Biology Flashcards
(246 cards)
1
Q
Hyperventilation
A
An increase in the rate of respiration or tidal volume. Lack of oxygen or a decrease in blood pH promotes hyperventilation.
2
Q
Pathway of the Respiratory Tract
A
Air travels through the nasal or oral cavity, pharynx, larynx, trachea, bronchi, bronchioles, and finally the alveoli (site of gas exchange).
3
Q
Pathway of the Electrical Impulse in the Heart
A
The electrical impulse originates in the sinoatrial (SA) node, located in the right atrium. It then travels through the atrioventricular (AV) node, then through the bundle of His, and finally through the Purkinje fibers.
4
Q
Cell Theory
A
A foundational belief in modern biology that all living things are composed of cells, the cell is the basic functional unit of life, that all cells arise from preexisting cells, and that DNA is the genetic material.
5
Q
Gene
A
A unit of DNA that encodes a specific protein or RNA molecule.
6
Q
Mitochondria
A
The sire of aerobic respiration that provides the cell with a majority of its energy in the form of ATP. A mitochondrion is a semiautonomous organelle enclosed by two membranes with an intermembrane space between the two membranes and a mitochondrial matrix enclosed by the inner membrane.
7
Q
Lysosome
A
A membrane-bound vesicle that contains hydrolytic enzymes used for intracellular digestion.
8
Q
Golgi Apparatus
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An organelle that plays a role in the packaging and secretion of proteins and other molecules produced intracellularly.
9
Q
Centrosome
A
The portion of the cell containing the centrioles
10
Q
Facultative Anaerobe
A
An organism that makes ATP by aerobic respiration if oxygen is present, but that can switch to fermentation for sufficient ATP when oxygen is not available.
11
Q
Conjugation
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The temporary joining of two organisms via a tube called a pilus, through which genetic material is exchanged; a form of sexual reproduction used by bacteria.
12
Q
Recombination Frequency
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The likelihood of two genes on the same chromosome being separated onto two different chromosomes during crossing over; equal to the proportion of gametes that receive these recombinant chromosomes. If the recombination frequency of two particular traits is high, it can be inferred that they lie far apart from each other.
13
Q
Ribonucleic Acid (RNA)
A
A nucleic acid found in both the nucleus and cytoplasm and most closely linked with transcription and translation, as well as some gene regulation.
14
Q
Reverse Transcriptase
A
An enzyme in retroviruses that uses RNA strands as templates for synthesizing cDNA molecules.
15
Q
Diploid
A
Cells with two copies of each chromosome, usually one from the mother and one from the father. Eukaryotic somatic cells are diploid.
16
Q
Haploid
A
Cells with only one copy of each chromosome. Germ cells in humans are haploid.
17
Q
Interphase
A
Phase of the cell cycle in which cell division does not take place. Includes the G1 phase, S phase, and G2 phase. Cells in this phase may or may not be growing.
18
Q
Chromatin
A
Chromosomes in their uncoiled state. Chromatin itself is not visible as organized chromosomes under a light microscope.
19
Q
Mitosis
A
Cell division or nuclear division in somatic cells that results in the daughter nucleus receiving a full complement of the organisms genome.
20
Q
Somatic Cells
A
All cells excluding the germ (reproductive) cells.
21
Q
Meiosis
A
A two-phase cell division in germ cells that results in the formation of up to four haploid cells from one diploid cell.
22
Q
Homologous Chromosomes
A
Chromosomes in a diploid cell that contain alleles for the same traits at corresponding loci.
23
Q
Tetrad
A
Collectively, the four chromatids involved when a pair of homologous chromosomes synapse during prophase I of meiosis.
24
Q
Crossing Over
A
The exchange of genetic material between homologous chromosomes that occurs during prophase I of meiosis. Crossing over aids in evolutions and genetic diversity by unlinking linked genes.
25
Mendel's Law of Independent Assortment
The alleles of different genes sort independently from one another during meiosis. We now know that this is true only for unlinked genes.
26
Nondisjunction
The failure of homologous chromosomes or sister chromatids to separate properly during meiosis I or meiosis II, respectively. This usually results in gametes that lack certain genes or have multiple copies of those genes.
27
Testosterone
Hormone secreted by the interstitial cells of the testes. Testosterone is responsible for embryonic sexual differentiation, male sexual development, and the maintenance of masculine secondary sexual characteristics.
28
Spermatozoa
Mature sperm specialized for transporting the genetic information from the male to the ovum.
29
Acrosome
The large vesicle at the head of a sperm cell containing enzymes that degrade the ovum cell membrane to allow fertilization.
