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Glossary
Golgi apparatus
(GOAL-gee) cell organelle
consisting of fl attened membranous sacs;
usually near nucleus; processes newly
synthesized proteins for secretion or
distribution to other organelles
Golgi tendon organ
tension-sensitive
mechanoreceptor ending of afferent nerve
fi ber; wrapped around collagen bundles in
tendon
gonad
(GOH-nad) gamete-producing reproductive
organ—testes in male and ovaries in female
gonadal steroid
hormone synthesized in the
testes (testosterone) and ovaries (estrogen and
progesterone)
gonadotropic hormone
(goh-nad-oh-TROH-
pik) hormone secreted by anterior pituitary
that controls gonadal function; FSH or LH;
also called
gonadotropin
gonadotropin
glycoprotein hormone secreted by
pituitary (LH, FSH) and placenta (hCG) that
infl uence gonadal function
gonadotropin-releasing hormone (GnRH)
hypophysiotropic hormone that stimulates
LH and FSH secretion by anterior pituitary in
males and females
G protein
one protein from a family of regulatory
proteins that reversibly bind guanosine
nucleotides; plasma membrane G proteins
interact with membrane ion channels or enzymes
graafi
an follicle
(GRAF-ee-un) mature follicle
just before ovulation
graded potential
membrane potential change
of variable amplitude and duration that is
conducted decrementally; has no threshold or
refractory period
gradient
(GRAY-dee-ent) continuous increase or
decrease of a variable over distance
gram atomic mass
amount of element in grams
equal to the numerical value of its atomic weight
granulosa cell
(gran-you-LOH-sah) cell that
contributes to the layers surrounding egg and
antrum in ovarian follicle; secretes estrogen,
inhibin, and other messengers that infl uence
the egg
gray matter
area of brain and spinal cord that
appears gray in unstained specimens and
consists mainly of cell bodies and unmyelinated
portions of nerve fi bers
growth cone
tip of developing axon
growth factor
one of a group of peptides that
is highly effective in stimulating cell division
and/or differentiation of certain cell types
growth hormone (GH)
peptide hormone
secreted by anterior pituitary; stimulates
insulin-like growth factor I release; enhances
body growth by stimulating protein synthesis
growth hormone-releasing hormone
(GHRH)
hypothalamic peptide hormone
that stimulates growth hormone secretion by
anterior pituitary
growth-inhibiting factor
one of a group of
peptides that modulates growth by inhibiting
cell division in specifi c tissues
guanine (G)
(GWAH-neen) purine base in DNA
and RNA
guanosine triphosphate (GTP)
(GWAH-
noh-seen tri-FOS-fate) energy-transporting
molecule similar to ATP except that it contains
the base guanine rather than adenine
guanylyl cyclase
(GUAN-ah-lil) enzyme that
catalyzes transformation of GTP to cyclic GMP
gustation
(gus-TAY-shun) the sense of taste
gyrus
(JYE-rus) sinuous raised ridges on the outer
surface of the cerebral cortex
H
habituation
(hab-bit-you-A-shun) reversible
decrease in response strength upon repeatedly
administered stimulation
hair cell
mechanoreceptor in organ of Corti and
vestibular apparatus
heart
muscular pump that generates blood
pressure and fl ow in the cardiovascular system
heart rate
number of heart contractions per
minute
heart sound
noise that results from vibrations due
to closure of atrioventricular valves (fi rst heart
sound) or pulmonary and aortic valves (second
heart sound)
heavy chain
pair of large, coiled polypeptides
that makes up the rod and globular head of a
myosin molecule
helicotrema
outer point in the cochlea where the
scala vestibuli and scala tympani meet
helper T cell
T cell that, via secreted cytokines,
enhances the activation of B cells and cytotoxic
T cells
hematocrit
(heh-MAT-oh-krit) percentage of
total blood volume occupied by blood cells
hematopoietic growth factor (HGF)
(heh-
MAT-oh-poi-ET-ik) group of protein
hormones and paracrine agents that stimulate
proliferation and differentiation of various
types of blood cells
heme
(heem) iron-containing organic molecule
