain.

Answer 213

passes through the nasal cavity, where it is filtered through mucous membranes and nasal hairs entrapping free-floating particulate matters. numerous cilia in the nasal pathway trap particulate matter (such as dust) so that we don't breathe it into our lungs and cough or sneeze it up clearing lower respitatory . mouth and nose serve several important purposes in breathing. They allow for dirt and particulate matter to be removed from the air in addition to warming and humidifying the air before it reaches the lung, and they detecting odors. air passes into the pharynx and the larynx. The pharynx serves as a tunnel between the mouth and esophagus through which food travels. whereas the larynx is only a pathway for air. To keep food out of the respiratory tract, the opening of the larynx (glottis) is covered by the epiglottis during swallowing. From the larynx, air passes into the cartilaginous trachea and then into the mainstem bronchi (one per side). These bronchi continue to divide into smaller structures known as bronchioles, which divide further until they end in tiny structures in which gas exchange occurs (the alveoli). The bronchi and trachea also contain ciliated epithelial cells to catch material that may have made it past the initial check in the nose. Each alveolus is coated with surfactant, a detergent that lowers surface tension and prevents the alveolus from collapsing on it. A network of capillaries surrounds each alveolus to carry oxygen and carbon dioxide. The branching and minute size of the alveoli allow for an exceptionally large surface area for gas exchange

Answer 214

lungs in thoracic cavity, separated from organs of digestion by diaphragm necessary for inspiration, breathing controlled autonomicall and composed of skeletal muscle, under somatic control. chest wall forms one side of the thoracic cavity. Membranes known as pleurae (singular: pleura) surround each lung. The pleurae are a closed sac against which the lung grows. The surface adjacent to the lung is visceral, and all other parts of the sac are parietal. The space within the sac is referred to as the intrapleural space, which in our bodies contains a thin layer of fluid. This fluid helps lubricate the two pleural surfaces. In addition, there is a pressure differential between the intrapleural space and the lungs

Answer 215

- diaphragm as well as the external intercostal muscles (one of the layers of muscles between the ribs) contract to expand the thoracic cavity. As the cavity enlarges, the diaphragm flattens down, and the chest wall moves out. Intrapleural volume increases. increase in intrapleural volume leads to a decrease in intrapleural pressure. The gas in the lungs is at atmospheric pressure, which is now higher than the pressure in the intrapleural space. The lungs will expand into the intrapleural space and air will be sucked in from a higher-pressure environment. This mechanism is referred to as negative-pressure breathing, because the driving force is the lower (relatively negative) pressure in the intrapleural space compared with the lungs (alveoli).

Answer 216

As the diaphragm and external intercostal relax move upward chest cavity decreases, the chest cavity decreases in size (volume). pressure in the intrapleural space is higher than in the lungs, which is still at atmospheric level. So air will be pushed out, resulting in exhalation. speed this process up by using the internal intercostal muscles, which oppose the externals and pull the rib cage down, actively decreasing the volume of the thoracic cavity. surfactant prevents the complete collapse of our alveoli during exhalation by reducing surface tension at the alveolar surface. Expiration during calm states is entirely due to elastic recoil of the lungs and musculature. bronchus, bronchiole, alveolar ducts, and alveolar sacs to finally reach one of many alveoli.

Answer 217

• Muscle contraction is required to create the negative pressure in the thoracic cavity that forces air in during inspiration volume increase during inhalation reducing intrapleural pressure causing lungs to expand and fill with air. Positive pressure breathing occurs when patients are on ventilators when air is forced into lungs because the pressure is greater in ventilator than lungs.

Answer 218

Our ventilation is primarily regulated by neurons (ventilation centers) in the medulla oblongata that rhythmically fire to cause regular contraction of respiratory muscles. These neurons are primarily sensitive to carbon dioxide concentration. As the partial pressure of carbon dioxide rises, the respiratory rate will increase to counter it. Chemoreceptors on the neurons' surfaces monitor changes in the blood's pH. control our breathing through the cerebrum. We can choose to breathe more rapidly or slowly; however, extended periods of hypoventilation would lead to increased carbon dioxide levels and an override by the medulla oblongata (which would jump-start breathing). The opposite process (hyperventilation) would blow off too much carbon dioxide and inhibit ventilation.

Answer 219

* Spirometer- measures the amount of air normally present in lungs and rate at which ventilation occurs usually 12 breaths per minute. * TLC = RV + VC and that VC = TV + ERV + IRV. * Total lung capacity (TLC) in healthy human beings is about six to seven liters. If we breathe in as much as possible, the total amount of air in our lungs at this point is the TLC. * breathe out until we cannot breathe out any more (i.e., we force out all air using our musculature) total amount we forced out was the vital capacity (VC) amount can actually vitally use. * Residual volume- amount left over is the residual volume(RV). There will always be some air left over, because expelling it all would require lung collapse, certain volume of air can never be removed from healthy lungs during normal breathing. Lung collapse occurs when an injury to chest where parietal pleura is ruptured and resulting in air entering intrapleural space collapsing lung, alveoli coated with layer of surfactant reducing high surface tension of fluid lining in alveoli and prevents lung from collapsing in exhalation * Tidal volume- difference in level between high breathing in and low breathing out. Shallow breath only what needed. Tidal volume not VC, forced out, air that naturally comes out with exhalation. If we use respiratory muscles to push air out, the last bit of air that exits is the expiratory reserve volume (ERV). Because there is an expiratory reserve volume, there must also be an inspiratory reserve volume (IRV), which is the amount of extra air we can take in after a tidal breath.

Answer 220

capillaries bring deoxygenated blood from pulmonary arteries, stemming from right ventricle, single-celled alveolar layer allow for diffusion of CO2 from blood into lungs and oxygen in opposite direction. Oxygenated blood returns to heart via pulmonary veins. The driving force is the pressure differential of the gases. Since blood is deoxygenated as it enters, it has a relatively low partial pressure of oxygen and a relatively high pressure of carbon dioxide, facilitating the transfer of each down its respective concentration gradient. Since the gradient between the blood and air in the lungs is already present as the blood enters the lungs, no energy is required for gas transfer. • partial pressure of O2 in the greater alveoli flows down its partial pressure gradient from the alveoli into the pulmonary capillaries, where it can bind to hemoglobin for transport. Meanwhile, partial pressure of CO2 higher in blood and flows down its partial pressure gradient from the capillaries into the alveoli for expiration. gas diffuses across respiratory membrane/pulmonary membrane to travel between alveoli and capillaries.

Answer 221

* Thermoregulation- lowering of the blood temperature is accomplished through panting, a state in which the animal breathes far more rapidly than usual. This increased respiratory rate maximizes the area of the upper respiratory surfaces that come in contact with air from the outside environment, promoting cooling of the blood through water evaporation from mucosal surfaces of the respiratory tract and saliva in the mouth. Since energy (in the form of heat) is required for water to evaporate, evaporation facilitates cooling. * Higher altitude: we can breathe more rapidly to try and increase gas exchange; second, we could make more red cells to carry the oxygen (polycythemia). we could develop more blood vessels (vascularization), which would facilitate the distribution of a higher amount of oxygen to tissues. Alter binding dynamics of hemoglobin to oxygen

Answer 222

it is located behind the digestive organs • Cortex- outermost layer, medulla- beneath cortex. Renal hilum- deep slit in center of medial surface, widest part of ureter, renal pelvis spans entire width of renal hilum, The renal artery, renal vein, and ureter enter and exit the kidneys through the renal hilum. The afferent arterioles lead into capillaries, and the efferent arterioles branch out from them. A comes before E in the alphabet, with C in between, just as the Afferent arterioles come before the Efferent ones, with the Capillaries in between. increase salt and water reabsorption. The kidney also produces erythropoietin, which stimulates bone marrow to increase production of erythrocytes. It is secreted in response to low oxygen levels in the blood. Patients with chronic kidney disease can become anemic as a result of impaired erythropoietin production, causing inadequate red cell production from the bone marrow.

Answer 223

two sets of capillaries in series through blood travel returning to heart. The renal artery branches out and travels through the medulla and into the cortex as afferent arterioles. The capillaries that are derived from these afferent arterioles are known as glomeruli (singular: glomerulus) and together form a highly convoluted structure. After blood passes through the glomerulus, the efferent arterioles lead blood away from it. As is the case in portal systems, the glomerular capillaries lead to a second set of arterioles (the efferent) rather than venules. Like most arterioles, the efferent arterioles also lead to a set of capillaries. This second set of capillaries is known as the vasa recta. afferent arterioles carry blood toward the glomeruli; efferent arterioles carry blood away from the glomerulus.

Answer 224

net of capillaries surrounded by cup-like Bowman's capsule leads to a long tubule with many distinct areas proximal convoluted tubule, descending and ascending limbs of the loop of Henley, the distal convoluted tubule, and the collecting duct.

Answer 225

• The nephron's first step is filtration. In the kidneys, approximately 20 percent of the blood that passes through the glomerulus is filtered into Bowman's space. The collected fluid is known as the filtrate. It is similar in composition to blood but does not contain cells or proteins due to the filter's ability to select based on size. In other words, molecules or cells that are larger than glomerular pores will remain in the blood. On to the efferent arterioles and then through a second capillary network, the vasa recta. The filtrate is isotonic o blood so that neither the capsule nor the capillaries swell. Our kidneys filter about 180 liters a day, which is approximately 36 times our blood volume. Small molecules dissolved in the fluid will pass through the tiny pores (e.g., glucose, which is later reabsorbed), whereas large molecules such as proteins and blood cells will not. If blood cells or protein are found in the urine, this indicates a health problem at the level of the glomerulus.

Answer 226

• Secretion- secretes salts, acids, bases and urea into tubule by active and passive transport. Similarly, our kidneys can get rid of ions or other substances when they are present in relative excess in the blood. Secretion is also a mechanism for excreting wastes that are simply too large to pass through glomerular pores. Cortex- lowest solute concentration proximal and distal

Answer 227

• Reabsorption- Some compounds that are filtered and/or secreted may be taken back up for use. Certain substances are always reabsorbed, like glucose and amino acids.