30
Corona Radiata
Outer layer of cells surrounding the oocyte. These cells are derived from follicular cells.
31
Polar Body
A small, short-lived haploid cell created during oogenesis that receives very little cytoplasm, organelles, or nutrients.
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Zygote
A fertilized egg. Develops into a morula after a number of rounds of cleavage.
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Anterior Pituitary
Synthesizes and releases many vital hormones, including follicle-stimulating hormone, luteinizing hormone, adrenocorticotropic hormone, thyroid-stimulating hormone, prolactin, endorphins, and growth hormone ("FLAT PEG"). The anterior pituitary is under the hormonal control of the hypothalamus.
34
Follicle-Stimulating Hormone (FSH)
Synthesized and released by the anterior pituitary , FSH stimulates maturation of ovarian follicles in females and maturation of the seminiferous tubules, and sperm production in males. FSH is regulated by estrogen and gonadotropin releasing hormone (GnRH).
35
Estrogen
Hormone synthesized and released by the ovaries, ovarian follicles, corpus luteum, and placenta. Estrogen stimulates the development of the female reproductive tract and secondary sexual characteristics and is partly responsible for the LH spike that causes ovulation.
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Endometrium
The mucosal lining of the uterus where the embryo implants. Progesterone is necessary for the maintenance of the endometrium during pregnancy
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Progesterone
Hormone synthesized and released by the ovaries, corpus luteum, and placenta. During the luteal phase of the menstrual cycle, the corpus luteum secretes progesterone, which, along with estrogen, stimulates the development and maintenance of the endometrial walls for implantation of the embryo.
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Corpus Luteum
Tissue that forms from the collapsed ovarian follicle. Produces and secretes progesterone and estrogen.
39
Dizygotic Twins
Results when two ova are fertilized by two different sperm. Because the two resulting embryos develop from distinct zygotes, they do not have identical alleles. Also referred to as fraternal twins. Contrast with monozygotic twins.
40
Monozygotic Twins
Result when a zygote splits into two embryos. Because both embryos contain identical alleles, they are often called identical twins. Contrast with dizygotic (fraternal) twins.
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Determinate Cleavage
Division of cells during embryogenesis in which each cell specializes early in development. By extension, each cell is not necessarily able to differentiate into an entire organism on its own.
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Indeterminate Cleavage
Cell division in embryogenesis that results in each cell maintaining its totipotency, or ability to develop into a complete organism by itself.
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Morula
A solid ball of cells that develops from the zygote through cleavage. When the interior of the morula becomes hollow, it becomes known as a blastula.
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Blastulation
The process by which a morula develops into a blastula with a fluid-filled cavity called a blastocoel.
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Umbilical Cord
Connects the vasculature of the fetus to the placenta
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Amnion
The innermost extraembryonic membrane; produces the amniotic fluid in which the growing fetus is suspended.
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Placenta
The organ formed by the uterus and the extraembryonic membranes of the fetus. The placenta contains a network of capillaries through which exchange between the fetal circulation and maternal circulation takes place.
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Gastrulation
The process by which a single-layered blastula becomes a three-layered gastrula.
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Ectoderm
The outermost of the three primary germ layers; gives rise to the skin, nervous system, lens of the eye, and inner ear.
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Mesoderm
Primary germ layer that lies between the ectoderm and the endoderm. Gives rise to the musculoskeletal system, circulatory system, excretory system, gonads, connective tissue throughout the body, and portions of the digestive and respiratory organs.
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Endoderm
The innermost of the three primary germ layers; gives rise to the linings of the digestive and respiratory tracts and to parts of the liver, pancreas, thyroid, and bladder
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Totipotent
Stem cells that have the ability to become any cell within any system of the body. Embryonic stem cells are totipotent.
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Pluripotent
Stem cells that can become other cells within the same primary germ layer. For example, after gastrulation, cells of the endodermal layer can only become derivates of endoderm.
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Multipotent
Stem cells that can differentiate into multiple cell types within a particular group. For example, hematopoietic stem cells are able to differentiate into many different types of blood cells, but not into any other cell type.
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Action Potential
A sharp change in the membrane potential of neurons or muscle cells caused by a change in the selective permeability to Na+ and K+ using voltage-gated ion channels. Action potentials are all-or-nothing events.
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Axon Hillock
The portion of the neuron that connects the cell body (soma) to the axon. The impulses the neuron receives from all the dendrites are summed up at the axon hillock to determine whether or not an action potential will be initiated.
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Dendrite
An extension of the neuron that transmits impulses toward the cell body.
