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Flashcards in Biology 4 Deck (68):

Digestive System

Physical & chemical digestion
Breakdown of all nutrient macromolecules into their monomers is done via HYDROLYSIS



Saliva provides lubrication & alpha-amylase (enzyme). Chemical digestion of carbohydrates.



U-shaped flap of cartilage and membrane
Disallows food down the trachea, only allows food down to the esophagus.
Straight up when in "default position"



Food storage, mixing
First site of protein digestion, which is done via hydrolysis by the enzyme PEPSIN, which begins as PEPSINOGEN, a ZYMOGEN precursor


Four Stomach Lining Cell types

1) Mucous Neck Cells: make and secrete mucus into gastric pits. Secreted mucus is alkaline, which provides protection due to the acidity of the stomach. (NOT GOBLET CELLS)

2) Chef Cells: make and secrete zymogen pepsinogen (into gastric pits/stomach lumen)

3)Parietal Cells: Secrete HCl (into gastric pits/stomach lumen). Responsible for pH = 2 and conversion of pepsinogen to pepsin.

4)G-cells: make and secrete GASTRIN into the BLOOD. It circulates back to the parietal and chief cells stimulating them to release HCl and pepsinogen thus further enhancing digestion. Gastrin is a peptide-hormone.


Recall from BIOLOGY 1

Acid in the stomach denatures proteins. Acid is a protein denaturing agent.


What prevents the tissues lining the stomach from being digested by pepsin?

The lining cells of the stomach are protected by a thick layer of mucus secreted by the mucus cells that line the gastric pits (one of four cells)



Regulates blood concentrations of many different solutes, plays key roles in the metabolism of proteins, fats, and carbohydrates, detoxifes chemicals, recycles metabolites, and manufactures several key biomolecules.


Some functions of the LIVER

- Produces BILE (stored and concentrated in GALL BLADDER)
- Filters the blood to remove toxins, drugs, metabolites, bacteria, etc.
- Produces blood plasma proteins, including ALBUMIN, PROTHROMBIN and FIBRINOGEN
- Regulates amino acid levels in the blood
- Produces cholesterol and lipoproteins and packages them for transport (LDL, HDL, etc)


Role of Liver in GLUCOSE metabolism

- In response to low-blood glucose levels, alpha cells in the pancreas secrete GLUCAGON, which stimulate glycogenolysis in the liver (the breakdown of glycogen stored in the liver to form free glucose for release into the blood.)
- High blood-glucose levels stimulate beta cells in the pancreas to secrete INSULIN, which stimulate glycogenesis in the liver (the synthesis of glycogen for storage in the liver).
Insulin also stimulates uptake of glucose from the blood into the cells.
- The liver also makes glucose out of lactate, glycerol, amino acids, and some TCA cycle intermediates.



- Exocrine (enzymes) and endocrine (insulin and glucagon) gland
- Secretes bicarbonate rich solution, neutralizing the stomach acid, decreasing the acidity of the intestine to pH = 6.
- All pancreatic secretions empty into the upper end of the duodenum. Just before emptying into the duodenum, the pancreatic duct is joined by the bile duct.


Functions of pancreatic enzymes

Trypsin & chymotrypsin: proteases. Each enzyme cuts proteins at its own specific amino acid sequence.
Pancreatic amylase: catalyzes hydrolysis of carbohydrates
Lipase: catalyzes hydrolysis of fats.
Ribonuclease and deoxyribonuclease: catalyzes hydrolysis of RNA and DNA respectively.



Stores and concentrates bile, but DOESN'T produce it.
- Bile emulsifies fats (separates fat molecules from each other, increasing the surface area available for enzymatic activity).
- Since bile doesn't break any bonds, it is an example of physical digestion.


Small Intestine

- Where the majority of digestion and absorption occurs
- Digestion mainly in the duodenum, absorption primarily in jejunum and ileum.


