gamete (GAM-eet) An egg or sperm cell. gametogenesis (GAM-eh-toe-JEN-eh-sis) The production of eggs or sperm. gamma-(7-)aminobutyric acid (GABA) (ah-MEE-no-byu-TIRR-ic) An inhibitory neurotransmitter of the central nervous system in the biogenic amine class. fig. 12.18 gamma (7) globulins (GLOB-you-lins) A class of relatively large proteins found in the blood plasma and on the surfaces of immune cells, functioning as antibodies. See also globulin. ganglion (GANG-glee-un) A cluster of nerve cell bodies in the peripheral nervous system, often resembling a knot in a string. gangrene Tissue necrosis resulting from ischemia. gap junction A junction between two cells consisting of a pore surrounded by a ring of proteins in the plasma membrane of each cell, allowing solutes to diffuse from the cytoplasm of one cell to the next; functions include cell-to-cell nutrient transfer in the developing embryo and electrical communication between cells of cardiac and smooth muscle. See also electrical synapse. fig. 5.29 gastric Pertaining to the stomach. gate A protein channel in a cellular membrane that can open or close in response to chemical, electrical, or mechanical stimuli, thus controlling when substances are allowed to pass through the membrane. gene A segment of DNA that codes for the synthesis of one protein. gene locus The site on a chromosome where a given gene is located. generator potential A graded, reversible rise in the local voltage across the plasma membrane of a nerve or muscle cell in response to a stimulus; triggers an action potential if it reaches threshold. genetic engineering Any of several techniques that alter the genetic constitution of a cell or organism, including recombinant DNA technology and gene substitution therapy. genome (JEE-nome) All the genes of one individual, estimated at 35,000 genes in humans. genotype (JEE-no-type) The pair of alleles possessed by an individual at one gene locus on a pair of homologous chromosomes; strongly influences the individual's phenotype for a given trait.
germ cell A gamete or any precursor cell destined to become a gamete. germ layer Any of first three tissue layers of an embryo: ectoderm, mesoderm, or endoderm. gestation (jess-TAY-shun) Pregnancy. gland Any organ specialized to produce a secretion;
in some cases a single cell, such as a goblet cell. glaucoma (glaw-CO-muh) A visual disease in which an excessive amount of aqueous humor accumulates and creates pressure that is transmitted through the lens and vitreous body to the retina; pressure on the blood vessels of the choroid causes ischemia, retinal necrosis, and blindness. globulin (GLOB-you-lin) A globular protein such as an enzyme, antibody, or albumin; especially a family of proteins in the blood plasma that includes albumin, antibodies, fibrinogen, and pro-thrombin.
glomerular capsule (glo-MERR-you-lur) A doublewalled capsule around each glomerulus of the kidney; receives glomerular filtrate and empties into the proximal convoluted tubule. Also called Bowman's capsule. fig. 23.6 glomerulus A spheroid mass of blood capillaries in the kidney that filters plasma and produces glomerular filtrate, which is further processed to form the urine. fig. 23.6 glucagon (GLUE-ca-gon) A hormone secreted by a cells of the pancreatic islets in response to hypoglycemia; promotes glycogenolysis and other effects that raise blood glucose concentration. glucocorticoid (GLUE-co-COR-tih-coyd) Any hormone of the adrenal cortex that affects carbohydrate, fat, and protein metabolism; chiefly cortisol and corticosterone. gluconeogenesis (GLUE-co-NEE-oh-JEN-eh-sis) The synthesis of glucose from noncarbohydrates such as fats and amino acids. glucose A monosaccharide (C6H12O6) also known as blood sugar; glycogen, starch, cellulose, and maltose are made entirely of glucose, and glucose constitutes half of a sucrose or lactose molecule. The isomer involved in human physiology is also called dextrose. glucose-sparing effect An effect of fats or other energy substrates in which they are used as fuel by most cells, so that those cells do not consume glucose; this makes more glucose available to cells such as neurons that cannot use alternative energy substrates. glycerol (GLISS-er-ol) A viscous three-carbon alcohol that forms the structural backbone of triglyceride and phospholipid molecules; also called glycerin.