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Myelin Sheath
Insulating structure that surrounds axons. Action potentials cannot take place in areas of the axon that are myelinated.
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Schwaan Cells
Cells that produce myelin int he peripheral nervous system
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Nodes of Ranvier
Gaps between segments of myelin sheath where action potentials can take place, allowing for saltatory conduction.
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Neurotransmitters
Chemical messengers released from synaptic terminals of a neuron that can bind to and stimulate postsynaptic cell.
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Synaptic Terminals
End of axons that form one side of the synaptic cleft; the location where vesicles of neurotransmitters are stored.
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Synapse
The space between the axon terminal of one neuron and the dendrite of another neuron (or membrane of an effector organ) where neurotransmitters are released.
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Resting Potential
The charge difference across the cell membrane of a neuron or a muscle cell while at rest. Most often maintained by the sodium-potassium pump.
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Sodium-Potassium Pump
A protein that hydrolyzes one ATP to transport three Na+ out of the cell for every two K+ it transports into the cell.
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Depolarization
A process that occurs when the voltage-gated Na+ channels open, allowing Na+ to rush into the cell and depolarize it.
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Threshold Voltage
The minimal voltage that must be reached in order for an action potential to be fired at the axon hillock.
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Repolarization
A process that occurs when the voltage-gated Na+ channels close and voltage-gated K+ channels open during an action potential, allowing K+ to rush out of the cell and repolarize it
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Refractory Period
A short period of time immediately following an action potential in which neurons or muscle cells are unresponsive to a stimulus (absolute refractory period). In some cases, a stimulus that is much larger than usual causes an action potential in a cell in a refractory period (relative refractory period).
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Saltatory Conduction
A means by which action potentials jump from node to node along an axon.
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Afferent Neurons
Neurons that carry information to the central nervous system from the periphery. Also called sensory neurons.
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Efferent Neurons
Neurons that carry information from the central nervous system to other parts of the body. Also called motor neurons.
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Central Nervous System
The central nervous system consists of the brain and the spinal cord.
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Ganglia
A group of neuronal cell bodies int he peripheral nervous system. May be sensory or autonomic.
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Peripheral Nervous System
All neurons that are not part of the central nervous system, including sensory and motor neurons that connect to the central nervous system. Can be divided into the somatic nervous system and the autonomic nervous system.
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Somatic Nervous System
Division of the peripheral nervous system that is responsible for voluntary movement.
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Monosynaptic Reflex
Reflex pathway that has only one synapse between the sensory neuron and the motor neuron (such as the knee-jerk reflex).
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Peptide Hormones
Polar hormones incapable of permeating the cell membrane that bind to surface receptors and act through secondary messengers.
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Steroid Hormones
Nonpolar hormones that cross the cell membrane and act by binding intracellular receptors.
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Amino Acid-Derivative Hormones
Hormones that are synthesized by modifying amino acids. Most amino acid-derivative hormones act via secondary messengers, while some act in a fashion similar to steroid hormones.
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Second Messenger
A small molecule that transduces a hormonal signal from the exterior of the cell to the interior. Usually released when a peptide hormone binds to its receptor; cAMP is a common example.
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Signaling Cascade
Series of events, starting with the binding of a peptide hormone to a surface receptor. This sequence of events ultimately results in a change in cellular behavior.
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Catecholamines
Norepinephrine, epinephrine, and dopamine- neurotransmitters; also, hormones produced by the adrenal medulla that play a significant role in the sympathetic nervous system.
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Direct Hormones
Hormones that travel to a target tissue to cause an action without another hormone acting as an intermediary
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Tropic Hormones
Hormones that travel to a target tissue and cause the release of another hormone. A hormone downstream will cause the physiological effect.
86
Thyroid-Stimulating Hormone (TSH)
Synthesized and released by the anterior pituitary, TSH stimulates the thyroid gland to absorb iodine and to synthesize and secrete thyroid hormones. TSH is regulated by thyroid releasing hormone (TRH), which is released by the hypothalamus.
87
Adrenocorticotropic Hormone (ACTH)
Synthesized and released by the anterior pituitary, ACTH stimulates the adrenal cortex to synthesize and secrete glucorticoids. ACTH is regulated corticotropin releasing factor (CRF), which is released by the hypothalamus.
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Prolactin
Hormone synthesized and released by the anterior pituitary that stimulates milk production and secretion in female mammary glands.
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Posterior Pituitary
Stores and releases hormones (oxytocin and ADH) synthesized by the hypothalamus. The release of these hormones is triggered by an action potential that originates int he hypothalamus.