Answer 228

selective permeability and osmolarity gradients allowing to reabsorb water, salt, and nutrients from filtrate and selectively excreting waste. molecules must be able to cross the cell membrane to enter a cell, compounds that we want to reabsorb and keep must be able to leave the filtrate (by crossing the plasma membranes of the cells lining the tubule. The proximal and distal tubules are capable of reabsorbing most substances (including water). The ascending and descending limbs of the loop of Henley and the collecting duct are a bit more selective. The descending limb is permeable to water but not salt, whereas the ascending limb is permeable to salt but not water. The collecting duct almost always reabsorbs water, but the amount is variable. When the body is very well hydrated, the collecting duct will be fairly impermeable to salt and water conserving water antidiuretic hormone and aldosterone will each act to increase the permeability of the collecting duct, allowing for greater water reabsorption and more concentrated urine output inserting aquaporin’s.

Answer 229

The kidney is capable of altering the osmolarity of the interstitium (the tissue surrounding the tubule). This creates a gradient that, coupled with the selective permeability mentioned above, will allow us to reabsorb and excrete compounds as needed. Together, they work as a countercurrent multiplier system. In the normal physiological state, the osmolarity in the cortex is approximately the same as that in the blood and remains at that level. As we descend deeper into the medulla, the osmolarity in the interstitium can range from isotonic with blood (when trying to excrete water) to four times as concentrated (when trying to conserve water). Water will move out of the tubule, into the interstitium, and eventually back into the blood if the concentration of solute is very high in the surrounding tissue, thereby conserving the water. If the concentration is the same in the tubule and in the interstitium, there is no driving force (gradient), and the water will be lost in urine. Creates urine hypertonic to blood.

Answer 230

the proximal convoluted tubule, glucose, amino acids, soluble vitamins, and the majority of salts are reabsorbed along with water. Almost 70 percent of filtered sodium will be reabsorbed here, but the filtrate remains isotonic to the interstitium. The descending limb of the loop of Henle is only permeable to water. As we travel down it, the concentration of the surrounding tissue will increase (we could also say it's hypertonic), which will drive water out of the tubule. Water loss increases the filtrate's osmolarity to roughly the same level as the interstitium's. The ascending limb is permeable only to salt. As the filtrate moves back up the loop toward the cortex, the concentration in the area surrounding the tubule drops and salt will be actively pumped out. Again, the filtrate becomes isotonic to the interstitium. The distal convoluted tubule maintains the same concentration as the cortex by reabsorbing salt and water in roughly equal proportions. The final concentration of urine will depend on the permeability of the collecting duct. As permeability increases, so does water removal, which concentrates the urine

Answer 231

* Aldosterone directly increases sodium reabsorption, and water follows. Aldosterone is a steroid hormone that is secreted by the adrenal cortex in response to decreased blood volume, less fluid leading to lower blood pressure (hypotension). Aldosterone is released from the adrenal glands in response to an increase in angiotensin, which itself is positively regulated by renin. If we reabsorb more sodium, water will flow with it. This has the net effect of increasing blood volume and therefore blood pressure. Aldosterone will also increase potassium excretion * ADH makes the collecting duct more leaky (permeable) to water such that it will re-enter the interstitium. Antidiuretic hormone (also known as vasopressin) is a peptide hormone that directly alters the permeability of the collecting duct. It allows more water to be reabsorbed by making the cell junctions of the duct leaky. Increased concentration in the interstitium (i.e., hypertonic to the filtrate) will then cause the reuptake of water from the tubule. ADH is made in the hypothalamus, stored in the posterior pituitary, and secreted when blood osmolarity is high. ADH and aldosterone increase water reabsorption.

Answer 232

• Excretion- collecting duct is excreted, collecting in renal pelvis, fluid carrying urea, uric acid, and excess ions (sodium, potassium, magnesium, and calcium) flows through ureter to bladder, stored until excreted in urethra. No urine should contain blood, protein, or glucose, blood indicates problem of glomerulus; glucose, amino acids, and small proteins should be fully reabsorbed

Answer 233

hepato. produces bile, aiding in absorption of fats by solubilizing them. Assisting with blood glucose regulation and elimination of nitrogen waste through urea. Nutrient absorbed during digestion delivered to liver through hepaticportal vein. After meal liver will combine circulating glucose molecules into glycogen, a polymerized storage form. Famine- this glycogen can be broken back down into glucose and released into the bloodstream. Additionally, the liver can make new glucose from a variety of precursors through gluconeogenesis. Storage for glucose, deals with nitrogenous waste products shortages of glucose, amino acids used for vital processes undergoing deamination, removal of amino group resulting in toxic ammonia so combine with CO2 creating urea. Detoxification other functions •Storage of vitamins and cofactors (iron and B12) •Destruction of old erythrocytes •Synthesis of bile •Synthesis of various blood proteins •Defense against antigens •Beta-oxidation of fatty acids to ketones •Interconversion of carbohydrates, fats, and amino acids. • Large intestine- capable of reabsorbing salt and water (but not directing overall fluid balance). This organ can also excrete certain salts, such as calcium and iron.

Answer 234

* largest organ, 16% total body weight, protecting us from elements and disease, these layers are the epidermis, dermis, and hypodermis (subcutaneous layer) deriving from ectodermal layers. * Epidermis- stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, and stratum basalis. The deepest layer is responsible for further proliferation. The outer layers are formed from cells that have pushed up from the stratum basalis. As these cells reach the outermost layer, they die and lose their nuclei, forming the scales (squames) of keratin with the tight packing serving an immune function and helps prevent loss of fluids and salt, with hair projecting above skin with opening for sweat glands. * Dermis- The upper layer (right below the epidermis) is the papillary layer, which consists of loose connective tissue. Below the papillary layer is the denser reticular layer. With sweat glands, sense organs for touch and temperature, blood vessels and hair follicles in dermis * Hypodermis- layer of connective tissue that connects our skin to our bodies

Answer 235

protects us from elements and microbes, UV protection, thermoregulation in endotherms, and transduction of sensory information from outside. Melanocytes- epidermal cells secrete melanin-protecting DNA from UV light. Receptor for touch and temperature, achieved vasodilation, vasoconstriction, and sweating using heat of bodies as heat of vaporization energy barrier. Heat loss prevented Pads of subcutaneous fat provide insulation. Hair also contributes by trapping heat close to the skin's surface. Shivering in the cold is a result of involuntary muscle contraction and relaxation, a by-product of which is heat. Fat serves as storage for excess energy, generating 100 ATP per molecule of triacylglycerol

Answer 236

* animals - Evaporation of warmth results in a cooling effect, but they evaporate warm air from the respiratory passages rather than warm water from skin. quite thick and is called fur. Their fur serves the same function as the hair we already discussed but does so much more effectively. Animals that maintain a constant temperature are known as endotherms or homeotherms, whereas those whose temperature depends on the external environment (e.g., snakes) are called ectotherms/cold-blooded/poikilotherms. enter a state of decreased arousal (torpor) during periods of excessive heat or cold. During the warm months, some desert animals may choose to estivate. during the winter months, the analogous process is called hibernation. In both cases, metabolic rate, heart rate, and respiration are far below normal. The benefit of these modes is the minimal expenditure of energy in an inhospitable environment. * Homeostasis- The ability to maintain a constant internal environment despite a changing external environment

Answer 237

autocrine, paracrine, and endocrine. • In autocrine signaling, the same cell is stimulated. This cytokine can then bind to the same T-cells to increase their immune functionality. Paracrine signaling occurs between cells that are placed close to one another; we can use two neurons signaling between the hypothalamus and pituitary Endocrine- at a distance- follicle-stimulating hormone (FSH), which is released by the anterior pituitary but exerts its effects at the level of the gonads

Answer 238

hypothalamus, the pituitary, the testes and ovaries, the pineal gland, the kidneys, the gastrointestinal glands, the heart, and the thymus. Cells capable pancreatic islets of Langerhans, which are primarily responsible for glucose homeostasis. Hormones come in two varieties: peptide and steroid

Answer 239

* hypothalamus- forebrain above pituitary and below thalamus with hypothalamus controlling pituitary by hormones directly connected to both using paracrine signaling. Receives input from neural sources, can be regulated by negative feedback, and controls both anterior and posterior pituitary just differently. Functions as thermostat regulating body temperature, from nerves and adjusting thyroid and adrenal if necessary. * the hypothalamus secretes compounds into the hypophysealportal system hormones are released from the hypothalamus into this portal bloodstream. They then travel down the pituitary stalk and bind to receptors in the anterior pituitary, where they stimulate the release of other hormones. concentrations of the final effector molecule rise (e.g., cortisol), negative feedback to the hypothalamus and pituitary decreases their release of the upstream signaling molecules (e.g., CRF and ACTH, respectively).

Answer 240

first is the hypothalamic hormone, whose binding in the anterior pituitary affects the release of the second hormone or set of hormones: Increased release from the hypothalamus will cause increased release of the corresponding hormone from the anterior pituitary. Prolactin is constitutively released from the anterior pituitary and is inhibited by prolactin inhibitory factor. Gonadotropin-releasing hormone (GnRH)→ follicle-stimulating hormone (FSH) and luteinizing hormone (LH) • Growth hormone-releasing hormone (GHRH)→ growth hormone (GH) • Prolactin inhibitory factor (PIF) → prolactin • Thyroid-releasing hormone (TRH) → thyroid-stimulating hormone (TSH) Corticotropin-releasing factor (CRF) → adrenocorticotropic hormone (ACTH) seven products of the anterior pituitary, think FLAT PEG: FSH, LH, ACTH, TSH, Prolactin, Endorphins, and GH • Release of CRF (also known as CRH, cortisol-releasing hormone) from the hypothalamus will stimulate the anterior pituitary to generate ACTH. ACTH will then cause the adrenals to increase the level of cortisol being secreted into the blood. cortisol can inhibit the hypothalamus and anterior pituitary from releasing CRF and ACTH, respectively. • Hypothalamus and posterior pituitary- neurons in the hypothalamus send their axons, own the pituitary stalk and into the posterior pituitary, which can release oxytocin and anti-diuretic hormone (ADH). ADH

Answer 241

Direct hormones will bind to receptors on their target organs and have a direct effect (i.e., no intermediate is needed). Tropic hormones also bind to receptors on organs, but rather than resulting in immediate changes, they cause the release of effector hormones (i.e., they act as an intermediate). FLAT PEG, direct (PEG) versus tropic (FLAT) effects.

