G-8 Glossarythe thyroid gland by autoantibodies. It is associated
with exophthalmos (bulging eyes), high pulse
rate, high metabolic rate, and other symptoms of
hyperthyroidism.
gray matter The part of the central nervous system
that contains neuron cell bodies and dendrites but
few myelinated axons. It forms the cortex of the
cerebrum, cerebral nuclei, and the central region of
the spinal cord.
growth hormone (GH) A hormone secreted by
the anterior pituitary that stimulates growth of the
skeleton and soft tissues during the growing years
and that influences the metabolism of protein,
carbohydrate, and fat throughout life.
gustducins (gus-doo 9 sinz) The G-proteins involved
in the sense of taste, particularly of sweet and bitter
tastes.
gyrus (ji 9 rus) A fold or convolution in the
cerebrum.H
hair cells Sensory epithelial cells with processes
called hairs (cilia or stereocilia) on their apical
surfaces. These are mechanoreceptors involved in
equilibrium and hearing, where bending of the hairs
results in stimulation of associated sensory neurons.
haploid (hap 9 loid) Denoting cells that have one of
each chromosome type and therefore half the number
of chromosomes present in most other body cells.
Only the gametes (sperm and ova) are haploid.
hapten (hap 9 ten) A small molecule that is not
antigenic by itself, but which—when combined with
proteins—becomes antigenic and thus capable of
stimulating the production of specific antibodies.
haversian (h ̆a-ver 9 shan) system A haversian canal
and its concentrically arranged layers, or lamellae,
of bone. It constitutes the basic structural unit of
compact bone.
hay fever A seasonal type of allergic rhinitis
caused by pollen. It is characterized by itching and
tearing of the eyes, swelling of the nasal mucosa,
attacks of sneezing, and often by asthma.
hCG Human chorionic gonadotropin (kor 9 e-on-ik
gon-ad 0 ̆o-tro 9 pin) A hormone secreted by the embryo
that has LH-like actions and that is required for
maintenance of the mother’s corpus luteum for the
first 10 weeks of pregnancy.
HCN channels Cardiac pacemaker channels that
open in response to hyperpolarization and to cyclic
nucleotides, specifically to cyclic AMP produced
in response to catecholamines. The HCN channels
open at the end of an action potential to help produce
a diastolic depolarization, which serves as the
stimulus for the next action potential. By stimulating
these channels to produce a faster depolarization,
epinephrine and norepinephrine induce a faster
cardiac rate.
heart murmur An abnormal heart sound caused
by an abnormal flow of blood in the heart. Murmurs
are due to structural defects, usually of the valves or
septum.
heart sounds The sounds produced by closing of
the AV valves of the heart during systole (the first
sound) and by closing of the semilunar valves of
the aorta and pulmonary trunk during diastole (the
second sound).
helper T cells A subpopulation of T cells (lympho-
cytes) that help to stimulate antibody production of B
lymphocytes by antigens.
hematocrit (he-mat 9 ̆o-krit) The ratio of packed red
blood cells to total blood volume in a centrifuged
sample of blood, expressed as a percentage.highly branched chains of glucose subunits than does
plant starch.
glycogenesis (gli 0 k ̆o-jen 9 ̆ı-sis) The formation of
glycogen from glucose.
glycogenolysis (gli 0 ko-j ̆e-nol 9 ̆ı-sis) The hydrolysis
of glycogen to glucose-1-phosphate, which can be
converted to glucose-6-phosphate. The glucose-6-
phosphate then may be oxidized via glycolysis or (in
the liver) converted to free glucose.
glycolysis (gli 0 kol 9 ̆ı-sis) The metabolic pathway
that converts glucose to pyruvic acid. The final
products are two molecules of pyruvic acid and
two molecules of reduced NAD, with a net gain
of two ATP molecules. In anaerobic metabolism,
the reduced NAD is oxidized by the conversion of
pyruvic acid to lactic acid. In aerobic respiration,
pyruvic acid enters the Krebs cycle in mitochondria,
and reduced NAD is ultimately oxidized by oxygen
to yield water.
glycosuria (gli 0 k ̆o-soor 9 e- ̆a) The excretion of
an abnormal amount of glucose in the urine (urine
normally contains only trace amounts of glucose).
Golgi (gol 9 je) complex A network of stacked,
flattened membranous sacs within the cytoplasm
of cells. Its major function is to concentrate and
package proteins within vesicles that bud off from it.
Also called Golgi apparatus.
Golgi tendon organ A tension receptor in the
tendons of muscles that becomes activated by the
pull exerted by a muscle on its tendons; also called a
neurotendinous receptor.
gonad (go 9 nad) A collective term for testes and
ovaries.
gonadotropic (go 0 nad- ̆o-trop 9 ik) hormones
Hormones of the anterior pituitary that stimulate
gonadal function—the formation of gametes and
secretion of sex steroids. The two gonadotropins
are FSH (follicle-stimulating hormone) and LH
(luteinizing hormone), which are essentially the same
in males and females.