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Antidiuretic Hormone (ADH)
A peptide hormone, also known as vasopressin, that acts on the collecting duct to increase water reabsorption. ADH is produced by the hypothalamus and stored in the posterior pituitary.
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Growth Hormone (GH)
Synthesized and released by the anterior pituitary, GH stimulates bone and muscle growth as well as glucose conservation. GH is inhibited by somatostatin and stimulated by growth hormone releasing hormone (secreted by the hypothalamus).
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Parathyroid Hormone (PTH)
Synthesized and released by the parathyroid gland, PTH increases blood Ca2+ concentration by increasing Ca2+ reabsorption in the kidneys and by stimulating calcium release from bone.
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Glucocorticoids
Synthesized and released by the adrenal cortex, glucocorticoids raise blood glucose levels while decreasing protein synthesis.
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Pancreas
Its exocrine functions include secreting pancreatic amylase, trypsinogen, chymotrypsonogen, procarboxypeptidases A and B, and pancreatic lipase into the small intestine. Its endocrine functions include secretion of insulin and glucagon.
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Glucagon
Produced and secreted by the a-cells of the pancreas, glucagon increases blood glucose concentration by promoting gluconeogenesis and the conversion of glycogen to glucose in the liver.
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Insulin
Produced and secreted by the B-cells of the pancreas, insulin decreases blood glucose concentrations by facilitating the uptake of glucose by muscle and adipose cells and the conversion of glucose to glycogen in muscle and liver cells.
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Endocrine Glands
Glands that synthesize and secrete hormones into the circulatory system. Examples include the hypothalamus, pituitary gland, pineal gland, pancreas, testes, ovaries, adrenal glands, thyroid gland, and parathyroid glands.
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Exocrine Glands
Glands that synthesize and secrete substances through ducts. The mammary glands and sweat glands are examples of exocrine glands.
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Epiglottis
A flap of cartilage that covers the glottis when swallowing food in order to prevent food particles from entering the larynx.
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Intrapleural Space
The space between the two membranes (visceral pleura and parietal pleura) that cover the lungs.
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Respiratory Rate
Expressed as breaths per minute. Raising the respiratory rate can decrease the amount of carbon dioxide in the blood, thus increasing the pH. Likewise, decreasing the respiratory rate increases the concentration of carbon dioxide in the blood, resulting in a lower pH.
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Thermoregulation
Maintenance of a constant internal body temperature.
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Blood Buffer System
Relies primarily on the carbonic acid buffer system, demonstrated by the equation:
CO2 + H2O <=> H2CO3 <=> H+ + HCO3-
Release of carbon dioxide causes increased formation of water and an increase in pH.
Increased retention of HCO3- causes the pH to rise as well.
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Atria
The two thin-walled upper chambers of the heart. The right atrium receives deoxygenated blood from the venae cavae, while the left atrium receives oxygenated blood from the pulmonary veins.
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Ventricles
The muscular lower chambers of the heart. The right ventricle pump deoxygenated blood to the lungs through the pulmonary arteries, while the left ventricle pumps oxygenated blood throughout the body through the aorta. s deoxygenated blood to the lungs through the pulmonary arteries, while the left
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Arteries
Vessels that carry blood away from the heart. These vessels are muscular and do not have valves.
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Veins
Vessels that carry blood toward the heart. These vessels are thin-walled and have valves to prevent backflow.
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Atrioventricular Valves
Valves located between the atria and the ventricles (Tricuspid valve and mitral valve).
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Semilunar Valves
Valves (the aortic valve and the pulmonic valve) that prevent backflow of blood from the arteries into the ventricles.
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Tricuspid Valve
A valve located between the right atria and the right ventricle. The valve consists of three cusps and prevents backflow of blood from the right ventricle to the right atrium.
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Mitral Valve
A valve located between the left atrium and the left ventricle. The valve consists of two cusps and prevents backflow of blood from the left ventricle to the left atrium.
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Systole
The stage of the cardiac cycle in which the heart muscle contracts and pumps blood.
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Vagus Nerve
One of the twelve cranial nerves; the vagus nerve provides parasympathetic signaling to the thoracic and abdominal cavities.
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Diastole
The stage of the cardiac cycle in which the heart muscle relaxes and collects blood into its chambers.
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Capillaries
Blood vessels composed of a single layer of endothelial cells, facilitating exchange of gases, nutrients, and waste products between the blood and interstitial fluid
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Endothelial Cells
Cells that line blood vessels. These cells are able to produce and release chemicals that aid in vasodilation and vasoconstriction. In addition, damage to these cells results in the release of mediators that aid in clotting.