Answer 242

Growth hormone is named for what it does: It promotes the growth of bone and muscle. Growth hormone prevents glucose uptake in certain tissues (no growing ones) and stimulates the breakdown of fatty acids increasing glucose. growth occurs at the epiphyseal plates of the long bones; these plates seal during puberty. An excess of GH released in childhood (before this closure) can cause gigantism. A deficit results in dwarfism. In adults, the situation is slightly different. Because the long bones are sealed, GH still has an effect, but it is in the smaller bones. Bone remodeling occurs throughout life, and an excess of GH in adulthood will affect smaller bones disproportionately. The medical condition is known as acromegaly. The bones most commonly affected are those in the hands, feet, and head. prolactin and the endorphins. Prolactin is more important in females than in males, where it stimulates milk production in the mammary glands. Endorphins have a direct effect on pain modulation by decreasing the perception of pain.

Answer 243

causing the release of another hormone at the organ level. ACTH is regulated by CRF. It induces the adrenal cortex to release glucocorticoids affecting sugar. TSH is released in response to TRH stimulation. TSH is appropriately named, as it stimulates the thyroid to take up iodine and release thyroid hormone. Both LH and FSH are secreted when GnRH levels rise. They affect the ovaries and testes.

Answer 244

The posterior pituitary contains the nerve terminals of neurons whose bodies are in the hypothalamus. The posterior pituitary receives and stores two hormones produced by the hypothalamus, ADH and oxytocin. These hormones are released into the bloodstream by the posterior pituitary. Oxytocin is secreted during childbirth and allows for coordinated contraction of uterine smooth muscle. Its secretion may also be stimulated by suckling, which in turn will lead to increased milk production. ADH is secreted in response to increased blood osmolarity (sensed by osmoreceptors) or low blood volume (sensed by baroreceptors). Its action is at the level of the collecting duct, where it increases the permeability of the duct to water. The net effect is a greater reabsorption of water from the nephron filtrate, resulting in greater retention of water and expansion (and dilution) of the vascular compartment.

Answer 245

The thyroid is controlled by the pituitary (TSH) and the hypothalamus (TRH). The human thyroid is on the front surface of the trachea; setting basal metabolic rate and calcium homeostasis. It mediates the first effect by releasing thyroxin and triiodothyronine (the thyroid hormones), whereas calcium levels are controlled by calcitonin.

Answer 246

* Thyroxine (T4) and triiodothyronine (T3) are both produced by the iodination of the amino acid tyrosine in the follicular cells of the thyroid. The numbers 3 and 4 refer to the number of iodine atoms attached. Thyroid hormones are capable of resetting the basal metabolic rate of the body by making energy production more or less efficient, as well as altering the utilization of glucose and fatty acids. Increased amounts of T3 and T4 will lead to increased cellular respiration. They will also cause a greater amount of protein and fatty acid turnover by speeding up both synthesis and degradation of these compounds. High plasma levels of thyroid hormones will lead to decreased TSH and TRH synthesis * deficiency of iodine- hypothyroidism, in which thyroid hormones are secreted in insufficient amounts or not at all. The condition is characterized by lethargy, decreased body temperature, slowed respiratory and heart rate, cold intolerance, and weight gain. Children result in mental retardation and developmental delay (cretinism * excess- tumor or thyroid overstimulation, may lead to hyperthyroidism. heightened activity level, increased body temperature, increased respiratory and heart rate, heat intolerance, and weight loss.

Answer 247

Parathyroid- parathyroid hormone (PTH). The parathyroid is four small pea-shaped structures that sit on the posterior surface of the thyroid. PTH serves as an antagonistic hormone to calcitonin. It functions to increase plasma levels of calcium by reversing the effects of calcitonin; namely, it decreases excretion of calcium through the kidneys, increases absorption of calcium in the gut, and increases bone resorption, thereby freeing up calcium. PTH also activates vitamin D to its active form, which is required for the absorption of calcium in the gutAs levels of plasma calcium rise, PTH secretion is decreased. important functions of calcium: Principal component of bone, Regulator of muscle contraction, Cofactor for normal blood clotting. In addition, calcium also plays a role in cell movement, exocytosis, and neurotransmitter release.

Answer 248

Adrenal- located on top of the kidneys, one on each side- consist of a cortex and a medulla. The distinction is more than anatomical; each part of the gland is responsible for secretion of a different hormone • cortex- The adrenal cortex secretes a set of hormones called the corticosteroids. These compounds are secreted in response to ACTH stimulation from the anterior pituitary, which itself responds to CRF from the hypothalamus. All of the corticosteroids are steroid hormones (derived from cholesterol); they may be divided into three functional classes: glucocorticoids, mineralocorticoids, and cortical sex hormones. One way to remember the corticosteroids is to think of the three s's of the adrenal cortex: sugar, salt, and sex • glucocorticoids- cortisol& cortisone- increase gluconeogenesis and decrease protein synthesis. Cortisol and cortisone can also decrease inflammation and immunological response Cortisol is often known as the stress hormone, as it is released in response to physical or emotional stress. • Mineralocorticoids- healthy mineral balance. control salt balance in coordination with the kidneys. Aldosterone causes increased reabsorption of sodium and thereby water. The increased sodium and water leads to expansion of the blood volume and a higher blood pressure. Aldosterone can also affect the levels of potassium and hydrogen ions. It enhances the secretion of these two atoms into the tubule. Potassium and hydrogen will be excreted from the body in the urine.

Answer 249

• The secretion of aldosterone is under the control of the renin-angiotensin-aldosterone system. Once fluid volume is restored, there is a decreased drive to stimulate renin release, thus serving as the negative feedback mechanism for this system. n addition to stimulating the secretion of aldosterone, which increases blood volume and hence blood pressure, angiotensin II also increases blood pressure directly by a powerful vasoconstrictive effect. Angiotensin converting enzyme (ACE) inhibitors block the conversion of angiotensin I to angiotensin II, inhibiting vasoconstriction and actually producing vasodilation. Therefore, ACE inhibitors frequently are prescribed for the treatment of high blood pressure and congestive heart failure. (In the latter case, vasodilation helps reduce the resistance against which the failing heart must pump.)

Answer 250

• Cortical sex hormones- The adrenals are also capable of making male sex hormones (androgens). Because normal males make much larger amounts of androgens in the testes, the hormones secreted from the adrenals are relatively unimportant. In females, however, the lower baseline of androgens is subject to greater perturbation. An increase in adrenal sex hormones may have masculinizing effects, such as excess hair growth and an increase in other male secondary sex characteristics.

Answer 251

• Adrenal medula- Nestled inside the adrenal cortex is the adrenal medulla. A derivative of the nervous system, it is responsible for the production of the flight-or-fight sympathetic hormones epinephrine and norepinephrine. The specialized nerve cells in the medulla are capable of secreting these compounds directly into the circulatory system. Both epinephrine and norepinephrine are peptide hormones that belong to a larger class of molecules known as catecholamines. They will act to increase the activity of body systems necessary for fight-or-flight and decrease activity to those systems for rest-and-digest. Additionally, we would want to make energy more directly available in the form of glucose. Epinephrine can increase the conversion of glycogen back to glucose in both liver and muscle, as well as increase the basal metabolic rate. Both compounds will increase heart and respiratory rate and alter blood flow to supply the systems that would be used in a sympathetic response. This would mean increased blood flow by vasodilation of the arteries leading to the skeletal muscle, heart, lungs, and brain. In addition, vasoconstriction would decrease blood flow to the gut, kidneys, and skin.

Answer 252

Pancreas- The secretions of the exocrine pancreas are components of the pancreatic juice that enters into the duodenum: Amylase (carbohydrate digestion), Lipase (lipid digestion), Trypsin, chymotrypsin, and carboxy-peptidase (protein digestion) islets of Langerhans: alpha, beta, and delta cells. The alpha cells secrete glucagon, the beta cells are responsible for the production of insulin, and delta cells make somatostatin. • Glucagon- secreted in famine- glucose levels run low, the following are stimulated: degradation of protein and fat, conversion of glycogen to glucose, and production of new glucose via gluconeogenesis. In addition to being secreted when triggered by low blood glucose, certain gastrointestinal hormones (e.g., CCK and gastrin) increase glucagon release from the alpha cells. In times of feast, or high glucose levels, secretion will be inhibited. • Insulin- Insulin levels in plasma rise in conjunction with blood glucose levels. Insulin induces muscle and liver cells to take up glucose and store it as glycogen for later use. active when glucose levels are high, insulin stimulates anabolic processes such as fat and protein synthesis. In excess, insulin will cause hypoglycemia, which is characterized by low blood glucose. Underproduction, insufficient secretion, or insensitivity to insulin all can result in diabetes mellitus, which is clinically characterized by hyperglycemia, excess glucose in the blood. excessive glucose in the filtrate will result in its presence in the urine. Since it is an osmotically active particle, its (abnormal) presence in the filtrate leads to excess excretion of water and an increase, sometimes dramatic, of the urine volume. Diabetics often report polyuria, increased frequency of urination, and polydipsia, increased thirst. There are two types of diabetes. Type I (insulin-dependent diabetes mellitus) is caused by autoimmune destruction of the beta cells of the pancreas; these individuals produce little to no insulin, as the majority of beta cells have been destroyed. Type I diabetics require regular injections of insulin to prevent hyperglycemia. Type II (non-insulin-dependent diabetes mellitus) is a result of the body resisting the effects of insulin at its receptor. It is partially inherited and partially due to high-sugar diets • somatostatin- an inhibitor of both insulin and glucagon. High blood glucose and amino acid concentrations stimulate its secretion.

Answer 253

Testes- spermatogenesis- there is a delicate interplay of FSH and LH stimulation on two structures in the testes. FSH stimulates the Sertoli cells and is necessary for sperm maturation, whereas LH causes the interstitial cells to produce testosterone, the major androgen in the male. In addition to being important for spermatogenesis, testosterone is necessary for male embryonic differentiation, male sexual development at puberty, and maintenance of secondary sex characteristics (e.g., axillary and pubic hair). It provides negative feedback to FSH, LH, and GnRH. If the receptors for testosterone are absent from an individual, it cannot exert its effects. The result is a condition called androgen insensitivity syndrome, in which a genetic male (XY) has secondary female sexual characteristics.