Important parts of the small intestine

- Villi: finger-like projections of the wall of the small intestine. They are hollow and contain both blood vessels and a single lymphatic vessel called a LACTEAL, where fats are absorbed into the lymph system, while carbohydrates and proteins are absorbed into the blood. They dramatically increase the surface area for absorption.
- Microvilli: each epithelial cell lining a villus contains fingerlike projections of the cell membrane called microvilli.
- Brush border- name given to microvilli and collection of mucus and digestive enzymes intermingled within them. Name chosen due to fuzzy appearance along apical surface of the epithelial cells (under light)


Large Intestine

Also absorbs vitamins produces by beneficial symbiotic E. Coli bacteria that live in the large intestine (VITAMIN K, THIAMIN, RIBOFLAVIN, and B12)
- This is MUTUALISM (bio 2), since both organisms benefit.


What could a disease or illness that inhibits normal function of the large intestine cause?

Vitamin deficiency or problems with water balance.
- Too little water absorption causes diarrhea, too much water absorption causes constipation.


Carbohydrate Digestion and Absorption

- Digestion begins in the MOUTH (SALIVARY AMYLASE), and is completed by the end of the small intestine.
- Broken down to their monomers before absorption.
- Enter the blood stream and travel to the liver via the hepatic portal vein


Protein Digestion and Absorption

- Protein digestion begins in the STOMACH, and it is complete by the end of the small intestine.
- They are broken down to small peptides and amino acids before absorption.
- Enter the blood stream and travel to the liver.


Lipid Digestion and Absportion

- Digestion begins in the small intestine (DUODENUM) and is complete by the end of the small intestine. Digestion of lipids CANNOT begin prior to their reaching the small intestine where they encounter BILE and LIPASE.
- Triglycerides are broken down to fatty acids, transported across the membrane, then reformed into triglycerides.
-Lipids ENTER THE LACTEALS (not the blood stream).
- In order to travel in blood or lymph, lipids must be 1) bound to protein carrier such as ALBUMIN, or 2) be formed into a chylomicron or micelle.


Immune System

Protect body from infection and disease; destroy pathogens invading body



- White blood cells, the mature form of a MONOCYTE
- Phagocytize (swallow) pathogens and cellular debris.
- Participate in INNATE INMUNITY
- Present antigens on MHC (major histocompatability complex) proteins from the pathogens they consume on their cell membrane which are recognized by B and T cells - a role in AQUIRED INMUNITY.



- One of three kind of granulocytes (basophils and eosinophils)
- Three cells get their names from how they appear when stained and viewed under light microscope. (Baso - blue, eosino - bright red)
- They are phagocytes that are recruited to areas of infection and inflammation by chemotaxis.
- They live for about 5 days, but are the most abundant of all white blood cells.
- PUS created at wound sites is mostly dead neutrophils



- Least common white blood cell
- Granules contain mostly HISTAMINE, which they release along with other chemicals when activated.
- These chemicals promote inflammation and are integral in the allergic response, so many think basophils as roughly associated with allergies.



- Recruited to areas of parasitic invasion, particularly multicellular parasites where they release their granules containing peroxidases and other enzymes that digest tissue.
- This destroy the pathogen but could also destroy host tissue.



- Term comes from the fact that three cells (neutrophils, basophils, eosinophils) contain large cellular granules easily visible with a microscope.
- All granulocytes are short-lived and do not reside permanently in the tissues
- They circulate in the blood and are recruited to areas of infection/inflammation


Mast Cells

- Contrary to granulocytes, are permanent resident cells within many tissues.
- They are activated by allergens and other antigens to release histamine and other chemical mediators.
-They are usually associated with severe allergic reactions, including anaphylactic shock


Dendritic Cells

- Professional antigen-presenting cells, found in high concentrations near membranes, like the skin, which is most likely to encounter antigens.
- Efficiently phagocytize pathogens and present those antigens on their surface to stimulate other immune cells.
- They are white blood cells (leukocytes), but are not lymphocytes
- They can form from monocytes (also differentiate into macrophages) or independently in their own cell line from a blood cell precursor.



T cells
B cells
Natural killer cells


Natural Killer cells

- Recognize infected or cancerous cells and release cytotoxic granules that destroy the cell


T Cells

-Lymphocytes that mature in the THYMUS and participate in cell-mediated immunity
- Recognize and bind antigens via a "T-CELL RECEPTOR" (TCR) not found on B-cells



Lymphocytes that mature in the BONE MARROW and lymph tissues and participate in HUMORAL IMMUNITY.
- Produce ANTIBODIES, T cells DO NOT.
- Present a portion of antigen on MHC proteins in their cell membrane. Helper T-cell recognize and bind this antigen, and stimulates B-cell to divide into a plasma cell and a memory-B cell.