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Superior Vena Cava
A large vein that returns deoxygenated blood from the head and neck regions, as well as the upper extremities, to the right atrium of the heart.
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Inferior Vena Cava
A large vein that returns deoxygenated blood from the lower body and the lower extremities to the right atrium of the heart.
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Portal Systems
Circulatory routes in which blood travels through two capillary beds before returning to the heart. Some examples include the hypophyseal portal system, the hepatic portal system, and the renal portal system
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Hepatic Portal Vein
Carries nutrients (monosaccharides, amino acids, and small fatty acids) absorbed in the small intestine to the liver, where they are modified to enter circulation.
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Plasma
Liquid portion of blood, an aqueous mixture of nutrients, salts, respiratory gases, hormones, and blood proteins.
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Erythrocytes
The oxygen-carrying component of blood. These anaerobic cells, which lack organelles, are packed with hemoglobin and have a characteristic biconcave, disk-like shape that facilitates gas exchange and mobility within blood vessels. Also called red blood cells.
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Leukocytes
White blood cells; the component of blood involved in cell defense and immunity. Neutrophils, basophils, eosinophils, lymphocytes, and monocytes are types of leukocytes.
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Platelets
Cell fragments involved in the clotting process. Come from megakaryocytes in the bone marrow.
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Hemoglobin
A protein found in erythrocytes made up of four polypeptide chains, each containing a heme group. Hemoglobin is responsible for transporting oxygen from the alveoli to the tissues.
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Osteoclasts
Cells in the bone matrix that are involved in bone degradation.
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Osteoblasts
Cells in the bone tissue that secrete the organic constituents of the bone matrix. Osteoblasts develop into osteocytes.
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Antigen
A substance that is bound by an antibody, causing an immune reaction.
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Rh Factor
Nonspecific immunity provided by structures and cells. Structures, such as the skin, and cells, such as macrophages, are able to recognize invaders and kill them. Some cells of the innate immune system, such as macrophages and dendritic cells, are able to signal the presence of an invader to the adaptive immune system. Contrast with adaptive immunity.
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Adaptive Immunity
A highly specific form of immunity that develops in response to exposure to pathogens; consists of both humoral immunity and cytotoxic immunity. Contrast with innate immunity.
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Humoral Immunity
The synthesis of specific antibodies by activated B-cells in response to an antigen. These antibodies bind to the antigen and either clump together to become insoluble, neutralize the antigen, or attract other cells that engulf and digest the pathogen.
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Cell-Mediated (Cytotoxic) Immunity
Branch of the immune system in which intracellular pathogens are eliminated by killing their host cells. T-cells are the primary mediators of cytotoxic immunity.
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Lymph Nodes
Swellings along the lymph vessels where lymph is filtered by leukocytes to remove antigens.
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Immunoglobin
Synonymous with antibody; produced in response to a specific foreign substance that recognizes and binds to that antigen and triggers an immune response.
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Lymphatic System
A system of vessels and lymph nodes that collect interstitial fluids and return them to the circulatory system, thereby maintaining fluid balance. The lymphatic system is also involved in lipid absorption and lymphocyte activation.
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Mechanical Digestion
Breakdown of food particles into smaller particles through such activities as biting, chewing, and churning.
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Chemical Digestion
Enzymatic breakdown of large molecules into smaller molecules.
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Large Intestine
Section of the GI tract that consists of the cecum, the colon, and the rectum. The main function of the large intestine is to absorb salts, water, and some vitamins.
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Peristalsis
Involuntary muscular contractions that push food down the digestive tract.
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Pyloric Glands
Glands located in the walls of the stomach that secrete the hormone gastrin to increase gastric acid production.
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Chyme
Combination of partially digested food and acid that forms in the stomach.
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Pyloric Sphincter
A valve between the stomach and the small intestine that regulates the flow of chyme into the duodenum.
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Villi
Fingerlike projections that extend out of the small intestine in order to increase surface area for maximal absorption.
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Primary Response
The initial response to a specific antigen. During a primary response, T- and B-cells are activated and specific antibodies and memory cells for the antigen are produced.
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Secondary Response
Subsequent infections by pathogens that trigger a more immediate response from the memory cells produced during the primary immune response.
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Glomerulus
Network of capillaries within Bowman's capsule that serves as the site of filtration. Blood cells and proteins are too large to be filtered, but ions, glucose, and amino acids readily pass into the filtrate.
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Filtrate
The material that passes from the blood vessels into Bowman's space.
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Nephron
The functional unit of the kidney. Can be subdivided into Bowman's capsule, proximal convulated tubule, descending limb of the loop of Henle, ascending limb of the loop of Henle, distal convoluted tubule, and collecting duct.