Answer 254

* They are also under the control of FSH and LH secreted from the anterior pituitary, which itself is directed by GnRH release from the hypothalamus. The ovaries produce both estrogens and progesterone. * Hormones- estrogen, which is secreted in response to elevated FSH and LH, are responsible for the development and maintenance of secondary female sexual characteristics. They also lead to thickening of the endometrium each month in preparation for implantation of a zygote. In the embryo, they stimulate development of the female reproductive tract. Estrogens are secreted by the ovarian follicles and the corpus luteum. Progesterone- Progesterone is secreted in response to LH stimulation from the anterior pituitary. It is released from the corpus luteum (the remnant follicle on the ovary surface) and is responsible for the development and maintenance (but not generation) of the endometrium. By the end of the first trimester of a pregnancy, progesterone is supplied by the placenta, and the corpus luteum ceases functioning.

Answer 255

Each month after the onset of puberty and until menopause, the endometrial lining will grow and shed in a cyclical manner. This is known as the menstrual cycle. It is controlled by the relative levels of estrogen and progesterone. The menstrual cycle may be divided into four phases: the follicular phase, ovulation, the luteal phase, and menstruation. • Follicular- Follicles mature during the follicular phase (FSH, LH).- menstrual flow, which sheds the uterine lining of the previous cycle, begins. GnRH secretion from the hypothalamus increases in response to the lower levels of estrogen and progesterone, whose concentrations fall off toward the end of each cycle. The higher concentrations of GnRH cause increased secretions of both FSH and LH. These two hormones work in concert to develop several ovarian follicles. The follicles begin to produce estrogen primarily, which at this point has a negative feedback effect and causes the GnRH, LH, and FSH concentrations to level off. Estrogen works to regrow the endometrial lining, stimulating vascularization and glandularization of the decidua. • LH surge at midcycle triggers ovulation.- the developing follicles secrete more and more estrogen. Eventually, estrogen concentrations reach a level that paradoxically results in positive feedback, and GnRH, LH, and FSH levels spike. The surge in LH is important; it induces ovulation, the release of the ovum from the ovary into the abdominal cavity • Ruptured follicle becomes corpus luteum and secretes estrogen and progesterone to build up uterine lining in preparation for implantation; LH and FSH are inhibited.- After ovulation, LH causes the ruptured follicle to form the corpus luteum. The corpus luteum secretes progesterone. From above, we know that although estrogen helps regenerate the uterine lining, it is progesterone that maintains it for implantation. Progesterone levels now begin to rise, while estrogen levels remain high. The very high levels of estrogen and progesterone cause negative feedback on GnRH, FSH, and LH • If fertilization doesn't occur, corpus luteum atrophies, progesterone and estrogen levels decrease, menses occurs, and LH and FSH levels begin to rise again.- If implantation does not occur, human chorionic gonadotropin (hCG, Without hCG to stimulate the corpus luteum, progesterone levels decline, and the uterine lining is sloughed off. The loss of high levels of estrogen and progesterone removes the block on GnRH so that the next cycle can begin.

Answer 256

Pregnancy- If fertilization has occurred, the corpus luteum will be maintained by the presence of hCG, which is secreted by the blastocyst and the developing placenta. During the first trimester of development, it is the estrogen and progesterone secreted by the corpus luteum that keep the uterine lining in place. By the second trimester, hCG levels decline, but progesterone and estrogen rise since they are now secreted by the placenta itself. The high levels of estrogen and progesterone serve as negative feedback mechanisms and prevent further GnRH secretion. • Menopause- results from decreased responsiveness of the ovaries to FSH and LH. Fewer follicles will begin to develop each month, and some may fail to rupture. The decreased response to FSH and LH results in decreased levels of estrogen and progesterone. FSH and LH lose their feedback inhibition, so their plasma concentrations are usually increased in postmenopausal women. Many women report flushing, hot flashes, bloating, headaches, and irritability during menopause as a result of these fluctuating hormone concentrations

Answer 257

The pineal gland is located deep within the brain, where it secretes the hormone melatonin. The actual function of this hormone is unclear, although it is hypothesized that it may be involved in circadian rhythms. The evidence for this is projection of visual information from the eyes to this area of the brain, but the pineal gland is not directly involved in vision.

Answer 258

gastrointestinal tract, glandular tissue can be found in both the stomach and intestine. Many gastrointestinal peptides have been identified, and important ones include secretin, gastrin, and cholecystokinin. he stimulation for release of most of these peptides is food intake.

Answer 259

• The renin-angiotensin-aldosterone system Decreased blood volume causes the juxtaglomerular cells of the kidney to secrete renin, which cleaves an inactive plasma protein, angiotensinogen, to its active form, angiotensin I. Angiotensin I is then converted to angiotensin II which will stimulate the adrenal cortex to secrete aldosterone.

Answer 260

• heart and the thymus. The heart releases atrial natriuretic peptide (ANP) to help regulate salt and water balance. The thymus, located directly behind the breastbone, releases thymosin, which is important for proper T-cell development and differentiation. The thymus atrophies by adulthood

Answer 261

peptide hormones (• Surface receptors • Generally act via secondary messengers. Steroid hormones: • Intracellular receptors • Hormone-receptor binding to DNA promotes transcription of specific genes. • Peptide hormones are made up of amino acids. They range in size from quite small (ADH) to relatively large (insulin). They are all derived from larger precursor polypeptides that are cleaved by posttranslational modifications. these smaller units are transported to the Golgi, site of modification. These modifications activate the hormone and direct it to the correct location in the cell. Such hormones are released by exocytosis after having been packaged into vesicles. • Peptide hormones are charged, so they cannot cross the phospholipid cell membrane and instead bind to receptors on the exterior cell surface. They act as first messengers. Upon binding to their receptors, they stimulate the production of second messengers, such as cyclic AMP (cAMP). This conversion is catalyzed by the enzyme adenylate cyclase. cAMP can then bind to intracellular targets, such as proteins or DNA, to exert the hormone's ultimate effect. The connection between the hormone at the surface and the effect brought about by cAMP within the cell is known as a signaling cascade. At each step, there is the possibility of amplification. One hormone molecule may bind to multiple receptor molecules before it is degraded. Each receptor may activate several adenylate cyclases, each of which will make much cAMP. he actions of cAMP are terminated by phosphodiesterase. effects of peptide hormones are usually shorter lived, because they work through transient second messenger systems. It is quicker to turn them on and off, compared with steroid hormones, but their effects do not last without relatively constant stimulation. ), steroid hormones (all steroid hormones (e.g., aldosterone, estrogen) are derived from cholesterol. Since they are derived from a nonpolar molecule, steroid hormones can easily cross the cell membrane, their receptors are usually intracellular or intranuclear. Upon binding to the receptor, they dimerize (pair up with another receptor-hormone complex). This dimer can then bind directly to DNA and alter its transcription. either increasing or decreasing transcription depending on the hormone and gene in question. The effects of steroid hormones are longer-lived, as they alter the amount of mRNA and protein present in a cell; however, it takes longer to see the effect of steroid hormones, as the processes of transcription and translation are not immediate.), or amino acid-derived hormones ( including epinephrine, norepinephrine, and thyroxine. They are derived from one or two amino acids, usually with a few additional modifications. For example, thyroid hormone is made from tyrosine and includes the addition of several iodine atoms. Depending on the polarity of the molecule, they may either work through second messenger systems the way peptide hormones do (epinephrine falls in this category), or they may actually enter the cell and act like steroid hormones (thyroxine).

Answer 262

a deoxyribose sugar, a nitrogenous base, and a phosphate group. The sugar forms the core to which the other two components are bound. There are four nitrogenous bases in two categories: cytosine (C) and thymine (T) are single-ringed pyrimidines, whereas adenine (A) and guanine (G) are double-ringed purines. CUT the PIE. Cytosine, Uracil, and Thymine are PYrimidines. Adenine and Guanine are purines (PURe As GOLD). Higher G/C content more tightly bound strands. DNA

Answer 263

5′ end of one strand paired with 3′ end of the other strand. • the deoxyribose sugar has both a 3′ -OH and a 5′ -OH group. It gets the name deoxy– because the 2′ position has an – H rather than an – OH. The 3′ group is bound to the 5′ group of the next sugar. The three-dimensional structure of DNA has the polynucleotide backbone formed by the sugars and phosphates, with the nitrogenous bases projecting off to the side.The sugar-phosphate chain is on the outside of the helix, whereas the nitrogenous bases are forced into the middle of the DNA molecule. This allows for base pairing through hydrogen bonding of the nitrogenous base side chains, giving greater stability to the overall molecule. A pairs with T, forming two hydrogen bonds, and C with G, making three hydrogen bonds. a pyrimidine pairs with a purine. one strand has a 5′ → 3′ polarity, whereas its complementary strand has a 3′ → 5′ polarity. The directionality of DNA is one of its most important features; the enzymes that replicate and transcribe DNA can only move 5′ → 3′ . The 5′ end of DNA has an – OH or phosphate group bound to the number 5 carbon of the terminal sugar, while the 3′ end has a – OH on the number 3 carbon of the sugar. The combination of all these properties gives us the Watson-Crick model of DNA. It may be related to transcription, translation, or general base pairing. The bottom line is that DNA and RNA work in a 5′ → 3′ direction The light regions are euchromatin, which is single-copy, genetically active DNA. The dark regions are heterochromatin, which are repetitive sequences that are genetically inactive.

Answer 264

semi-conservative, strand from parent and new daughter strand. * Centromeres– Essential for proper chromosome segregation and the site of kinetochore formation. * Telomeres– Cap the ends of chromosomes, maintaining structural integrity, ensuring complete replication and positioning of the chromosomes. * Origin of replication- 3 billion base pairs- DNA unwinds in multiple places to allow for efficient replication to occur. Each of these points is named an origin of replication. generation of new DNA proceeds in both directions, creating replication forks. When methyl groups are added to strands the methyl groups are added to the new strands.

Answer 265

The most basic unit. The nucleosome consists of 8 histone proteins. DNA is wound almost two times around this protein core to produce a "bead-like" structure. • 30nm chromatin fiber – Nucleosomes are joined by linker DNA and coiled into a 30nm fiber which is organized into loops. This structure is maintained by the histone H1 protein which is attached to the linker DNA. • Loop-Scaffold complex – The loop-scaffold complex provides the compact structure of chromosomes seen during metaphase.

