738
Glossary
progesterone
(proh-JES-ter-own) steroid
hormone secreted by corpus luteum and
placenta; stimulates uterine gland secretion,
inhibits uterine smooth-muscle contraction,
and stimulates breast growth
program
related sequence of neural activity
preliminary to motor act
prohormone
peptide precursor from which are
cleaved one or more active peptide hormones
prokaryotic cell
cell such as a bacterium that
does not contain its genetic information
within a membrane-enclosed nucleus
prolactin
(pro-LAK-tin) peptide hormone
secreted by anterior pituitary; stimulates milk
secretion by mammary glands
prolactin-inhibiting hormone (PIH)
dopamine, which serves as a
hypophysiotropic hormone to inhibit
prolactin secretion by anterior pituitary
prolactin-releasing factor
putative
hypothalamic factor that stimulates prolactin
release
proliferative phase
(pro-LIF-er-ah-tive) stage
of menstrual cycle between menstruation and
ovulation during which endometrium repairs
itself and grows
promoter
specifi c nucleotide sequence at
beginning of gene that controls the initiation
of gene transcription; determines which of
the paired strands of DNA is transcribed into
RNA
propagation
(prop-ah-GAY-shun) conduction
of nerve impulse
proprioception
(PROH-pree-oh-cep-shun)
sense of posture and position; sensory
information dealing with the position of the
body in space and its parts relative to one
another
prostacyclin (PGI
2
)
eicosanoid that inhibits
platelet aggregation in blood clotting; also
called prostaglandin I
2
(PGI
2
)
prostaglandin
(pros-tah-GLAN-din) one class
of a group of modifi ed unsaturated fatty
acids (eicosanoids) that function mainly as
paracrine or autocrine agents
prostate gland
(PROS-tate) large gland
encircling urethra in the male; secretes
seminal fl uid into urethra
protease
(PROH-tee-ase) an enzyme capable of
breaking peptide bonds in a protein
proteasome
a complex of proteins capable of
denaturing (unfolding) other proteins and
assisting in protein degradation
protein
large polymer consisting of one or more
sequences of amino acid subunits joined by
peptide bonds
protein binding site
see
binding site
protein C
plasma protein that inhibits clotting
protein kinase
(KY-nase) any enzyme that
phosphorylates other proteins by transferring
to them a phosphate group from ATP
protein kinase C
enzyme that phosphorylates
certain intracellular proteins when activated
by diacylglycerol
proteolysis
the process whereby peptides and
proteins are cleaved into smaller molecules,
by the actions of specifi c enzymes (proteases)
proteolytic
(proh-tee-oh-LIT-ik) breaks down
protein
prothrombin
(proh-THROM-bin) inactive
precursor of thrombin; produced by liver and
normally present in plasma
proton
(PROH-tahn) positively charged
subatomic particle
proximal
(PROX-sih-mal) nearer; closer to
reference point;
compare
distal
proximal tubule
fi rst tubular component of a
nephron after Bowman’s capsule; comprises
convoluted
and
straight segments
puberty
attainment of sexual maturity when
conception becomes possible; as commonly
used, refers to 3 to 5 years of sexual
development that culminates in sexual maturity
pulmonary
(PUL-mah-nar-ee) pertaining to
lungs
pulmonary artery
large, branching vessel
carrying oxygen-poor blood away from the
heart toward the lungs
pulmonary circulation
circulation through
lungs; portion of cardiovascular system
between pulmonary trunk, as it leaves the
right ventricle, and pulmonary veins, as they
enter the left atrium
pulmonary stretch receptor
afferent nerve
ending lying in airway smooth muscle and
activated by lung infl ation
pulmonary surfactant
see
surfactant
pulmonary trunk
large artery that carries
blood from right ventricle of heart to lungs
pulmonary valve
valve between right ventricle
of heart and pulmonary trunk
pulmonary vein
large, converging vessel that
returns oxygen-rich blood toward the heart
from the lungs
pulse pressure
difference between systolic and
diastolic arterial blood pressures
pupil
opening in iris of eye through which light
passes to reach retina
purine
(PURE-ene) double-ring, nitrogen-
containing subunit of nucleotide; adenine or
guanine
Purkinje fi
ber
(purr-KIN-gee) specialized
myocardial cell that constitutes part of
conducting system of heart; conveys
excitation from bundle branches to
ventricular muscle
P wave
component of electrocardiogram
refl ecting atrial depolarization
pyloric sphincter
(py-LOR-ik) ring of smooth
muscle between stomach and small intestine
pyramidal cell
large neuron with characteristic
pyramid-shaped cell body and apical dendrite
pyramidal system
descending nervous system
pathways that originate in the cerebral
cortex, cross over the midline in the medulla,
and control fi ne movements of the distal
extremities
pyramidal tract
see
corticospinal pathway
pyrimidine
(pi-RIM-ih-deen) single-ring,
nitrogen-containing subunit of nucleotide;
cytosine, thymine, or uracil
pyrogen
see
endogenous pyrogen
pyruvate
(PY-roo-vayt) anion formed when
pyruvic acid loses a hydrogen ion
pyruvic acid
(py-ROO-vik) three-carbon
intermediate in glycolysis that, in absence of
oxygen, forms lactic acid or, in presence of
oxygen, enters Krebs cycle
Q
QRS complex
component of electrocardiogram
corresponding to ventricular depolarization
quaternary protein structure
formed when
two or more proteins associate with each
other by hydrogen bonds and other forces;
the individual proteins are then termed
subunits
R
radiation
emission of heat from the surface of an
object
rapid eye movement sleep
see
REM sleep
rapidly adapting receptor
sensory receptor that
fi res for a brief period at the onset and/or
offset of a stimulus
rate-limiting enzyme
enzyme in metabolic
pathway most easily saturated with substrate;
determines rate of entire metabolic pathway
rate-limiting reaction
slowest reaction in
metabolic pathway; catalyzed by rate-limiting
enzyme
reactant
(ree-AK-tent) molecule that enters
a chemical reaction; called the substrate in
enzyme-catalyzed reactions
reaction
see
chemical reaction
reactive hyperemia
(hy-per-EE-me-ah) transient
increase in blood fl ow following release of
occlusion of blood supply
receptive fi
eld
(or neuron) area of body that, if
stimulated, results in activity in that neuron
receptive relaxation
relaxation of the smooth
muscles of the stomach (fundus and body)
when food is swallowed; mediated by
parasympathetic nerves in the enteric nerve
plexuses
receptor
(in sensory system) specialized peripheral
ending of afferent neuron, or separate cell
intimately associated with it, that detects
changes in some aspect of environment; (in
intercellular chemical communication) specifi c
binding site in plasma membrane or interior
of target cell with which a chemical messenger
combines to exert its effects
receptor activation
change in receptor
conformation caused by combination of
messenger with receptor
receptor desensitization
temporary inability of a
receptor to respond to its ligand due to prior
ligand binding
receptor-mediated endocytosis
the specifi c
uptake of ligands in the extracellular fl uid
by regions of the plasma membrane that
invaginate and form intracellular vesicles
receptor potential
graded potential that arises in
afferent neuron ending, or a specialized cell
intimately associated with it, in response to
stimulation
receptor tyrosine kinase
the major type of
receptor protein that is itself an enzyme;
these receptors are on plasma membranes
and respond to many different water-soluble
chemical messengers
reciprocal innervation
inhibition of motor
neurons activating muscles whose contraction
would oppose an intended movement
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