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Osmoregulation
Maintenance of water and solute concentrations.
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Hypodermis
Layer of loos connective tissue below dermis that binds the dermis to the body.
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Dermis
The layer of skin beneath the epidermis that is subdivided into the papillary layer and the reticular layer. It contains the sweat glands, sense organs, blood vessels, and the bulbs of hair follicles; it is derived from the mesoderm.
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Epidermis
The outermost layer of skin, which is composed of the following sublayers: stratum basalis, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum. Serves as a protective barrier against microbial attack. Derived from the ectoderm.
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Skeletal Muscle
Type of muscle responsible for voluntary movement, consisting of multi nucleated, striated (striped) muscle fibers.
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Smooth Muscle
Nonstriated muscle, responsible for involuntary action. Controlled by the autonomic nervous system.
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Cardiac Muscle
Type of muscle found within the heart; may contain one or two nuclei. Involuntary, like smooth muscle, but appears striated, like skeletal muscle. Able to depolarize independent of the nervous system.
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Sarcoplasmic Reticulum
A modified form of endoplasmic reticulum; stores calcium that is used to trigger contraction when muscle is stimulated.
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Appendicular Skeleton
The bones of the pelvis, the pectoral girdles, and the limbs.
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Axial Skeleton
The skull, vertebral column, ribcage, and hyoid bone.
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Compact Bone
Much more dense than spongy bone, compact bone consists of Haversian systems (osteons).
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Spongy Bone
Lighter and less dense than compact bone, it consists of an interconnecting lattice of bony spicules (trabeculae). The cavities between the spicules contain bone marrow.
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Diaphysis
Cylindrical shaft of a long bone. Filled with bone marrow for the production of blood cells.
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Epiphysis
Dilated ends of long bones in the appendicular skeleton.
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Epiphyseal Plate
Portion of the bone where growth occurs; located in the epiphysis.
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Osteons
The structural unit of compact bone that consists of a central canal (either a Haversian or Volkmann's canal) surrounded by a number of concentric rings of bony matrix called lamellae.
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Cartilage
A firm, elastic, translucent connective tissue consisting of collagenous fibers embedded in chondrin. Produced by cells called chondrocytes. Cartilage is the principal component of embryonic skeletons and can harden and calcify into bone (ossify).
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Alleles
Genes coding for alternative forms of a given trait.
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Genotype
The genetic makeup of an individual
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Point Mutation
Mutation in which one nucleotide base is substituted by another. The protein products may or may not be functional.
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Inversion
A form of chromosomal rearrangement in which a portion of a chromosome breaks off and rejoins the same chromosome in the reverse position.
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Phenotype
The physical manifestation of an individual's genotype.
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Dominant
Describes an allele that requires only one copy to be expressed
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Recessive
Describes an allele that requires two copies to be expressed
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Homozygous
Organisms that contain two identical alleles of the same gene on homologous chromosomes.
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Heterozygous
Organisms that contain two different alleles for the same gene on homologous chromosomes.
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Incomplete Dominance
Describes a situation in which an organism heterozygous for a trait will have a phenotype that is intermediate between both homozygous phenotypes. Neither allele, therefore, is dominant or recessive. Contrast with codominance.
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Codominance
Describes a situation in which an organism heterozygous for a trait will have a phenotype that expresses both alleles in full. Both alleles, therefore, are dominant. Contrast with incomplete dominance.
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Expressivity
Refers to the variability in phenotypes (especially severity of a disease) that can occur with a given genotype.
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Sister Chromatids
The relationship between the stands of DNA after replication. Each chromosome consists of two identical chromatids held together at a central region called the centromere. After the mitotic spindle pulls the sister chromatids apart, each chromatid is referred to as a chromosome on its own.
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Frameshift Mutation
Mutation in which a number of nucleotides (except multiples of three) are either deleted or inserted. Such mutations lead to a shift in the DNA reading frame and often result in the translation of nonfunctional proteins.
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Genetic Drift
Changes in the composition of the gene pool by chance; often more produced in small populations.
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Translocation
A form of chromosomal rearrangement in which a portion of one chromosome swaps with a portion of a nonhomologous chromosome.
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Monohybrid Cross
A cross between two organisms where only one trait is being studied.
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Test Cross
A cross between an organism of an undetermined genotype and another that is homozygous recessive for the trait of interest.
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Genetic Map
Created by analyzing recombination frequencies of linked genes; a schematic that shows the distance between two genes or the order of several genes on a chromosome.