Answer 266

helicase unwinds DNA making single stranded regions, single-stranding binding proteins (SSB) stabilize single strands. As helicase unwinds DNA, it causes positive supercoiling that strains the DNA helix. So DNA gyrase (a topoisomerase) relieves overwound DNA by introducing negative supercoils. Primase, RNA polymerase generates RNA primer TATA box binding to promoter region of gene, several nucleotides long, DNA polymerase is the enzyme responsible for adding the individual nucleotides to the growing strand binding to 3’ end of primer

Answer 267

* 5′ → 3′ direction. A number of different enzymes, collectively referred to as DNA polymerases, catalyze this process. Helicase moves forward, unwinding the DNA helix. SSBs bind to prevent reassociation, and DNA gyrase introduces negative supercoils to prevent torsional strain on the helix. Free nucleotide triphosphates (in the 5′ position) pair with the parent strand, and DNA polymerases cut the phosphodiester linkage to incorporate the new base of hydroxyl group of one nucleotide 3’ and 5’ hydryoxyl group of adjacent nucleotide sugar. Free pyrophosphate (PPi) is also generated. * there will be a 3′ → 5′ strand whose complement will be coded 5′ → 3′ : Leading strand, continually made. NA polymerase can only produce daughter strand DNA in the 5′ → 3′ direction, so small sections known as Okazaki fragments (around 1,000 base pairs) are produced at a time. The primer is introduced as far forward as possible, and then instead of working forward toward the point of the replication fork (which occurs in the leading strand), DNA polymerase works back toward the origin of replication. This strand is known as the lagging strand. Since the replication fork is moving in the other direction, synthesis occurs piecemeal so that the ultimate direction of replication is the same and both new strands can be generated at the same time. leading strand is produced continuously 5′ → 3′ . The lagging strand is produced discontinuously through the formation of Okazaki fragments, which are produced 5′ → 3′ . The summation of Okazaki fragments is in the 3′ → 5′ direction. The small gaps between the Okazaki fragments are also filled with nucleotides, and the sugar phosphate backbone is connected by DNA ligase

Answer 268

* DNA: Double stranded, Sugar = deoxyribose, Base pairing: A/T, G/C, Found in nucleus only * RNA: Single stranded, Sugar = ribose, Base pairing: A/U, G/C, Found in nucleus and cytoplasm. It uses ribose instead of deoxyribose as a sugar, it is usually single stranded, and the base uracil replaces thymine. There are multiple types of RNA, each of which has different functions. RNA is found in both the nucleus and the cytoplasm, where it participates in transcription and translation, respectively. We will discuss four types of RNA: mRNA, tRNA, rRNA, and hnRNA. * MRNA- created during transcription, carries genetic message from nucleus to cytoplasm for translation requires GTP. Eukaryotes- Monocistronic, each mRNA translates into only one produce. prokaryotes, particularly bacteria, messages may be polycistronic, and different proteins can be formed by starting translation at different positions on the mRNA. * tRNA- Once the message arrives at the ribosome, amino acids must be linked into the nascent polypeptide chain. tRNA, found in the cytoplasm, carries out this function. There are 20 amino acids, each of which is indicated by a different codon, so there is a different tRNA for each amino acid. * rRNA- Ribosomal RNA is synthesized in the nucleolus. It forms an integral part of the ribosomes that are used for protein assembly in the cytoplasm. * hnRNA- mRNA precursor, heterogeneous nuclear RNA, which is larger and includes riboproteins in its structure. * Protein synthesis/eukaryotic Transcription- Although the DNA contains the actual coding sequence for a protein, the machinery to generate that protein is in the cytoplasm. DNA cannot leave the nucleus, as it will be quickly degraded, so it must use RNA to transmit its message. The encoding of mRNA is known as transcription. * This template strand is also called the antisense strand because its nucleotide sequence is antiparallel and complementary to the RNA strand produced from it. Like DNA replication, this process can only occur in the 5′ → 3′ direction; it is catalyzed by RNA polymerase. Use uracil instead of thymine, Specialized DNA regions known as promoters signal where to begin transcription. There are also termination sequences, which signal RNA polymerase to dissociate from DNA, thereby stopping transcription. The DNA double helix re-forms, and the newly formed RNA is hnRNA (pre-mRNA). * post-transcriptional processing: (1) a 5′ guanosyl cap must be added to stabilize starting end of transcript , (2) a poly-A tail must be added to protect 3’ end, and (3) introns must be removed Eukaryotic genes contain coding (exons) and noncoding (introns) regions. We want our message to include only the coding regions so that the proper protein will be made. The processing of hnRNA to mRNA occurs in the nucleus. Failure to complete these steps will result in degradation of the pre-mRNA. * Genetic code- degeneracy or redundancy of the genetic code. There are multiple three-letter nucleotide words that can code for the same amino acid. This triplet word is known as a codon. With few exceptions, the genetic code is universal. The genetic code is mostly degenerate for amino acids that are commonly used. Amino acids such as glycine and proline, which are necessary to make collagen, are completely redundant at the third position, whereas those amino acids that are used less commonly may have only one or two coding sequences.

Answer 269

* Translation- conversion from codons to amino acids requiring mRNA, tRNA, ribosomes, amino acids, and energy. The base pairing between the codon and anticodon is both complementary and antiparallel: the 5′ end of the codon lines up with the 3′ end of the anticodon. Be advised that the convention is that both codons and anticodons are always written in 5′ → 3′ order * tRNA- there is nucleotides that are complementary to the codon; they are known as the anticodon. On the opposite pole of the molecule, tRNA is bound to the amino acid that corresponds to the codon in question. Each tRNA has a CCA nucleotide sequence where the amino acid binds. Each tRNA has a helper tRNA synthetase, an enzyme that binds the amino acid to the tRNA using GTP. The result is an aminoacyl-tRNA complex. * Ribosomes- large and small subunit, and they only bind together during protein synthesis consisting of ribosomal proteins and rRNA. 3 binding sites- One are for the mRNA; the other two are for the tRNA. The binding sites for tRNA are the A site, which holds the aminoacyl-tRNA complex, and the P site, which binds to the tRNA attached to the growing polypeptide chain. * Polypeptide synthesis- requisite components into initiation, elongation, and termination * initiation- Synthesis begins with mRNA seeking out a small ribosome. They bind in the presence of initiation factors, and the small ribosome slides along the mRNA until it reaches a start codon (AUG). The initiation aminoacyl-tRNA complex, methionine tRNA (with the anticodon 5′ -CAU-3′ ), base pairs with the start codon. At this point, the large ribosomal subunit joins the complex, completing the ribosome. The tRNA is in the P site at this point, because it is a part (and the only part) of the growing polypeptide chain. * Elongation- complex allows ribosome to slide along mRNA adding new amino acids, Hydrogen bonds form between the mRNA codon in the A site and the complementary tRNA anticodon. This fills the A site. We now have a charged aminoacyl-tRNA in both the A site and the P site. The enzyme, peptidyl transferase, uses the energy that was stored in the amino-acyl-tRNA complex when the amino acid was loaded (remember, this was from GTP) to catalyze the formation of a peptide bond. The aminoacyl-tRNA used for this is the one in the P site. The bond is made between the single amino acid in the A site and the methionine in the P site. Now the tRNA in the P site is free, and there is still an aminoacyl-tRNA in the A site. This aminoacyl-tRNA has its own amino acid, which is now bound to a methionine. Translocation is necessary to add the next amino acid residue. The ribosomal assembly slides in a 5′ → 3′ direction along the mRNA. This moves the next codon into place in the A site. At the same time, the uncharged tRNA in the P site is expelled, and the aminoacyl-tRNA that is carrying our nascent chain is moved from the A site to P site. The process is ready to begin again with an empty A site * Termination- If the codon in the A site is UGA, UAA, or UAG, it is known as a termination codon. Instead of a new aminoacyl-tRNA binding to the A site, a protein called release factor binds to the termination codon, causing a water molecule to be added to the polypeptide chain. The polypeptide chain will then be released from the tRNA in the P site, and the two ribosomal subunits will dissociate. To save time, as well as increase the amount of protein that may be made from a single transcript, several ribosomes may translate a message at the same time. This is known as a polyribosome. * Post-translational modifications- including folding into secondary structure with lowest energy conformation. Polypeptide cleaved or sugars added, phosphorylation, carboxylation, and methylation for targeting. * 5′ → 3′: DNA→ DNA = replication: New DNA synthesized in 5′ → 3′ ./ DNA→ RNA = transcription: New RNA synthesized in 5′ → 3′ direction./ RNA→ protein = translation: mRNA read in 5′ → 3′ direction

Answer 270

• mutations- increasing genetic diversity/ base pair mutations, base pair insertions, or base pair deletions. Base pair mutations are also called point mutations, one base pair is substituted for another Transition – substitution of a pyrimidine (C or T) by another pyrimidine, or of a purine (A or G) by another purine • Transversion – substitution of a pyrimidine by a purine or of a purine by a pyrimidine • whereas insertions (can include transposition where a sequence is inserted in an incorrect location in the DNA) and deletions are both also known as frame shift mutations. • Point mutations- single nucleotide residue, depending upon location… no effect (noncoding or coding?), highly detrimental (sickle cell). Coding- no effect silent mutations, degenerate genetic code. he final nucleotide could be A, C, U, or G, so a “ mutation” in this position would be irrelevant. Thus, a mutation at this nucleotide position will have no effect. Changes in either the second or first nucleotide can be more detrimental. A point mutation at the first or second position in the codon may result in a missense mutation in which one amino acid is substituted for another. A nonsense mutation is a mutation that produces a premature termination of the polypeptide chain by changing one of the codons to a stop codon. Nonsense mutations can have disastrous effects. • Frame shift- codons of 3 nucleotides=reading frame. Insertion or deletion of nucleotides will shift the reading frame, usually resulting in either changes in the amino acid sequence or premature truncation of the protein (due to the generation of a nonsense mutation). The effects are usually much more serious than a base pair substitution.

