Biology Review and Vocabulary Part 8

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AIDS - The name of the late stages of HIV infection, defined by a specified reduction of T cells and the appearance of characteristic secondary infections.

B cell receptors-The antigen receptor on B cells: a Y-shaped, membrane-bound molecule consisting of two identical heavy chains and two identical light chains linked by disulfide bridges and containing two antigen-binding sites; also called a membrane immunoglobulin or membrane antibody.

B cells -A type of lymphocyte that develops to maturity in the bone marrow. After encountering antigen, B cells differentiate into antibody-secreting plasma cells, the effector cells of humoral immunity.

CD4 -A surface protein, present on most helper T cells, that binds to class II MHC molecules on antigen-presenting cells, enhancing the interaction between the T cell and the antigen-presenting cell.

CD8-A surface protein, present on most cytotoxic cells, that binds to class I MHC molecules on target cells, enhancing the interaction between the T cell and the target cell.

HIV -The infectious agent that causes AIDS. HIV is a retrovirus.

MHC -A family of genes that encode a large set of cell surface proteins called MHC molecules. Class I and class II MHC molecules function in antigen presentation to T cells. Foreign MHC molecules on transplanted tissue can trigger T cell responses that may lead to rejection of the transplant.

T cell receptors -The antigen receptor on T cells; a membrane-bound molecule consisting of one ? chain and one ? chain linked by a disulfide bridge and containing one antigen-binding site.

T cells -A type of lymphocyte, including the helper T cells and cytotoxic T cells, that develops to maturity in the thymus. After encountering antigen, T cells are responsible for cell-mediated immunity.

acquired immunity -The kind of defense that is mediated by B lymphocytes (B cells) and T lymphocytes (T cells). It exhibits specificity, memory, and self-nonself recognition. Also called adoptive immunity.

active immunity -Long-lasting immunity conferred by the action of a person’s B cells and T cells and the resulting B and T memory cells specific for a pathogn. Active immunity can develop as a result of natural infection or immunization.

anaphylactic shock   -An acute, whole-body, life-threatening, allergic response.

antibodies -A protein secreted by plasma cells (differentiated B cells) that binds to a particular antigen and marks it for elimination; also called immunoglobulin. All antibody molecules have the same Y-shaped structure and in their monomer form consist of two identical heavy chains and two identical light chains joined by disulfide bridges.

antigen -A macromolecule that elicits an immune response by lymphocytes.

antigen presentation -The process by which an MHC molecule binds to a fragment of an intracellular protein antigen and carries it to the cell surface, where it is displayed and can be recognized by a T cell.

antigen receptors -The general term for a surface protein, located on B cells and T cells, that binds to antigens, initiating acquired immune responses. The antigen receptors on B cells are called B cell receptors (or membrane immunoglobulins), and the antigen receptors on T cells are called T cell receptors.

autoimmune diseases -An immunological disorder in which the immune system turns against self.

cell mediated immune response -The branch of acquired immunity that involves the activation of cytotoxic T cells, which defend against infected cells, cancer cells, and transplanted cells.

chemokines -Any of about 50 different proteins, secreted by many cell types near a site of injury or infection, that help direct migration of white blood cells to an injury site and induces other changes central to inflammation.

clonal selection -The process by which an antigen selectively binds to and activates only those lymphocytes bearing receptors specific for the antigen. The selected lymphocytes proliferate and differentiate into a clone of effector cells and a clone of memory cells specific for the stimulating antigen. Clonal selection accounts for the specificity and memory of acquired immune responses.

complement system -A group of about 30 blood proteins that may amplify the inflammatory response, enhance phagocytosis, or directly lyse pathogens. The complement system is activated in a cascade initiated by surface antigens on microorganisms or by antigen-antibody complexes.

cytokines -Any of a group of proteins secreted by a number of cell types, including macrophages and helper T cells, that regulate the function of lymphocytes and other cells of the immune system.

dendritic cells -An antigen-presenting cell, located mainly in lymphatic tissues and skin, that is particularly efficient in presenting antigens to naive helper T cells, thereby initiating a primary immune response.

effector cells -A muscle cell or gland cell that performs the body’s responses to stimuli; responds to signals from the brain or other processing center of the nervous system.

eosinphils -A type of white blood cell with low phagocytic activity that is thought to play a role in defense against parasitic worms by releasing enzymes toxic to these invaders.

epitope -A small, accessible region of an antigen to which an antigen receptor or antibody binds; also called an antigenic determinant.

graft versus host reaction-An attack against a patient’s body cells by lymphocytes received in a bone marrow transplant.