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Stabilizing Selection
Type of natural selection where the average phenotype is favored while those outside the norm are eliminated.
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Direction Selection
Type of natural selection where one extreme phenotype is favored over the average phenotype and other extreme phenotypes.
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Mode
The most frequently occurring value in a set of observations.
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Mean
The average, calculated as the sum of observed values divided by the number of observed values.
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Median
The simplest division of a set of values; the middle value that divides the values into the upper half and lower half.
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Mendel's Law of Segregation
Mendel's postulation that there are alternate versions of genes that account for genetic variation. Each individual has two alleles for each gene, with one maternal and one paternal in origin. During meiosis, these two alleles separate into two gametes each.
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Neural Crest Cells
Cells at the tip of the neural fold; this group of cells gives rise to many components of the peripheral nervous system and a number of other cell types throughout the body.
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Inner Cell Mass
The group of cells in a blastocyst (mammalian blastula) that develop into the embryo.
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Pepsin
Secreted as pepsinogen by the chief cells of the stomach, this enzyme cleaves peptide bonds, starting the digestion of proteins into individual amino acids.
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Carbonic Anhydrase
Enzyme that catalyzes the conversion of carbonic acid to carbon dioxide and water as well as the formation of carbonic acid from carbon dioxide and water. Important in the bicarbonate buffer system.
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Collecting Duct
Portion of the nephron permeable to water and ions. As the filtrate flows down the collecting duct through the increasing concentration of the interstitium, the filtrate is concentrated. The degree of water reabsorption in the collecting duct is controlled by the action of the hormone ADH.
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Peroxisome
Organelle that contains hydrogen peroxide and participates in the breakdown of very long chain fatty acids.
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Binary Fission
Method of asexual reproduction by which prokaryotes divide. The circular DNA molecule replicates and then moves to the edge of the cell. The cell then divides into two daughter cells of equal size.
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Semen
The fluid discharged during ejaculation. Semen consists of sperm cells and seminal fluid (fluid from the prostate and bulbourethral glands).
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Primary Spermocytes
Diploid cells that undergo meiosis I to form two haploid secondary spermatocytes.
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Follicle
A multilayered sac of cells that protects and nourishes that developing ovum.
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Zona Pellucida
Inner layer of glycoproteins surrounding the oocyte. These glycoproteins are secreted by follicular cells and the oocyte itself. Penetration of the zona pellucida by a sperm cell forces the secondary oocyte to undergo meiosis II.
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Luteinizing Hormone (LH)
Synthesized and released by the anterior pituitary. LH simulates ovulation and the formation of the corpus luteum. LH is regulated by estrogen, progesterone, and gonadotropin releasing hormone (GnRH).
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Allantois
The embryonic membrane that contains the growing embryo's waste products.
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Calcitonin
Hormone synthesized and released by the thyroid gland that decreases plasma Ca2+ concentration.
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Adrenal Cortex
Synthesizes and releases corticosteroids. Glucocorticoids are stimulated by adrenocorticotropic hormone (ACTH), whereas mineralcorticoids are stimulated by angiotensin II. Cortical sex hormones include androgens such as testosterone.
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Negative Pressure Breathing
The contraction of the diaphragm and the intercostal muscles increases the volume of the thoracic cavity, reducing the pressure in the intrapleural space. This decrease in pressure creates a vacuum that causes the lungs to suck in air.
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Small Intestine
Section of the digestive tract that can be subdivided into three sections: duodenum, jejunum, and ileum. Most digestion takes place in the duodenum and most absorption takes place in the jejunum and the ileum.
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Descending Limb of the Loop of Henle
Portion of the nephron permeable only to water. The filtrate becomes more concentrated (loses water) as it travels through the descending limb due to the increasing concentration of the intersitium.
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Ascending Limb of the loop of Henle
Portion of the nephron not permeable to water. As the filtrate flows up the ascending limb through a decreasing concentration to the interstitium NaCl is first passively then actively removed from the filtrate, decreasing filtrate concentration.
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Sacromere
The structural unit of striated muscle. It is composed of thin (mostly actin) and thick myosin filaments.
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Transverse Tubules (T-Tubules)
A system of tubules that provides channels for ion flow throughout skeletal and cardiac muscle fibers to facilitate the propagation of an action potential.
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Obligate Intracellular Organisms
Organisms that require a host cell to express their genes and reproduce.
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Bacteriophages
Viruses that can only infect bacteria.
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Disjunction
The separation of homologous chromosomes during anaphase I of meiosis.
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Seminiferous Tubules
Located in the testes, the seminiferous tubules are the site of sperm production.