Answer 271

* Chromosome abnormalities: constitutional– the abnormality is found in all cells of the body, or somatic (acquired) – the abnormality is found only in certain cells or tissues. * Numerical– The gain or loss of complete chromosomes * Aneuploidy – One or more chromosomes are missing or are present in more than the normal number. Aneuploidy usually results from nondisjunction, which is the failure of paired chromosomes to separate in anaphase (usually during meiosis I). * Monosomy – The loss of a single chromosome/ Autosomal monosomy is always lethal (Monosomy of sex chromosome X results in Turner’ s Syndrome (45, X)) * Trisomy – The gain of an extra chromosome (Down Syndrome (Trisomy 21)) * Tetrasomy – The gain of an extra pair of homologous chromosomes (Tetrasomy 9p, Tetrasomy 18p) * Euploidy – An extra, complete set of chromosomes is present or missing (Polyploidy – More than two sets of chromosomes are present, Triploid, tetraploid, pentaploid, etc., Monoploidy – A complete chromosome set is missing/ Lethal) * MixoploidyMosaicism – Two or more genetically different cell lines within a single individual derived from a single zygote * Chimerism – Two or more genetically different cell lines within a single individual derived from different zygotes * Structural– The formation of abnormal chromosomes through the misrepair of chromosome breaks or a malfunction during recombination part of a chromosome is duplicated, deleted, or has been switched to another part of the chromosome. Therefore, the chromosomal number is normal but there is either an excess or deficiency in the genetic material present in the cell. There are two main ways that structural abnormalities arise by Recombination malfunction or Misrepair of chromosome breaks resulting in * Inversions – the chromosome segment is rejoined opposite of its normal configuration without loss of genetic information * Duplication – a segment of the chromosome is repeated * Deletion – a segment of the chromosome is lost * Translocation – chromosomal material is exchanged between non-homologous chromosomes * Reciprocal – there is no loss of genetic information although gene arrangement is altered (considered a balanced translocation) * Robertsonian – the short arm of two chromosomes breaks off and the long arms are fused together; this can result in a balanced translocation or an unbalanced translocation in which genetic material is gained or lost Molecular pathology focuses on the effect of a genetic mutation on the gene product and the effect that this in turn has on the phenotype. One classification of mutations is by their effects, either through the reduced or loss of function of a gene product or the gain of function of a gene product.

Answer 272

* Loss of function(– the gene product, this can be the RNA or protein product, has reduced (leaky mutation) or no (null mutation) function * Typically these are recessive phenotypes – if one allele is mutated and loses function, the normal allele can usually produce enough gene product to prevent the disease phenotype and the disease results when both alleles are mutated. If the normal allele cannot compensate for the lost gene product a dominant mutation will result * Point mutations, frameshifts, and splicing mutations can all lead to the loss of function of a gene product. The same phenotype can result from many different mutations * Epigenetic modifications can result in loss of function without altering the DNA sequence. DNA methylation of control sequences can silence the corresponding gene/ Translocations that rearrange genes may alter the transcription of normal genes. Alterations of protein conformation can lead to loss of function * Cystic fibrosis- caused by loss of function mutations in the CFTR gene and it is the most common lethal genetic disease in the U.S. The normal gene codes for a membrane protein that transports chloride ions in and out of cells. This has the greatest effect on the epithelial cells lining organs and it is particularly evident in the lining of the lungs. Normally one channel allows sodium into the cells of the lining while another channel controls the outward flow of chloride ions. If a chloride channel is defective or absent chloride ions are not removed from the cell, and consequently water does not flow out of the cell into the mucus of the linings. This disrupts the normal balance of salt and water and results in the buildup of airway secretions.) and Gain of function • results from over-expression of a gene product, a new function for a gene product, or expression in the incorrect location of a gene product • Typically are dominant phenotypes – the presence of one normal allele cannot mask or prevent the over production or abnormal behavior of the mutated allele • Often involves a product signaling inappropriately or failing to terminate a normal process • Mutations that cause gain of function are much more specific than those that cause loss of function. The same phenotype typically only results from one or two specific mutations (mutational homogeneity). Results in the "Founder Effect" where a disease is typically seen only within a certain population reflecting a mutation found only in the founders of the present population. Mutations that produce a new function for a gene are rare among inherited disease but common in cancer. Non-mutant versions of genes that control cell proliferation are known as proto-oncogenes. A mutation that results in a gain of function can alter the gene to become an oncogene, which is excessively active and causes cellular hyperproliferation - the basis of cancer. Only one mutant allele is necessary to affect the function of the cell. Oncogenes can be activated through: • Amplification – hundreds of extra copies of a gene may be present • Point mutations – can lead to excessive cellular response • Chromosomal translocations – a novel gene is created. Philadelphia chromosome results in myeloid leukemia • Transposition – a gene is moved from a relatively inactive area of chromatin to an active area where it is consequently transcribed in abnormal amounts • Tumor suppressor genes inhibit pathways that lead to cancer. A mutation in a tumor suppressor gene causes a loss of function of the tumor suppressor gene product which can result in cancer. Both copies of an allele must experience loss of function in order for the function of the cell to be affected. Loss of function in a tumor suppressor gene can occur through: • Deletion of a portion of chromosome containing the gene • A point mutation within the DNA sequence of the gene • Methylation of DNA that prevents the tumor suppressor gene from being transcribed • Huntington’s Disease- results from a gain of function mutation that produces an autosomal dominant disorder characterized by neurodegeneration. Other phenotypic manifestations are uncontrollable movements, personality alterations and memory loss. The typical onset of HD is not until 35-40 years of age. HD is caused by the expansion of a triplet repeat, which is a set of three nucleotides (CAG) that code for glutamine. This mutation causes more glutamines to be inserted in the protein product which appears to cause the product to form a new function which ultimately leads to cell death, particularly in the nervous system

Answer 273

* DNA polymerase mistakes at low rate, ionizing radiation damage DNA, or DNA self-damage, Elements known as transposons can remove and insert themselves into the genome. If they insert in the middle of a coding sequence, the gene will be disrupted. Spontaneous deamination (cytosine loses amino group to form uracil or alkylation of bases addition of a methyl group to base, light causing formation of thymine dimers, ionizing radiation producing double strand breaks, chemicals causing formation of bulky adducts, * Direct Repair reverses DNA damage without cutting the deoxyribose phosphate backbone (e.g. removing a methyl group in order to restore the original base). * Base Excision Repair (BER) is used when incorrect bases are present in DNA (e.g. U is incorporated into DNA). The damaged base is recognized by a glycosylase and is hydrolytically removed from the deoxyribose phosphate backbone. This leaves an apurinic or apyrimidic site where the purine or pyrimidine was removed. The correct base is then inserted and the break is sealed by DNA ligase. * Mismatch Repairs use a method similar to BER to remedy incorrect pairings of the normal bases (e.g. A paired with C or G will be repaired so that A pairs with T and C pairs with G). * Nucleotide Excision Repair (NER) removes thymine dimers and bulky adducts. The area of DNA surrounding and including the damaged portion is unwound and an endonuclease makes cuts on both the 5’ and 3’ sides of the damage. The bases are removed by an exonuclease and DNA is resynthesized, using the sister strand as a template to fill the gap. DNA ligase seals the new section into the backbone. * Post-replication Repair is used to repair double strand breaks. This involves a type of recombinational repair in which a single strand of DNA from a homologous chromosome is used to resynthesize the missing portion. Broken ends can also be rejoined directly and ligated together. However, the original sequence is not always maintained and mutations such as translocations can offen occur as a result of this. * Gene therapy- if the affected gene can be identified for a particular disorder the malfunction can be corrected through molecular manipulation. There are four approaches to gene therapy: * Inserting a normal gene into the genome to replace a nonfunctional gene * Replacing a nonfunctional gene through homologous recombination * Repairing the mutant gene by reversing the original mutation * Altering the regulation of a gene

Answer 274

• gene expression in eukaryotes is at the level of transcription. The ultimate product of a gene is a protein, and the first costly step in protein synthesis is transcription, therefore it is more economical to control gene expression at the level of transcription. There are two types of control that occur at this level: Negative control (or repression) – A protein binds to DNA in order to interfere with the binding of the RNA polymerase to the promoter region. This prevents transcription. And Positive control (or activation) – A protein binds to DNA in order to facilitate the binding of the RNA polymerase to the promoter region. This initiates transcription. • The formation of an active protein product can also be modified or controlled at various points along the pathway including: • mRNA processing and modification Alternate splicing can form different gene products Capping and Poly A tails • RNA transport out of the nucleus • Transcript stability ◦ Certain transcripts have sequences that code for rapid degradation • Translational initiation • Post-translation modification • Protein transport • Protein stability

Answer 275

* Viruses- not alive genetic material and capable to make proteins only when using other’s machinery. Depending upon virus either insert DNA or everything etc.. * Viral genetics- few genes-several hundred. DNA/RNA, single/double stranded. Infection- Viruses may only infect cells that have receptors that recognize the viruses' protein coat (capsid). * DNA-containing virus replication- enters the nucleus and makes use of the DNA and RNA polymerases found there without extra work. A few DNA viruses carry out replication in the cytoplasm. These viruses must bring their own DNA and RNA polymerases with them because the host's are restricted to the nucleus, which these particular viruses never enter. * RNA-containing virus replication- cells no enzymes to replicate RNA. Virus brings RNA replicase or wait for enzyme translates from genome by acting as mRNA. Retroviruses- creates a DNA copy from RNA using an enzyme called reverse transcriptase. Creates DNA from RNA, integrate newly synthesized DNA into host genome like HIV. * Translation & progeny release - ribosomes, tRNA, amino acids, and enzymes of the host, the transcribed genes are now translated into protein. These proteins are usually structural and allow for creation of new viral particles (virions). Lyse because of filled with viral particles, initiating apoptosis releasing viral progeny. When a virus instead leaves the cell by fusing with its plasma membrane, the process is known as extrusion. It is similar to budding and allows the virus to keep the host cell alive. A virus in this state is said to be in a productive cycle

Answer 276

• bacteriophages- viruses targeting bacteria keep viral envelope etc. outside, insert DNA into hole in bacteria surface. polyhedral head and a tail apparatus with tail fibers at the end. The bacteriophage attaches to a host cell by means of the tail fibers. A bacteriophage infects a host cell by attaching to it, releasing enzymes that create a hole in the bacterial cell wall, and then injecting its DNA into the bacterial host cell Virus lytic- virus makes maximal use of cell’s machinery while damaging, once host swollen with virions, cell lyses and other bacteria infected with bacteria bacteriophage takes control of the host cell's genetic machinery. The viral DNA is translated and transcribed, and new phages are assembled. The bacteriophage directs production of an enzyme that digests the bacterial cell wall. Due to the weakened cell wall and the increased intracellular pressure from the newly replicated viral particles, the bacterial cell burst. virulent/lysogenic- integrate into host genome bacteria in prophage form, reproduce virus will continue separate from host genome and go into lytic cycle. virus may remain indefinitely integrated into the host genome, at some point dormant , environmental factors (radiation, light, or chemicals) will cause the provirus to leave the genome and revert to a lytic cycle. Can be deadly to bacteria there may be some benefit to having them integrated in the lysogenic cycle. Infection with one strain of phage generally makes the bacteria less susceptible to other phages (superinfection). Since the provirus is relatively innocuous, there may be some evolutionary advantage to this association.

