Glossary of Biology Ch. 41-49

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An enzyme found within the small intestine that splits off one amino acid at a time, beginning at the opposite end of the polypeptide containing a free carboxyl group.
A mixture of substances that is produced in the liver, stored in the gall bladder, and acts as a detergent to aid in the digestion and absorption of fats.
A lubricated ball of chewed food.
An enzyme found within the small intestine that splits off one amino acid at a time, beginning at the end of the polypeptide that has a free carboxyl group.
cholecystokinin (cck)
A hormone released from the walls of the duodenum in response to the presence of amino acids or fatty acids.
An enzyme found in the duodenum. It is specific for peptide bonds adjacent to certain amino acids.
The tubular portion of the vertebrate alimentary tract between the small intestine and the anus; functions mainly in water absorption and the formation of feces.
An enzyme found attached to the intestinal lining. It splits small peptides.
The first section of the small intestine, where acid chyme from the stomach mixes with digestive juices from the pancreas, liver, gallbladder, and gland cells of the intestinal wall.
The process that keeps tiny fat droplets from coalescing.
An organ that stores bile and releases it as needed into the small intestine.
A digestive hormone, secreted by the stomach, that stimulates the secretion of gastric juice.
hepatic portal vessel
A large circulatory channel that conveys nutrient-laden blood from the small intestine to the liver, which regulates the blood's nutrient content.
An enzyme that hydrolyzes fat molecules in the intestinal lumen.
(plural, microvilli) One of many fine, fingerlike projections of the epithelial cells in the lumen of the small intestine that increase its surface area.
A team of enzymes that hydrolyze DNA and RNA into their component nucleotides.
A gland with dual functions: The nonendocrine portion secretes digestive enzymes and an alkaline solution into the small intestine via a duct; the endocrine portion secretes the hormones insulin and glucagon into the blood.
An enzyme present in gastric juice that begins the hydrolysis of proteins.
The inactive form of pepsin that is first secreted by specialized (chief) cells located in gastric pits of the stomach.
pyloric sphincter
In the vertebrate digestive tract, a muscular ring that regulates the passage of food out of the stomach and into the small intestine.
salivary amylase
A salivary gland enzyme that hydrolyzes starch.
(singular, villus) (1) A fingerlike projection of the inner surface of the small intestine. (2) A fingerlike projection of the chorion of the mammalian placenta. Large numbers of villi increase the surface areas of these organs.
(plural, alveoli) (1) One of the deadend, multilobed air sacs that constitute the gas exchange surface of the lungs. (2) One of the milk-secreting sacs of epithelial tissue in the mammary glands.
A vessel that conveys blood between an artery and a capillary bed.
A vessel that carries blood away from the heart to organs throughout the body.
AV node
A region of specialized muscle tissue between the right atrium and right ventricle. It generates electrical impulses that primarily cause the ventricles to contract.
atrioventricular valve
A valve in the heart between each atrium and ventricle that prevents a backflow of blood when the ventricles contract.
(plural, atria) A chamber that receives blood returning to the vertebrate heart.
(plural, bronchi) One of a pair of breathing tubes that branch from the trachea into the lungs.
Fine branches of the bronchus that transport air to alveoli.
capillary bed
A network of capillaries that infiltrate every organ and tissue in the body.
A microscopic blood vessel that penetrates the tissues and consists of a single layer of endothelial cells that allows exchange between the blood and interstitial fluid.
countercurrent exchange
The opposite flow of adjacent fluids that maximizes transfer rates; for example, blood in the gills flows in the opposite direction in which water passes over the gills, maximizing oxygen uptake and carbon dioxide loss.
The stage of the heart cycle in which the heart muscle is relaxed, allowing the chambers to fill with blood.
A red blood cell; contains hemoglobin, which functions in transporting oxygen in the circulatory system.
A hormone produced in the kidney when tissues of the body do not receive enough oxygen. This hormone stimulates the production of erythrocytes.