heavy chains -One of the two types of polypeptide chains that make up an antibody molecule and B cell receptor; consists of a variable region, which contributes to the antigen-binding site, and a constant region.

helper T cell -A type of T cell that, when activated, secretes cytokines that promote the response of B cells (humoral response) and cytotonic T cells (cell-mediated response) to antigens.

histamine-A substance released by mast cells that causes blood vessels to dilate and become more permeable during an inflammatory response.

humoral immune response -The branch of acquired immunity that involves the activation of B cells and that leads to the production of antibodies, which defend against bacteria and viruses in body fluids.

immunization -The process of generating a state of immunity by artifical means. In active immunization, a nonpathogenic version of a normally pathogenic microbe is administered, inducing B and T cell responses and immunological memory. In passive immunization, antibodies specific for a particular microbe are administered, conferring immediate but temporary protection. Also called vaccination.

immunoglobins -Any of the class of proteins that function as antibodies. Immunoglobulins are divided into five major classes that differ in their distribution in the body and antigen disposal activities.

inflammatory response -A localized innate immune defense triggered by physical injury or infection of tissue in which changes to nearby small blood vessels enhance the infiltration of white blood cells, antimicrobial proteins, and clotting elements that aid in tissue repair and destruction of invading pathogens; may also involve systemic effects such as fever and increased production of white blood cells.

innate immunity -The kind of defense that is mediated by phagocytic cells, antimicrobial proteins, the inflammatory response, and natural killer (NK) cells. It is present before exposure to pathogens and is effective from the time of birth.

interferon -A protein that has antiviral or immune regulatory functions. Interferon ? and interferon-??, secreted by virus-infected cells, help nearby cells resist viral infection; interferon - secreted by T cells, helps activate macrophages.

light chains -One of the two types of polypeptide chains that make up an antibody molecule and B cell receptor; consists of a variable region, which contributes to the antigen-binding site, and a constant region.

lymphocytes -A type of white blood cell that mediates acquired immunity. Lymphocytes that complete their development in the bone marrow are called B cells, and those that mature in the thymus are called T cells.

lysozyme -An enzyme in sweat, tears, and saliva that attacks bacterial cell walls.

macrophages-A phagocytic cell present in many tissues that functions in innate immunity by destroying microbes and in acquired immunity as an antigen-presenting cell.

mast cells-A vertebrate body cell that produces histamine and other molecules that trigger the inflammatory response.

membrane attack complex-A molecular complex consisting of a set of complement proteins that forms a pore in the membrane of bacterial and transplanted cells, causing the cells to die by lysis.

memory cells -One of a clone of long-lived lymphocytes, formed during the primary immune response, that remains in a lymphoid organ until activated by exposure to the same antigen that triggered its formation. Activated memory cells mount the secondary immune response.

monoclonal antibodies -Any of a preparation of antibodies that have been produced by a single clone of cultured cells and thus are all specific for the same epitope.

monocytes-A type of white blood cell that migrates into tissues and develops into a macrophage.

natural killer cells -A type of white blood cell that can kill tumor cells and virus-infected cells; an important component of innate immunity.

netrophils-The most abundant type of white blood cell. Neutrophils are phagocytic and tend to self-destruct as they destroy foreign invaders, limiting their life span to a few days.

passive immunity -Short-term immunity conferred by the administration of ready-made antibodies or the transfer of maternal antibodies to a fetus or nursing infant; lasts only a few weeks or months because the immune system has not been stimulated by antigens.

phagocytosis-A type of endocytosis involving large, particulate substances, accomplished mainly by macrophages, neutrophils, and dendritic cells.

plasma cells -The antibody-secreting effector cell of humoral immunity; arises from antigen-stimulated B cells.

primary immune response -The initial acquired immune response to an antigen, which appears after a lag of about 10 to 17 days.

secondary immune response -The acquired immune response elicited on second or subsequent exposures to a particular antigen. The secondary immune response is more rapid, of greater magnitude, and of longer duration than the primary immune response.

thymus-A small organ in the thoracic cavity of vertebrates where maturation of T cells is completed.

vaccination-See immunization.

ANF - A peptide hormone that opposes the renin-angiotensin-aldosterone system (RAAS).

JGA- A specialized tissue located near the afferent arteriole that supplies blood to the glomerulus.