Plasma cells

- Formed when B cell binds its matching antigen and is activated (with the help of helper T-cells) to undergo mitosis.
- This mitosis produces mostly plasma cells (clones of the original B-cell that act as "antibody factories", making and secreting soluble copies of that antibody)


Memory B Cells

- Few cells differentiate into them
- Allow the immune system to mount a more efficient secondary immune response if there is a later infection by the same pathogen.


Helper T Cells

- T cells that "help" other immune system cells, such as B-cells and cytotoxic T-cells to perform their function.
- Help by secreting chemicals, such as cytokines, that activate ("turn on") functions or activities in the cell that is being "helped"


Suppressor T-cells

AKA Regulatory T-cells
- Suppress the body's own immune system, which helps prevent severe allergic reactions or autoimmune disease, and aides in turning off an immune response once an infection has been eliminated.


Killer (or cytotoxic) T-cells

- Target infected and cancerous versions of the body's own cells and destroy them.


Memory T-cells

Analogues to memory B-cells that have previous experience with a pathogen that allows them to mount a more effective response during a subsequent infection.



- Concepts of immunological "memory" and a "secondary immune response" are so intricately associated with HUMORAL IMMUNITY that the wisest choice would be to always associate such concepts with B-cells and humoral immunity ONLY.


Innate Immunity

- Non-specific attack of pathogens that a person is born with
- Includes responses that are NOT specific to one particular virus, bacteria, pathogen, etc.
- Stomach acid, skin, enzymes in mucus and saliva, digestive enzymes, blood chemicals, fevers, inflammation, and non-specific phagocytosis


Inflammatory Response

1. Macrophages, mast cells, and dendritic cells are residents of nearly all tissues
2. When damage is caused by injury, bacterial invasion, etc, these cells are activated to release chemicals such as histamines, leukotrienes, and prostaglandins.
3. These chemicals increase blood flow to injury site, creating heat and redness. Also increase permeability of veins and lymph vessels.
4. This causes plasma and interstitial fluid to flood the infection site, resulting in swelling.
5. Neutrophils are recruited via chemotaxis in very large numbers to inflammation site.


Acquired Inmunity

Specific response to one particular virus, bacteria or other pathogen based upon prior exposure.


Humoral Immunity

- Involves B CELLS (B lymphocytes). When you see B cells or "antibody" think HUMORAL
- B cells produce ONLY ONE of the certain kind of protein receptor on its membrane called an ANTIBODY (aka immunoglobulin).
- Each antibody will recognize and bind with ONLY ONE foreign particle called an ANTIGEN.
- If an antigen binds to a B cell's antibody, the B-cell will undergo differentiation into a PLASMA CELL and a MEMORY B-CELL.
- PLASMA CELLS manufacture free antibodies and release them in the blood
- MEMORY B CELLS multiply and remain in the blood, preparing the body for secondary response.


Cell-Mediated Immunity

- T-cell Immunity. When you see T-cells, think cell-mediated.
- T-cells have receptor proteins in embedded in their cell membrane, and unlike B cells, they NEVER produce free antibodies.
- Instead, they are "tested" in the THYMUS against the host's own membrane proteins (called "self-antigens")
-ALL T-CELLS MATCHING A SELF-PROTEIN ARE DESTROYED, leaving only cells that will recognize invader antigens
- T-cells that pass this "test" will differentiate into one of the T-cell types described


Tissues of the Immune System
Bone Marrow

- All erythrocytes and leukocytes are made in the red bone marrow via hematopoiesis
- Yellow bone marrow is primarily adipose tissue and does NOT produce blood cells
- B lymphocytes mature in the bone marrow
- T-lymphocytes migrate to the thymus to mature



- Filters blood instead if lymph
- High concentration of leukocytes (WBCs) and platelets
- Storage of considerable amount of blood to help combat hemorrhagic shock
- Breaks down and recycles parts of old RBCs



Location where T lymphocytes acquire immunocompetencey, differentiate and mature


Lymph nodes

High concentrations of B and T lymphocytes.
Filters blood pathogens
Other lymphatic tissue similar to this is spread throughout body, common in digestive and respiratory systems


Antibody questions

Antibodies are never created "in response to" or to "match" antigens. Antibody creation is a random process. The sheer number of antibodies created, coupled with a somewhat flexible binding requirement, ensures that foreign antigen will be bound by a host antibody.