glycocalyx (GLY-co-CAY-licks) A layer of carbohydrate molecules covalently bonded to the phospholipid and protein molecules of a plasma membrane; forms a surface coat on all human cells. glycogen (GLY-co-jen) A glucose polymer synthesized by liver, muscle, uterine, and vaginal cells that serves as an energy-storage polysaccharide. glycogenesis (GLY-co-JEN-eh-sis) The synthesis of glycogen.
glycogenolysis (GLY-co-jeh-NOLL-ih-sis) The hydrolysis of glycogen, releasing glucose. glycolipid (GLY-co-LIP-id) A phospholipid molecule with a carbohydrate covalently bonded to it, found in the plasma membranes of cells.
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Physiology: The Unity of Companies, 2003 Form and Function, Third Edition
G-9 Glossary glycolysis (gly-COLL-ih-sis) A series of anaerobic oxidation reactions that break a glucose molecule into two molecules of pyruvic acid and produce a small amount of ATP. glycoprotein (GLY-co-PRO-teen) A protein molecule with a smaller carbohydrate covalently bonded to it; found in mucus and the glycocalyx of cells, for example.
glycosaminoglycan (GAG) (GLY-cose-am-ih-no-GLY-can) A polysaccharide composed of modified sugars with amino groups; the major component of a proteoglycan. GAGs are largely responsible for the viscous consistency of tissue gel and the stiffness of cartilage.
goblet cell A mucus-secreting gland cell, shaped somewhat like a wineglass, found in the epithelia of many mucous membranes. fig. 5.33 Golgi complex (GOAL-jee) An organelle composed of several parallel cisternae, somewhat like a stack of saucers, that modifies and packages newly synthesized proteins and synthesizes carbohydrates. fig. 3.27 Golgi vesicle A membrane-bounded vesicle pinched from the Golgi complex, containing its chemical product; may be retained in the cell as a lysosome or become a secretory vesicle that releases the product by exocytosis. gonad The ovary or testis. gonadotropin (go-NAD-oh-TRO-pin) A pituitary hormone that stimulates the gonads; specifically FSH and LH.
G protein A protein of the plasma membrane that is activated by a membrane receptor and, in turn, opens an ion channel or activates an intracellular physiological response; important in linking ligand-receptor binding to second-messenger systems. graded potential A variable change in voltage across a plasma membrane, as opposed to the all-or-none quality of an action potential. gradient A difference or change in any variable, such as pressure or chemical concentration, from one point in space to another; provides a basis for molecular movements such as gas exchange, osmosis, and facilitated diffusion, and for bulk movements such as blood flow and airflow. granulocyte (GRAN-you-lo-site) Any of three types of leukocytes (neutrophils, eosinophils, or basophils) with prominent cytoplasmic granules. granulosa cells Cells that form a stratified cuboidal epithelium lining an ovarian follicle; source of steroid sex hormones. fig. 28.14 gray matter A zone or layer of tissue in the central nervous system where the neuron cell bodies, dendrites, and synapses are found; forms the core of the spinal cord, nuclei of the brainstem, basal nuclei of the cerebrum, cerebral cortex, and cerebellar cortex. fig. 14.6 gross anatomy Bodily structure that can be observed without magnification. growth factor A chemical messenger that stimulates mitosis and differentiation of target cells that have receptors for it; important in such processes as fetal development, tissue mainte nance and repair, and hemopoiesis; sometimes a contributing factor in cancer. growth hormone (GH) A hormone of the anterior pituitary gland with multiple effects on many tissues, generally promoting tissue growth. guanine A double-ringed nitrogenous base (purine) found in DNA and RNA; one of the four bases of the genetic code; complementary to cytosine in the double helix of DNA. fig. 4.2 gyrus (JY-rus) A wrinkle or fold in the cortex of the cerebrum or cerebellum.
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