Answer 277

* Bacterial genome- prokaryotes single-celled organisms containing a circular DNA genome and no membrane-bound organelles. The genome localizes to the nucleoid region of the cell. extrachromosomal material known as plasmids. These are a way for bacteria to gain antibiotic resistance. specialized subset of plasmids known as episomes are capable of integrating into the genome. the two processes are not physically separate transcription and translation occurs almost simultaneously with mRNA being able to translate into multiple proteins. * Replication- one origin of replication, in both directions very quickly 500 bp/sec. 4.5million bp * genetic variance- favorable growth- bacteria utilize binary fission, asexual increasing numbers rapidly, daughter cell genetically identical. To increase genetic diversity: transformation, conjugation, and transduction.

Answer 278

* Transformation- results from the integration of a foreign chromosome fragment (plasmid) into the host genome. The result is a bacterium that is genetically unique from the original cell and any daughter cells that it produced before adding the plasmid to its genome. * Conjugation- two cells forming a cytoplasmic bridge between them that allows for the transfer of genetic material. transfer is one way, from the donor male (+) to the recipient female (− ). The bridge is made from appendages called sex pili that are found on the donor male temporary. To form the pili, bacteria must contain plasmids known as sex factors, can be plasmid or pheromone. Ex E coli Bacteria possessing this plasmid are termed F+ cells; those without it are called F– cells. During conjugation between an F+ and an F– cell, the F+ cell replicates its F factor and donates the copy to the recipient, converting it to an F+ cell. Plasmids that do not induce pili formation may transfer into the recipient cell along with the sex factor. Plasmid integrated into host genome. The sex factor is a plasmid, but through processes such as transformation, it can become integrated into the host genome. In this case, when conjugation occurs, the entire genome replicates since it now contains the sex factor. The donor cell will then attempt to transfer its entire genome into the recipient. Usually the bridge collapses before the full DNA sequence can be moved. conjugation bridge usually breaks before the entire chromosome is transferred, but the bacterial genes that enter the recipient cell can easily recombine with the bacterial genes already present to form novel genetic combinations. Hfr for high frequency of recombination used to figure out gene order as F inserts to bacteria at certain and same spot. * Transduction- bacteriophages integrate into host, not perfect excision remove from chromosome and take genes with them, infecting new bacteria integrating into new genome. Bacterial genes transferred from one cell to another by a virus. In generalized transduction, DNA from any part of the host's chromosome becomes a part of the viral genome, replacing the viral genome. In specialized transduction, DNA from a specific part of the host's chromosome becomes part of the viral genome, usually replacing some viral genes. * Trp operon- enzyme catalyzed reaction binding to repressor in turn binds to operator to prevent further transcription of enzyme. transcription norm as long as no co-repressor present. Co-repressor binds to repressor forming a complex that binds to operator and prevents transcription.

Answer 279

* Prokaryotes gene regulation- regulate transcriptional level- ability to transcribe a gene is based on RNA polymerase's access to the genome. Operons direct this process by being clustered groups of genes that perform a related or coordinated function. They are made up of structural genes, an operator gene, and a promoter gene/region where RNA polymerase binds to initiate transcriiption. structural gene codes for the protein of interest— for example, lactase, an enzyme that digests the disaccharide lactose. Next is the operator site, where a repressor protein can attach to prevent transcription. It consists of a nontranscribable region of DNA that is capable of binding a repressor protein. The promoter site is similar in function eukaryotes: It provides a place for RNA polymerase to bind. The sequence farthest to the left codes for a protein known as the repressor. This protein can bind to the operator sequence and acts as a roadblock. RNA polymerase cannot get from the promoter to the structural gene because the operator region has a giant repressor in the way. inducible and repressible. Inducible systems require the presence of a compound known as an inducer to cause transcription of the structural gene. Repressible systems are the opposite. transcribing unless a corepresssor is present. Repressor made, binding tightly to operator sequence preventing transcription of structural gene. remove the block, an inducer must bind the repressor protein so that RNA polymerase can move down the gene. raise the level of inducer, more of the repressor will be bound to it, rather than to the operator sequence. The genes are transcribed together to form polycistronic RNA which codes for multiple protein products. As in eukaryotic control, transcription is initiated through the interaction of accessory proteins which act as activators. It is inhibited by the interaction of inhibitory proteins that act as repressors. Lac operon- when lactose high and glucose low. * Repressible- repressible systems allow constant production of a protein product. repressor made by the regulator region is inactive until it binds to a corepressor. The complex can then bind to the operator region and prevent further transcription. Negative feedback.- final structural product corepressor. Levels higher bind to repressor and complex attach to operator region preventing further transcription of same gene.

Answer 280

* PCR- selectively amplify target RNA, requires DNA amplified, primers, DNA polymerase, and dNTPs added. * Heating the original DNA strand in order to denature (94º C) the DNA; this produces two complimentary single strands of DNA * Annealing (54º C) primers to the single stranded DNA; the specific single stranded primers that are used attach to the complimentary portion of single stranded DNA * DNA polymerase attaches to the primer/DNA complex and moves down the DNA chain reading the template strand and adding the appropriate complimentary base (dNTP); this extension (72º C) produces a new double stranded DNA molecule from each strand of the original DNA causing an exponential increase in the number of copies of a particular gene * DNA sequencinguses template DNA, free nucleotides dNTPs, and polymerase to undergo denaturing, annealing, and replication as well as dideoxynucleotides ddNTPs which lack a hydroxyl group at the 3’ position, as well as dNTPs. Therefore the addition of one of the ddNTPs to the growing chain will terminate chain elongation since no further nucleotides can be added without the 3’ hydroxyl group. if a strand were replicated in the presence of deoxy-C and a small amount of dideoxy-C, most of the time a normal C will be incorporated. Dideoxy-C will randomly be incorporated leaving a dead-end product. Eventually all copies being made will be terminated by a dideoxy-C and with millions of starts there will be strands stopping at every possible C. In this case all of the strands will have a common 5’ end and variable 3’ ends that all stop at a particular C in the chain. Labeled with fluorescence resulting fragments are subjected to polyacrylamide gel electrophoresis and therefore are separated by size. This sequence can be read from top to bottom.

Answer 281

process of adaptation and change leading to genetic diversity and new life forms. Accomplished by natural selection, mutation, genetic drift, and genetic shift.

Answer 282

use and disuse generation of new species form older ones. Organs used extensively develop, not used- atrophy. Acquired characteristics- emergence of new, more complex species.

Answer 283

1. Organisms produce offspring, few of which survive to reproductive maturity. 2. Chance variations within individuals in a population may be inheritable. If these variations give an organism a slight survival advantage, they are termed favorable. •3. Individuals with a greater preponderance of these favorable variations are more likely to survive to reproductive age and produce offspring; the overall result will be an increase in these traits in future generations. •This process is known as natural selection. Over long periods of time, aggregations of these favorable traits will result in the separation of organisms into distinct species. Fitness is defined as the reproductive success of an individual. Reproductive success is directly related to the relative genetic contribution of an individual to the next generation •natural selection is simply a mechanism for evolution. Natural selection is equivalent to survival of the fittest. Natural selection:

Answer 284

due to mutation and recombination. •If the variation is “ selected for” by the environment, that individual will be more “ fit” and more likely to survive to reproductive age. •Survival of the fittest leads to an increase of those favorable genes in the gene pool. •Neo-Darwinism/modern synthesis- mutation or recombination results in a change that is favorable to the organism's survival, that change is more likely to pass on to the next generation; the opposite is also true. This process is termed differential reproduction. After time, those traits passed on by the more successful organisms will become pervasive in the gene pool. The gene pool is the sum total of all genes from all individuals in the population at a given time. Because it is the gene pool that changes over time, we must be careful to say that populations, not individuals or species, evolve.

Answer 285

Niles Eldredge & Stephen Jay Gould, little evolution within a lineage of related forms occur over long periods of time, followed by massive burst. Change in some species occur in rapid bursts rather than evenly over time

Answer 286

* explains origins of species. Evidence in paleontology, biogeography, comparative anatomy, comparative embryology, and molecular biology. * Paleontology- relating the ages of different fossils to their anatomies and relative abundances, paleontologists can determine the chronological succession of species in the fossil record. * Biogeography- evolution does not occur equally in all places around globe. He hypothesized that these animals and plants must have migrated to the island and then evolved in isolation from one another, thereby leading to species divergence. * Comparative anatomy- Homologous structures are similar in structure and share a common evolutionary origin, even if they don't have a similar appearance, shape, or form. Ex. Bat wings, whales’ flippers homologous structural precursor in common ancestor of animals forearm structures * analogous structures- serve common purpose but evolved separately in species. Species benefited from flight by natural selection and developed unique mechanisms to achieve flight. * Vestigial structures- remnants of organs lost ancestral functions. Coccyx/tailbone no longer tail for balance, appendix not necessarily. * Comparative embryology- analyzing similarities between embryos of different species, tail present as tail during human embryogenesis, gills in all chordates fish, bird etc. * molecular biology- comparing DNA sequence between different species predicting degrees of similarity between two organisms. As species become more taxonomically distant, the amount of shared genome will decrease. One way of indirectly comparing DNA sequences is by comparing protein structures * genetic basis of evolution- selecting variations more favorable generated by mutations random base changes in DNA sequence, recombination etc.

Answer 287

hardy- Weinberg equilibrium- how often allele appears in population- gene frequency with evolution resulting from changes in these gene frequencies in reproducing population over time. When the gene frequencies of a population are not changing, the gene pool is stable, and no evolution is occurring. Five criteria must be met for this to be true. 1. The population is very large. 2. There are no mutations that affect the gene pool. 3. Mating between individuals in the population is random. 4. There is no net migration of individuals into or out of the population. 5. The genes in the population are all equally successful at reproducing. • gene as having only two possible alleles, T and t. p is the frequency of the dominant allele T and q is the frequency of the recessive allele t. There are only two possible choices at the gene locus, so p + q = 1, or the frequency of alleles in the population, because the combined frequency of the alleles must total 100 percent. We can square both sides of the equation to get (p + q)2 = 12. Expanding the binomial on the left, we derive a second equation: frequency phenotype in population. Where p2 = frequency of TT (dominant homozygotes) 2pq = frequency of Tt (heterozygotes) q2 = frequency of tt (recessive homozygotes) • twice as many alleles as individuals- mircoeveulation not occurring in population gene frequency remain constant from generation to generation.