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Chorion
The outermost extraembryonic membrane; contributes to the formation of the placenta.
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Induction
The influence of a group of cells on the development of other cells. Induction is achieved by chemical substances known as inducers. The cells secreting these inducers are sometimes called organizers.
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Foramen Ovale
A shunt that connects the right atrium to the left atrium in order to bypass the fetal lung.
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Ductus Venosus
A shunt that connects the umbilical vein to the inferior vena cava in order to bypass the fetal liver
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Endorphins
Synthesized and released by the anterior pituitary, endorphins inhibit the perception of pain.
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Somatostatin
Produced and secreted by the d-cells of the pancreas, somatostatin inhibits the release of glucagon and insulin.
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Surfactant
A liquid substance produced by the lung that reduces surface tension in the alveoli. Surfactant prevents lung collapse and decreases the effort needed to expand the lungs (inhale).
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Starling Forces
A balance between hydrostatic and oncotic pressures on both sides of a membrane, essential for maintaining proper fluid volumes and solute concentrations inside and outside the vasculature.
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Liver
Essential organ of the human body responsible for the production of bile, detoxification of ingested substances, production of urea, and the processing and modification of nutrients for storage. The liver also produces albumin (a protein that maintains blood oncotic pressure) and clotting factors.
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Enteric Nervous System
A collection of millions of neurons within the gastrointestinal system that governs the function of the GI tract. This system is able to function independently of the brain and spinal cord.
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Intrinsic Factor
A protein secreted by parietal cells of the stomach that is necessary for vitamin B12 absorption.
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Enteropeptidase
Digestive enzyme secreted by cells in the duodenum. This enzyme converts trypsinogen to trypsin. Trypsin is then able to activate other pancreatic enzymes to allow digestion to continue within the duodenum.
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Bile
An alkaline fluid synthesized in the liver, stored in the gall bladder, and released. into the duodenum. Bile aids in the emulsification, digestion, and absorption of fats.
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Red Fibers
Slow-twitch muscle fibers. They are primarily aerobic and contain many mitochondria and high levels of myoglobin
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White Fibers
Fast-twitch muscle fibers. They are primarily anaerobic and fatigue more easily than red fibers
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Penetrance
The percentage of people in a population with a certain genotype who express the associated phenotype.
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Disruptive Selection
Type of natural selection where both phenotypic extremes are favored over the average phenotype.
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Archenteron
The central cavity in the gastrula stage of embryological development; it is lined by endoderm and ultimately gives rise to the adult digestive tract.
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Ductus Arteriosus
A shunt that connects the pulmonary artery to the aorta in order to bypass the fetal lung.
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Aldosterone
A steroid hormone produced in the adrenal cortex that is responsible for reabsorption of sodium and water and excretion of potassium and hydrogen ions.
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Intestinal Glands
Contains brush-border enzymes such as maltase, sucrase, and lactase to digest disaccharides. Other enzymes of these glands include aminopeptidase, dipeptidase, and enteropeptidase
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Episomes
Plasmids that have the ability to integrate into the host genome.
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Gastric Glands
Located in the stomach; secrete HCl and various enzymes (such as pepsin) when stimulated by gastrin.
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Cholecystokinin (CCK)
A hormone that is secreted by the duodenum in response to the presence of chyme. CCK stimulates the release of bile and pancreatic enzymes into the small intestine, and promotes satiety.
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Adrenal Medulla
Synthesizes and releases epinephrine and norepineprine, which stimulate an increase in the metabolic rate and blood glucose levels.
241
Blood Antigens
Proteins or sugars found on the erythrocyte cell surface. Three antigens used to differentiate blood groups are A, B, and Rh. If a host organism is transfused with erythrocytes containing antigens that the host does not have, an immune response will be triggered, leading to hemolysis.
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Lytic Cycle
Phase in viral replication in which the host cell is lysed and releases new virions. Contrast with the lysogenic cycle.
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Lysogenic Cycle
Phase of viral replication in which the DNA of the bacteriophage becomes integrated in the host's genome and replicates as the bacteria replicates. Contrast with the lytic cycle.
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Interstitial Cells
Also called Leydig cells, interstitial cells are located in the testes and secrete testosterone and other androgens.
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Thyroid Hormones
Synthesized and released by the thyroid gland, thyroid hormones triiodothyronine (T3) and thyroxine (T4) stimulate cellular respiration as well as protein and fatty acid synthesis and degradation.
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Proximal Convoluted Tubule
Portion of nephron where glucose, amino acids, and other important organic molecules are reabsorbed. The proximal convoluted tubules lie in the cortex of the kidney.