Integumentary System

Functions: protection against abrasion, physical barrier to pathogens, vitamin D synthesis, insulation/cushioning (subcutaneous fat), prevention of water-loss, temperature regulation



Epidermis: avascular, made up of mostly dead or dying, keratinized cells.
Dermis: contains blood vessels, hair follicles, sebaceous glands (oil), sudoriferous glands (sweat), and nerve endings. CONNECTIVE TISSUE


Thermoregulation of Skin

1) Blood vessels closer to the surface of the skin DILATE when heat needs to be released and CONSTRICT when heat needs to be retained. Blushing is the result of the dilation of these superficial blood vessels.
2) Arrector pili muscles cause erection of the hair follicles (resulting in goose bumps, that traps an insulating layer of air next to the skin. Contraction of the arrector pili muscles can also generate a small amount of heat.
3) Subcutaneous fat provides insulation
4) Sweating, followed by evaporation of that sweat, carries away significant amount of heat due to the high heat of vaporization of water and its high specific heat capacity.


Musculoskeletal System

Movement, support, stabilization, generation of heat, aide to circulation, and maintenance of homeostasis


Skeletal Muscle Anatomy

Muscle group is a bundle of FASICULI
Each fasicle is a bundle of many long, tubular cells called MUSCLE FIBERS
Each muscle cell is surrounded by a specialized membrane called SARCOLEMMA.
Inside each muscle cell are many nuclei.
Nearly entire volume of each cell is filled with smaller round tubes called MYOFIBRILS
Myofibrils are long bundles of proteins mainly composed of ACTIN and MYOSIN fibers interconnected in repeating units called SACROMERES.
Bundles of myofibrils are interwoven among portions of the muscle cell's ER, called the sacroplasmic reticulum, which stores and releases Ca2+ to control contraction.


The Sarcomere

- Thick filaments: made of myosin fibers
- Thin filaments consist of mostly actin fibers, also known as microfilaments (feature troponin and tropomyosin).
- Actin- protein, of which microfilaments are polymers
- Myosin- protein with both a head moiety and tail moiety. Dimer formed between two myosin. Head "bent" is in relaxed position. High affinity for actin.
- A band- length of the myosin filament (NO CHANGE in contraction)
- I Band- distance between the ends of the myosin filaments, lightest band when viewed under microscope because only the thin actin filaments are present (SHORTENS in contraction)
- H zone- distance between the ends of the actin filaments (in the middle), SHORTENS in contraction
- Z lines- zigzag lines that define the edges of each individual sarcomere unit, where actin filaments are anchored by protein connectin and stretch out in both directions. Distance DECREASES between them as sarcomere shortens.
- M line- very center of myosin filaments. Distance between M lines will decrease during contraction.


Sliding Filament Mechanism

Review steps


Motor Units

Group of muscle cells innervated by a single motor neuron. Come in all different sizes from large to small.
DELICATE MOVEMENTS = very small motor units
GROSS MOVEMENTS = large motor units
Strength of given contraction depends on the
1) Number of motor units being used
2) Size of the motor units being used
3) Frequency of action potentials


Cardiac Muscles

- Involuntary, striated, one nucleus
- Contraction same as skeletal
- It contains high numbers of mitochondria to prevent fatigue.
- Cardiac muscle fibers/cells are connected by intercalated discs containing GAP JUNCTIONS, which are used by ions to initiate action potentials.
- Cardiac cells continue dividing after differentiation
- Heart is autorhythmic. SA node starts action potential.


Smooth Muscle

- Involuntary, non-striated, one nucleus
- Controls gut, viscera, blood vessels, etc.
- NOT arranged in sarcomeres.
- DOES NOT contract as skeletal or cardiac muscle
- Actin and myosin involved, but several other proteins are involved.
- Contraction is initiated by the calcium-dependent phosphorylation of the myosin head.
- "Calcium-calmodulin cascade"


Single unit vs. multi unit smooth muscle types

Single unit: group of smooth muscle fibers that are innervated by a single nerve and contract simultaneously as a single group. Most common units, found in most organs, around most blood vessels, digestive track, etc.