Answer 288

* Microevolution- rules violated, mutations 1/10million bp DNA replication. * Natural selection- genotypes with favorable variations selected through natural selection, frequency of favorable genes increase within gene pool, faster wings selected for * mutation- Gene mutations change allele frequencies in a population, shifting gene equilibrium. * Assertive mating- mates chosen by phenotype and proximity not random so genotypes affected departing from predictions. * Genetic drift- changes in composition of gene pool by chance pronounced in small populations, founder effect, reproductive isolation by natural barriers or catastrophe * genetic flow-migration of individuals between populations resulting in loss or gain of genes and change in composition of populations gene pool

Answer 289

* Modes of natural selection- method capable of generating stable evolutionary changes over long periods of time, occur by stabilizing selection, directional selection, or disruptive selection * stabilizing selection- keep phenotypes within a specific range by eliminating extremes. Birth weights within narrow range too little not healthy enough to big complications * directional selection- adaptive pressures leading to emergence and dominance of initially extreme phenotype, bacteria resistant to penicillin or die. * Disruptive selection- both extreme phenotypes selected over norm, beak sizes large or small * altruistic behavior- insects bees and ants, certain individuals endure sacrifice to benefit other large castes of workers sterile for benefit of whole colony. Group selection…- purpose preventing reproduction not passed along. Kin selection- organisms behaving if closely related to successfully reproducing organisms and Neo-Darwinism. Inclusive fitness- number of alleles individual passes on to next generation even only indirectly.

Answer 290

Speciation- emergence of new species, group of individuals can interbreed freely with each other but not members of other species, separated geographically for long period of time different evolutionary pressure leading to different adaptive selections. Changes lead to reproductive isolation- two groups separate species prezygotically-( prevents formation of zygote completely) or postzyogtically (gamete fusion but inviable or infertile offspring) • prezygotic isolation mechanisms: temporal isolation- Two species may breed during different seasons or times of the day, thus preventing interbreeding. Ecological Isolation- Two species live in the same territory but in different habitats. They rarely meet and, therefore, rarely mate. Behavioral Isolation- Members of two species are not sexually attracted to each other because of differences in such things as pheromones (chemical signals) and courtship displays. Reproductive Isolation- The genitalia of two species are incompatible, so interbreeding cannot occur. Gametic Isolation- Intercourse can occur, but fertilization cannot. Postzygotic isolating mechanisms: Hybrid Inviability- Genetic incompatibilities between two species abort hybrid zygote development, even if fertilization does occur. Hybrid Sterility- Hybrid offspring are sterile and thus incapable of producing functional gametes. Hybrid Breakdown- First-generation hybrids are viable and fertile, but second-generation hybrid offspring are inviable and/or infertile. The potential for hybrid breakdown exists whenever closely related but reproductively isolated species are introduced to each other, and it occurs more in plants than in animals. • Adaptive radiation- single ancestral species given rise to number of different species, each species diverges to point that able to occupy unique ecological niche decreasing competition for limited resources.

Answer 291

* Patterns of evolution- similarities between species, sharing common ancestor or environment with same evolutionary pressures? three patterns of evolution emerge: convergent evolution, divergent evolution, and parallel evolution * convergent evolution- independent development of similar characteristics in two of more lineages not sharing a recent common ancestor. Fish and dolphins resemble evolving certain feature adapting to conditions of aquatic life * divergent evolution- independent development of dissimilar characteristics in two or more lineages sharing common ancestry, seals and cats mammals order carnivore different in appearance different environments and adapted to diff pressures. * parallel evolution- Parallel evolution refers to the process whereby related species evolve in similar ways for a long period of time in response to analogous environmental selection pressures.

Answer 292

Oparin and Haldane earliest life in stromatolites, evidence of photosynthetic bacteria 3.5 bya, primitive • Formation of organic molecules- high amounts of carbon, hydrogen, and nitrogen with lesser oxygen. Mixture in seas- primordial soup. massive energy input from many sources, including the sun, lightning, radioactive decay, and volcanic activity, bonds formed between these atoms. Miller- Miller carried out an experiment in which he mixed these gases and exposed them to an electrical discharge. 20 simple amino acids, lipids, 5 nitrogenous bases of DNA and RNA were found in the reaction apparatus. • Formation of protobionts- lab experiments produced polymers assembled spontaneously into tiny proteinaceous droplets of microspheres, selective permeable membrane separating them from surrounding maintaining internal environment. Colloidal droplets, coacervates polypeptides, nucleic acids, and polysaccharides capable of carrying out enzymatic activity within membrane if enzymes and substrate present, but not living cells grow in size and divide organic polymers primitive ancestors, protobionts. • Formation of genetic material- believed that short strands of RNA were the first molecules capable of self-replication and of storing and transmitting information from one generation to the next. free bases can align with their complementary bases on a short RNA sequence and bind together, creating a new short RNA chain. Natural selection probably favored RNA sequences whose three-dimensional conformations were more stable and could replicate faster. The next evolutionary step may have involved the association of specific amino acids with specific RNA bases. Thus, an RNA sequence could bring a number of amino acids together in a particular sequence and facilitate their bonding to form a particular peptide. Natural selection may also have selected for the synthesis of those peptides that enhanced the replication and/or the further activity of the RNA. Once this hereditary mechanism developed, protobionts would have been able to grow, split, and transmit important genetic information to their progeny. Self-replicating molecules eventually evolved to code for many of the molecules needed by primitive cells. Evolutionary trends then led to the eventual establishment of DNA, which is a more stable molecule than RNA, as the primary warehouse of genetic information.

Answer 293

intercellular junctions: tight (membrane of neighboring cells attached, bound no material pass between cells or past junctions, total barrier for transport and diffusion, small intestines), anchoring (cells subject to mechanical stress desmosomes attach epithelial to skin), and gap junctions (direct connection of cytoplasm of one cell and plasma of neighboring via channels, formed by connexn in heart

Answer 294

site of secretion is pancreas activates zymogens: trypsinogen to trypsin chymotrypsinogen to chymotrypsin carboxypeptidase secreted as zymogen and activated by trypsin

Answer 295

it hydrolyzes specific peptide bonds and its site of secretion is the pancreas activated by enterokinase activates carboxypeptidase

Answer 296

hydrolyzes lactose to glucose and galactose intestinal glands

Answer 297

hydrolyzes starch to maltose

Answer 298

hydrolyzes lipids produced in pancreas and secreted by small intestine

Answer 299

created in the liver and stored in the gallbladder emulsifies fats

Answer 300

secreted by the intestinal glands hydrolyzing sucrose to glucose and fructose

Answer 301

from chymotrypsinogen by enterokinase acts in small intestine

Answer 302

large fatty acids and glycerol form triglycerides, phosphoglycerides forming micron absorbs into lacteals

Answer 303

starch to maltose pancreatic and mouth

Answer 304

cleavage of amino acids from the amino terminus of the protein intestine

Answer 305

catalyzes hydrolysis of maltose to glucose | intestine

Answer 306

terminal peptide bond at carboxyl end pancreas produced

Answer 307

it decreases blood pressure

Answer 308

sympathetic activtity, increased heart rate, increased blood pressure because of vasopressin constricting blood vessels, dilating arterioles increasing blood flow to body not digestive, ADH decreases urine volume increasing water reabsorption in collecting duct

Answer 309

exhaustive methylation of the amine to the quaternary ammonium compound followed by elimination to get a carbon carbon double bond and fully methylated amine with amine originally cleaved bond

Answer 310

lowers heart rate, promoting digestion, decrease blood pressure increase HCL production

Answer 311

increase in arterial pressure, decrease in renin production and a consequent decrease in aldosterone secretion, decrease aldosterone secretion decreases sodium reabsorption by reabsorbing water, decreasing reabsorption of water increases water excretion reduce blood pressure

Answer 312

sugars that differ in the configuration about a single stereo center,

Answer 313

differ in configuration about new stereo center formed when they adopt a ring configuration

Answer 314

reduces a carbonyl group to the corresponding alkane, two step reaction involving hydrazine's forming hydrazine or C=NNH2, second step basic solution creating nitrogen gas and a hydrocarbon formation

Answer 315

five-membered ruby firmed through attack by the hydroxyl oxygen of C-4, with a furanose a fiv remembered ring

Answer 316

six membered ring energetically favorable

Answer 317

cyclic ester

Answer 318

sugar acetal, formed during polysaccharide formation, formed by exposing D-glucose to an alcohol in acidic environment

Answer 319

corpus luteum or placenta

Answer 320

LH secretion increase because of positive feedback on hypothalamus, GnRh secretion will increase from positive feedback

Answer 321

Increased heart rate, increased respiration rate to inhale more air than normal in order to compensate for air having less oxygen, increased tidal volume increasing minute volume or the amount of air inhaled and exhaled in a minute, increased concentration go erythropoietin in the blood to increase erythrocytes in the blood and increase oxygen capacity

Answer 322

cell=hypotonic to pure water, Hypotonic, then, would be if a cell with, say, salt and water is placed in a pure water environment. Water would rush into the cell due to osmotic pressure.

Answer 323

cell=hypertonic to saltwater, a cell filled with water and place it in a mixture of water and, say, salt. The cell will be hypertonic because water will flow from the cell to the salt solution. In other words, hypertonicity is when a higher concentration of solutes outside the cell causes water to leave the cell via osmosis.

Answer 324

CO2 exhalation increased to decrease CO2/HCO3 concentration

Answer 325

in response to excess amino acids promoting release of glucagon to increase blood glucose promoting gluconeogenesis , glucose can be made from amino acids through gluconeogenesis, glucagon also promotes formation of ketone bodies from fatty acids, degrades glycogen, protein synthesis halted when low blood glucose

Answer 326

proteins undergo transanimation to utilize protein molecules for energy converting amino acids into molecules suitable for TCA cycle, beta oxidation of fats carbon chain of lipid broken down two at a time, entering TCA cycle

Biology MCAT Flashcards

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