The activated form of the blood-clotting protein fibrinogen, which aggregates into threads that form the fabric of the clot.
The inactive form of the plasma protein that is converted to the active form fibrin, which aggregates into threads that form the framework of a blood clot.
An iron-containing protein in red blood cells that reversibly binds oxygen.
high-density lipoprotein (HDL)
A cholesterol-carrying particle in the blood, made up of cholesterol and other lipids surrounded by a single layer of phospholipids in which proteins are embedded. An HDL particle carries less cholesterol than a related lipoprotein, LDL, and may be correlated with a decreased risk of blood bvessel blockage.
A white blood cell; typically functions in immunity, such as phagocytosis or antibody production.
low-density lipoprotein (LDL)
cholesterol-carrying particle in the blood, made up of cholesterol and other lipids surrounded by a single layer of phospholipids in which proteins are embedded. An LDL particle carries the blood correlate with a tendency to develop blocked blood vessels and heart disease.
The colorless fluid, derived from interstitial fluid, in the lymphatic system of vertebrate animals.
An oxygen-storing, pigmented protein in muscle cells.
A small enucleated blood cell important in blood clotting; derived from large cells in the bone marrow.
pluripotent stem cell
cell within bone marrow that is a progenitor for any kind of blood cell.
semilunar valve
A valve located at the two exits of the heart, where the aorta leaves the left ventricle and the pulmonary artery leaves the right ventricle.
A specialized region of the right atrium of the mammalian heart that sets the rate of contraction; also called the sinoatrial (SA) node.
The stage of the heart cycle in which the heart muscle contracts and the chambers pump blood.
A clump of platelets and fibrin that block the flow of blood through a blood vessel.
active immunity
Immunity conferred by recovering from an infectious disease.
The name of the late stages of HIV infection; defined by a specified reduction of T cells and the appearance of characteristic secondary infections.
anaphylactic shock
An acute, life-threatening, allergic response.
An antigen-binding immunoglobulin, produced by B cells, that functions as the effector in an immune response.
antigen presentation
The process by which an MHC molecule cradles a fragment of an intracellular protein antigen in its hammocklike groove, carries it to the cell surface, and "presents" the protein to an antigen receptor on a nearby T cell.
antigen receptor
Transmembrane versions of antibody molecules that B cells and T cells use to recognize specific antigens. Also called membrane antibodies.
antigen-presenting cell (APCs)
Cells that ingest bacteria and viruses and then destroy them. Class II MHC molecules in these cells collect peptide remnants of this degradation and present them to helper T cells.
B lymphocyte (B cell)
A type of lymphocyte that develops in the bone marrow and later produces antibodies, which mediate humoral immunity.
A foreign macromolecule that does not belong to the host organism and that elicits an immune response.
A circulating leukocyte that produces histamine.
A T cell surface protein, present on most helper T cells, CD4 binds to part of the class II MHC protein.
cell-mediated immunity
The type of immunity that functions in defense against fungi, protists, bacteria, and viruses inside host cells and against tissue transplants, with highly specialized cells that circulate in the blood and lymphoid tissue.
A group of about 50 different proteins secreted by blood vessel endothelial cells and monocytes. These molecules bind to receptors on many types of leukocytes and induce numerous changes central to inflammation.
class I MHC molecules
A collection of cell surface glycoproteins encoded by a family of genes called the major histocompatibility complex. In humans, these glycoproteins are also known as the HLA, human leukocyte antigens. Class I MHC molecules are found on all nucleated cells.
class II MHC molecules
collection of cell surface glycoproteins encoded by a family of genes called the major histocompatibility complex. In humans, these glycoproteins are also known as the HLA, human leukocyte antigens. Class II MHC molecules are restricted to a few specialized cell types.
In the vertebrate immune system, protein factors secreted by macrophages and helper T cells as regulators of neighboring cells.
cytotoxic T cell (TC)
type of lymphocyte that kills infected cells and cancer cells.
helper T cell (TH)
A type of T cell that is required by some B cells to help them make antibodies or that helps other T cells respond to antigens or secrete lymphokines or interleukins.