Multi Unit: smooth muscle innervated by multiple nerves and does not act as a single unit. This ALLOWS FOR MORE PRECISE CONTROL (remember, however, that all smooth muscle is involuntary, so no CONSCIOUS control). Quite rare. Larger vessels like aorta, and retina of the eye.


Bone Cell Types

Osteocytes: mature bone cells surrounded by a mineral matrix

Osteoclasts: bone cells that break down and resorb bone matrix, releasing the component minerals, Ca2+ and P, back into the blood

Osteoblasts: immature bone cells that secrete collagen, organic compunds, and minerals forming bone matrix around themselves. Once completely enclosed in matrix, differentiate into osteocytes.


Hormonal Regulation of Bone cells.

CALCITONIN: "calcitonin tones your bones". When blood levels are above normal calcitonin inhibits OSTEOCLAST activity. OSTEOBLAST activity continues and thereby a net increase in bone structure results. Calcium used by osteoclasts to build new bone matrix comes from the blood and therefore CALCIUM LEVELS DECREASE.

PARATHYROID HORMONE (PTH): opposite effect. It stimulates OSTEOCLAST activity, resulting in breakdown of bone matrix, and release of the associated calcium INTO the blood. As a result, blood calcium levels RISE. These hormones also have predictable impacts on the absorption of calcium at the gut and the reabsorption of calcium in the kindey.



Name given to the formation and differentiation of blood cells in the bone marrow. Occurs in RED BONE MARROW that fills pockets of SPONGY BONE. It DOES NOT occur in YELLOW BONE MARROW (mostly fat) that fills the medullary cavity of long bones.

COMPACT BONE is the dense bone that surrounds the outside of all bones, and makes the shafts of long bones. Interior of flat and irregular bones, as well as bulbous ends of long bones is filled with SPONGY BONE, which contains open spaces, filled with RED BONE MARROW. COMPACT BONE is organized into orderly units called osteons, and the only spaces it contains are Haversion canals and canaliculi.



Inorganic compound of calcium, phospate, and hydroxide. It is the mineral matrix responsible for a bone's strength and is the form in which most all of the body's calcium is stored.


Secretion of the Male reproductive glands

Seminal vesicles: release majority of the fluids that make up semen, including FRUCTOSE and ALKALINE FLUIDS that make the semen basic. The basic nature of semen helps neutralize acidic environment in vagina, and fructose provides nutrients for sperm.

Prostate gland: secretes milky white fluid that is slightly acidic and contains proteases. They play a protective role, as sperm have been shown to have longer survival rates and better protection of their genetic material in the presence of prostate secretions as compared to w/o them.

Bulbourethral gland: do NOT add fluids to the ejaculate at this point. They secrete a fluid called PRE-EJACULATE that lubricates and neutralizes any acidic urine in the urethra prior to the arrival of the other semen components.


Embryology Definitions

Cleavage: mitosis without change in size

Morula: 8-cell zygote

Gastrulation = at about week 2 cells migrate to form the three germ layers

Neurulation = at about week 3, the NOTOCHORD forms from the mesoderm and induces overlying ectoderm to form the NEURAL PLATE, which becomes the NEURAL TUBE, which becomes the SPINAL CHORD.


3 Germ Layers

Ectoderm: epidermis, nails, tooth enamel, lens of the eye, pituitary gland, central, peripheral and autonomic nervous systems

Mesoderm: dermis muscle, bone, connective tissues, kidneys, genitalia and most internal organs EXCEPT the liver and pancreas.

Endoderm: entire digestive tract, thyroid, parathyroid, urinary bladder, the lining ONLY of the lungs, and the liver and pancreas.


A woman suffering from a heritable hormone abnormality has above normal levels of estrogen and progesterone in her blood, but little to no LH or FSH. Based on this information, one would expect this woman to:

a) develop thick uterine lining and have heavy menstrual flow
b) develop thick uterine lining but lack regular menses
c) be at risk for multiple births
d) exhibit an over-developed corpus luteum

B. MCAT directly associates high estrogen/progesterone levels with thickening of of the uterine lining.