bound to each of the four polypeptide chains
of hemoglobin or to cytochromes
hemodynamics
the factors describing what
determines the movement of blood, in
particular, pressure, fl ow, and resistance
hemoglobin
(HEE-moh-gloh-bin) protein
composed of four polypeptide chains, each
attached to a heme; located in erythrocytes and
transports most blood oxygen
hemoglobin saturation
percent of hemoglobin
molecules combined with oxygen
hemorrhage
(HEM-er-age) bleeding
hemostasis
(hee-moh-STAY-sis) stopping blood
loss from a damaged vessel
Henle’s loop
see
loop of Henle
Henry’s law
amount of gas dissolved in a liquid is
proportional to the partial pressure of gas with
which the liquid is in equilibrium
heparin
(HEP-ah-rin) anticlotting agent
found on endothelial cell surfaces; binds
antithrombin III to tissues; used as an
anticoagulant drug
hepatic
(hih-PAT-ik) pertaining to the liver
hepatic portal vein
vein that conveys blood from
capillaries in the intestines and portions of the
stomach and pancreas to capillaries in the liver
hepatocyte
parenchymal cell of the liver
Hering-Breuer refl
ex
infl ation of the lung
stimulates afferent nerves, which inhibit the
inspiratory nerves in the medulla and thereby
help to terminate inspiration
hertz (Hz)
(hurts) cycles per second; measure
used for wave frequencies
heterozygous
(het-er-oh-ZY-gus) condition of
having maternal and paternal copies of a gene
with slightly different nucleotide sequences
(alleles);
compare
homozygous
hexose
a six-carbon sugar, like glucose
high-density lipoprotein (HDL)
lipid-protein
aggregate having low proportion of lipid;
promotes removal of cholesterol from cells
hippocampus
(hip-oh-KAM-pus) portion of
limbic system associated with learning and
emotions
histamine
(HISS-tah-meen) infl ammatory
chemical messenger secreted mainly by mast
cells; monoamine neurotransmitter
histone
class of proteins that participate in the
packaging of DNA within the nucleus; strands
of DNA form coils around the histones
homeostasis
(home-ee-oh-STAY-sis) relatively
stable condition of internal environment that
results from regulatory system actions
homeostatic control system
(home-ee-oh-
STAT-ik) collection of interconnected
components that keeps a physical or chemical
variable of internal environment within a
predetermined normal range of values
homeothermic
(home-ee-oh-THERM-ik)
capable of maintaining body temperature
within very narrow limits
homologous
(hoh-MAHL-ah-gus) corresponding
in origin, structure, and position
homozygous
(hoh-moh-ZY-gus) condition of
having maternal and paternal copies of a gene
with identical nucleotide sequences (alleles);
compare
heterozygous
horizontal cell
a specialized type of neuron
found in the retina of the eye that integrates
information from local photoreceptor cells
hormone
chemical messenger synthesized by
specifi c endocrine cells in response to certain
stimuli and secreted into the blood, which
carries it to target cells
hormone-sensitive lipase (HSL)
an enzyme
present in adipose tissue that acts to break
down triglycerides into glycerol and fatty acids,
which then enter the circulation; it is inhibited
by insulin and stimulated by catecholamines
human chorionic gonadotropin (hCG)
(kor-ee-
ON-ik go-NAD-oh-troh-pin) protein hormone
secreted by trophoblastic cells of embryo;
maintains secretory activity of corpus luteum
during fi rst 3 months of pregnancy
human placental lactogen
(plah-SEN-tal LAK-
toh-jen) hormone produced by placenta that
has effects similar to those of growth hormone
and prolactin
hydrochloric acid
(hy-droh-KLOR-ik) HCl;
strong acid secreted into stomach lumen by
parietal cells
hydrogen bond
weak chemical bond between
two molecules or parts of the same molecule,
in which negative region of one polarized
substance is electrostatically attracted to
a positively charged region of polarized
hydrogen atom in the other
hydrogen ion
(EYE-on) H
+
; single proton; H
+
concentration of a solution determines its
acidity
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