A substance released by injured cells that causes blood vessels to dilate during an inflammatory response.
humoral immunity
The type of immunity that fights bacteria and viruses in body fluids with antibodies that circulate in blood plasma and lymph, fluids formerly called humors.
A chemical messenger of the immune system, produced by virus-infected cells and capable of helping other cells resist the virus.
interleukin-1 (IL-1)

interleukin-2 (IL-2)
A cytokine secreted by a macrophage that is in the process of phagocytizing and presenting antigen. IL-1, in combination with the antigen, activates the helper T cell to produce IL-2 and other cytokines.

A cytokine that helps B cells that have contacted antigen differentiate into antibody-secreting plasma cells.
natural killer (NK) cell
A nonspecific defensive cell that attacks tumor cells and destroys infected body cells, especially those harboring viruses.
The most abundant type of leukocyte. Neutrophils tend to self-destruct as they destroy foreign invaders, limiting their life span to but a few days.
An immune response in which the binding of antibodies to the surface of a microbe facilitates phagocytosis of the microbe by a macrophage.
A protein secreted by a cytotoxic T cell that lyses (ruptures) an infected cell by perforating its membrane.
T lymphocyte (T cell)
A type of lymphocyte responsible for cell-mediated immunity that differentiates under the influence of the thymus.
T-independent antigen
Antigens that can stimulate antibody production without the help of IL-2.
T-dependent antigen
Antigens that can stimulate antibody production only with help from T helper cells. Most protein antigens are T-dependent.
An adrenal hormone that acts on the distal tubules of the kidney to stimulate the reabsorption of sodium (Na+) and the passive flow of water from the filtrate.
antidiuretic hormone
A hormone that is part of an elaborate feedback scheme that helps regulate the osmolarity of the blood.
Bowman's capsule
A cup-shaped receptacle in the vertebrate kidney that is the initial, expanded segment of the nephron where filtrate enters from the blood.
collecting duct
The location in the kidney where filtrate from renal tubules is collected; the filtrate is now called urine.
distal tubule
In the vertebrate kidney, the portion of a nephron that helps refine filtrate and empties it into a collecting duct.
A ball of capillaries surrounded by Bowman's capsule in the nephron and serving as the site of filtration in the vertebrate kidney.
loop of Henle
The long hairpin turn, with a descending and ascending limb, of the renal tubule in the vertebrate kidney; functions in water and salt reabsorption.
An animal that does not actively adjust its internal osmolarity because it is isotonic with its environment.
Specialized cells of Bowman's capsule that are permeable to water and small solutes but not to blood cells or large molecules such as plasma proteins.
A soluble form of nitrogenous waste excreted by mammals and most adult amphibians.
An excretory system, such as the flame-cell system of flatworms, consisting of a network of closed tubules having external openings called nephridiopores and lacking internal openings.
malpighian tubule
unique excretory organ of insects that empties into the digestive tract, removes nitrogenous wastes from the blood, and functions in osmoregulation.
islets of Langerhans
Clusters of endocrine cells that secrete glucagon and insulin directly into the bloodstream.
The process of cytokinesis in animal cells, characterized by pinching of the plasma membrane; specifically, the succession of rapid cell divisions without growth during early embryonic development that converts the zygote into a ball of cells.
An embryonic stage in mammals; a hollow ball of cells produced one week after fertilization in humans.
An embryonic stage in mammals; a hollow ball of cells produced one week after fertilization in humans.
Leydig cell
Located between the seminiferous tubules of the testes, these cells produce testosterone and other androgens.
Increased muscle tension.
ovarian cycle
The cyclic recurrence of the follicular phase, ovulation, and the luteal phase in the mammalian ovary, regulated by hormones.
A type of reproduction in which females produce offspring from unfertilized eggs.
luteal phase
That portion of the ovarian cycle during which endocrine cells of the corpus luteum secrete female hormones.

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