RAAS - A part of a complex feedback circuit that normally partners with antidiuretic hormone in osmoregulation.

afferent arteriole -The blood vessel supplying a nephron.

aldosterone -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.

ammonia -A small, very toxic molecule made up of three hydrogen atoms and one nitrogen atom; produced by nitrogen fixation and as a metabolic waste product of protein and nucleic acid metabolism.

angiotensin II -A hormone that stimulates constriction of precapillary arterioles and increases reabsorption of NaCl and water by the proximal tubules of the kidney, increasing blood pressure and volume.

anhydrobiosis -The ability to survive in a dormant state when an organism’s habitat dries up; also called cryptobiosis.

antideuritic hormone -A hormone produced in the hypothalamus and released from the posterior pituitary. It promotes water rentention by the kidneys as part of an elaborate feedback scheme that helps regulate the osmolarity of the blood.

bowmans 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.

coritical nephrons - Nephrons located almost entirely in the renal cortex. These nephrons have a reduced loop of Henle.

countercurrent multiplier systems - A countercurrent system in which energy is expended in active transport to facilitate exchange of materials and create concentration gradients. For example, the loop of Henle actively transports NaCl from the filtrate in the upper part of the ascending limb of the loop, making the urine-concentrating function of the kidney more effective.

distal tubule - In the vertebrate kidney, the portion of a nephron that helps refine filtrate and empties it into a collecting duct.

efferent arteriole - The blood vessel draining a nephron.

euryhaline - Referring to organisms that can tolerate substantial changes in external osmolarity.

excretion - The disposal of nitrogen-containing waste products of metabolism.

filtrate - Fluid extracted by the excretory system from the blood or body cavity. The excretory system produces urine from the filtrate after extracting valuable solutes from it and concentrating it.

filtration - In the vertebrate kidney, the extraction of water and small solutes, including metabolic wastes, from the blood by the nephrons.

glomerulus - A ball of capillaries surrounded by Bowman’s capsule in the nephron and serving as the site of filtration in the vertebrate kidney.

juxtamedullary nephrons - Nephrons with well-developed loops of Henle that extend deeply into the renal medulla.

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.

malpighian tubules - A unique excretory organ of insects that empties into the digestive tract, removes nitrogenous wastes from the blood, and functions in osmoregulation.

metanephridia - (plural, metanephridia) In annelid worms, a type of excretory tubule with internal openings called nephrostomes that collect body fluids and external openings called nephridiopores.

nephron - The tubular excretory unit of the vertebrate kidney.

osmoconformer - An animal that does not actively adjust its internal osmolarity because it is isotonic with its environment.

osmolarity - Solute concentration expressed as molarity.

osmoregulation - The regulation of solute and water concentrations in body fluids by organisms living in hyperosmotic, hypoosmotic, and terrestrial environments.

osmoregulator - An animal whose body fluids have a different osmolarity than the environment and that must either discharge excess water if it lives in a hypotonic environment or take in water if it inhabits a hypertonic environment.

peritubular cappillaries - The network of tiny blood vessels that surrounds the proximal and distal tubules in the kidney.

protonephridium - 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.

proximal tubule - In the vertebrate kidney, the portion of a nephron immediately downstream from Bowman’s capsule that conveys and helps refine filtrate.

renal artery - The blood vessel bringing blood to the kidney.

renal cortex - The outer portion of the vertebrate kidney.

renal medulla - The inner portion of the vertebrate kidney, beneath the renal cortex.

renal pelvis - Funnel-shaped chamber that receives processed filtrate from the vertebrate kidney’s collecting ducts and is drained by the ureter.

renal vein - The blood vessel draining the kidney.

secretion - (1) The discharge of molecules synthesized by a cell. (2) In the vertebrate kidney, the discharge of wastes from the blood into the filtrate from the nephron tubules.

selective reabsorption - The selective uptake of solutes from a filtrate of blood, coelomic fluid, or hemolymph in the excretory organs of animals.

stenohaline - Referring to organisms that cannot tolerate substantial changes in external osmolarity.

transport epithelium - One or more layers of specialized epithelial cells that regulate solute movements.

urea - A soluble nitrogenous waste excreted by mammals, most adult amphibians, and many marine fishes and turtles; produced in the liver by a metabolic cycle that combines ammonia with carbon dioxide.

ureter - A duct leading from the kidney to the urinary bladder.

urethra - A tube that releases urine from the body near the vagina in females and through the penis in males; also serves in males as the exit tube for the reproductive system.

uric acid - An insoluble precipitate of nitrogenous waste excreted by land snails, insects, birds, and some reptiles.

urinary bladder - The pouch where urine is stored prior to elimination.

vasa recta - The capillary system that serves the loop of Henle.



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