G-protein An association of three membrane-
associated protein subunits, designated alpha,
beta, and gamma, that is regulated by guanosine
nucleotides (GDP and GTP). The G-protein subunits
dissociate in response to a membrane signal and, in
turn, activate other proteins in the cell.
G-protein-coupled receptors This term refers to
receptor proteins in the plasma membrane that are
(1) specific for their regulatory ligands, including
neurotransmitters and hormones, and (2) coupled to
a complex of G-proteins. When the receptor binds to
its specific ligand, the G-protein complexes attached
to the receptor disassociate, and one or more of
their subunits travel in the membrane to activate a
different protein, such as an enzyme or ion channel.
graafian (graf 9 e-an) follicle A mature ovarian
follicle, containing a single fluid-filled cavity, with
the ovum located toward one side of the follicle and
perched on top of a hill of granulosa cells.
graded potential A change in the membrane
potential (depolarization or hyperpolarization)
with amplitudes that are varied, or graded, by
gradations in the stimulus intensity. The stimuli
for graded potentials in postsynaptic neurons are
neurotransmitters, and the degree of depolarization or
hyperpolarization produced depends on the amount
of neurotransmitter molecules released by the
presynaptic axons.
granular leukocytes (loo 9 k ̆o-s ̄ıts) Leukocytes
with granules in the cytoplasm. On the basis of the
staining properties of the granules, these cells are of
three types: neutrophils, eosinophils, and basophils.
Graves’ disease A hyperthyroid condition
believed to be caused by excessive stimulation ofchemically regulated (by neurotransmitters) or
voltage regulated (in which case they open in
response to a threshold level of depolarization).
general adaptation syndrome (GAS) The specific
response of the body to nonspecific stressors,
involving the activation of the hypothalamus-
pituitary-adrenal axis.
generator (jen 9 ̆e-ra 0 tor) potential The graded
depolarization produced by stimulation of a sensory
receptor that results in the production of action
potentials by a sensory neuron; also called the
receptor potential.
genetic (j ̆e-net 9 ik) recombination The formation
of new combinations of genes, as by crossing-over
between homologous chromosomes.
genetic transcription The process by which RNA
is produced with a sequence of nucleotide bases that
is complementary to a region of DNA.
genetic translation The process by which proteins
are produced with amino acid sequences specified by
the sequence of codons in messenger RNA.
genome (je 9 nom) All of the genes of an individual
or in a particular species.
ghrelin (gre 9 lin) A hormone secreted by the
stomach. Secretion of ghrelin rises between meals
and stimulates centers in the hypothalamus to
promote hunger.
gigantism (ji-gan 9 tiz 0 em) Abnormal body growth
due to the excessive secretion of growth hormone.
glomerular (glo-mer 9 y ̆u-lar) filtration rate (GFR)
The volume of blood plasma filtered out of the
glomeruli of both kidneys each minute. The GFR is
measured by the renal plasma clearance of inulin.
glomerular ultrafiltrate Fluid filtered through
the glomerular capillaries into the glomerular
(Bowman’s) capsule of the kidney tubules.
glomeruli (glo-mer 9 y ̆u-li) The tufts of capillaries in
the kidneys that filter fluid into the kidney tubules.
glomerulonephritis (glo-mer 0 y ̆u-lo-n ̆e-fri 9 tis)
Inflammation of the renal glomeruli; associated
with fluid retention, edema, hypertension, and the
appearance of protein in the urine.
glucagon (gloo 9 c ̆a-gon) A polypeptide hormone
secreted by the alpha cells of the islets of Langerhans
in the pancreas that acts to promote glycogenolysis
and raise the blood glucose levels.
glucocorticoid (gloo 0 ko-kor 9 t ̆ı-koid) Any of a
class of steroid hormones secreted by the adrenal
cortex (corticosteroids) that affects the metabolism
of glucose, protein, and fat. These hormones also
have anti-inflammatory and immunosuppressive
effects. The major glucocorticoid in humans is
hydrocortisone (cortisol).
gluconeogenesis (gloo 0 ko-ne 0 ̆o-jen 9 ̆ı-sis) The
formation of glucose from noncarbohydrate
molecules, such as amino acids, lactic acid, and
glycerol.
GLUT An acronym for glucose transporters.
GLUT proteins promote the facilitated diffusion of
glucose into cells. One isoform of GLUT, designated
GLUT4, is inserted into the cell membranes of
muscle and adipose cells in response to insulin
stimulation and exercise.
glutamate (gloo 9 t ̆a-m ̄at) The ionized form of
glutamic acid, an amino acid that serves as the major
excitatory neurotransmitter of the CNS. Glutamate
and glutamic acid are terms that can be used
interchangeably.
glutathione (gloo 0 tah-thi 9 on) A tripeptide molecule
that functions as the major cellular antioxidant.
glycogen (gli 9 k ̆o-jen) A polysaccharide of
glucose—also called animal starch—produced
primarily in the liver and skeletal muscles. Similar to
plant starch in composition, glycogen contains morefox36375_glo_G1-G19.indd 8fox36375_glo_G1-G19.indd 8 2/4/15 12:29 PM2/4/15 12:29 PM