G-18
Glossary
Polarized
State of a plasma membrane of an unstimulated neuron or
muscle cell in which the inside of the cell is relatively negative in com-
parison to the outside; the resting state.
Polycythemia
(pol
0
e-si-the
9
me-ah) An abnormally high number of
erythrocytes.
Polymer
A substance of high molecular weight with long, chainlike mol-
ecules consisting of many similar (repeated) units.
Polypeptide
(pol
0
e-pep
9
tīd) A chain of amino acids.
Polyps
Benign mucosal tumors.
Polysaccharide
(pol
0
e-sak
9
ah-rīd) Literally, many sugars, a polymer of
linked monosaccharides; e.g., starch, glycogen.
Pons
(1) Any bridgelike structure or part; (2) the part of the brain stem
connecting the medulla with the midbrain, providing linkage between
upper and lower levels of the central nervous system.
Pore
Te surface opening of the duct of a sweat gland.
Positive feedback mechanisms
Feedback that tends to cause the level of
a variable to change in the same direction as an initial change.
Posterior pituitary
Neural part of pituitary gland; part of the neurohy-
pophysis.
Postganglionic neuron
(post
0
gan
0
gle-ah
9
nik) Autonomic motor neuron
that has its cell body in a peripheral ganglion and projects its axon to an
effector.
Potential energy
Stored or inactive energy.
Preganglionic neuron
Autonomic motor neuron that has its cell body
in the central nervous system and projects its axon to a peripheral
ganglion.
Presbyopia
(pres
0
be-o
9
pe-ah) A condition that results in the loss of near
focusing ability; typical onset is around age 40.
Pressure gradient
Difference in pressure (hydrostatic or osmotic) that
drives movement of fluid.
Primary active transport
A type of active transport in which the energy
needed to drive the transport process is provided directly by hydrolysis
of A±P.
Prime mover
Muscle that bears the major responsibility for effecting a
particular movement; an agonist.
Process
(1) Prominence or projection; (2) series of actions for a specific
purpose.
Progesterone
(pro-jes
9
ter-ōn) Hormone partly responsible for preparing
the uterus for the fertilized ovum.
Prolactin (PRL)
(pro-lak
9
tin) Adenohypophyseal hormone that stimu-
lates the breasts to produce milk.
Pronation
(pro-na
9
shun) Inward rotation of the forearm causing the
radius to cross diagonally over the ulna—palms face posteriorly.
Prophase
Te first stage of mitosis, consisting of coiling of the chromo-
somes accompanied by migration of the two daughter centrioles toward
the poles of the cell, and nuclear membrane breakdown.
Proprioceptor
(pro
0
pre-o-sep
9
tor) Receptor located in a joint, muscle,
or tendon; concerned with locomotion, posture, and muscle tone.
Prostaglandin
(pros
0
tah-glan
9
din) A lipid-based chemical messenger
synthesized by most tissue cells; acts locally as a paracrine.
Prostate
Accessory reproductive gland; produces one-third of semen
volume, including fluids that activate sperm.
Protein
(pro
9
tēn) Organic compound composed of carbon, oxygen,
hydrogen, and nitrogen; types include enzymes, structural components;
10–30% of cell mass.
Permeability
Tat property of membranes that permits passage of mol-
ecules and ions.
Peroxisomes
(pĕ-roks
9
ĭ-sōmz) Membranous sacs in cytoplasm contain-
ing powerful oxidase enzymes that use molecular oxygen to detoxify
harmful or toxic substances, such as free radicals.
Peyer’s patches
(pi
9
erz) Lymphoid organs located in the small intestine;
also called aggregated lymphoid nodules.
pH unit
(pe-āch) Te measure of the relative acidity or alkalinity of a
solution.
Phagocytosis
(fag
0
o-si-to
9
sis) Engulfing of foreign solids by (phagocytic)
cells.
Phagosome
(fag
9
o-sōm) Vesicle formed as a result of phagocytosis.
Pharmacological dose
A drug dose that is dramatically higher than nor-
mal levels of that substance (e.g., hormone) in the body.
Pharyngotympanic tube
±ube that connects the middle ear and the
pharynx. Also called auditory tube, eustachian tube.
Pharynx
(fayr
9
inks) Muscular tube extending from the region posterior
to the nasal cavities to the esophagus.
Phenotype
(fe
9
no-tīp) Observable expression of the genotype.
Phospholipid
(fos
0
fo-lip
9
id) Modified lipid, contains phosphorus.
Phosphorylation
A chemical reaction in which a phosphate molecule is
added to a molecule; for example, phosphorylation of ADP yields A±P.
Photoreceptor
(fo
0
to-re-sep
9
tor) Specialized receptor cells that respond
to light energy; rods and cones.
Physiological acidosis
(as
0
ĭ-do
9
sis) Arterial pH lower than 7.35 result-
ing from any cause.
Physiological dose
A drug dose that replicates normal levels of that sub-
stance (e.g., hormone) in the body. (
Compare with
Pharmacological dose.)
Physiology
(fiz
0
e-ol
9
o-je) Study of the function of living organisms.
Pineal gland (body)
(pin
9
e-al) A hormone-secreting part of the dien-
cephalon of the brain thought to be involved in setting the biological
clock and influencing reproductive function.
Pinocytosis
(pe
0
no-si-to
9
sis) Engulfing of extracellular fluid by cells.
Pituitary gland
(pĭ-tu
9
ih-tayr
0
e) Neuroendocrine gland located beneath
the brain that serves a variety of functions including regulation of go-
nads, thyroid, adrenal cortex, lactation, and water balance.
Placenta
(plah-sen
9
tah) ±emporary organ formed from both fetal and
maternal tissues that provides nutrients and oxygen to the developing
fetus, carries away fetal metabolic wastes, and produces the hormones of
pregnancy.
Plasma
(plaz
9
mah) Te nonliving fluid component of blood within which
formed elements and various solutes are suspended and circulated.
Plasma cells
Members of a B cell clone; effector B cells specialized to
produce and release antibodies.
Plasma membrane
Membrane, composed of phospholipids, cholesterol,
and proteins, that encloses cell contents; outer limiting cell membrane.
Platelet
(plāt
9
let) Cell fragment found in blood; involved in clotting.
Pleurae
(ploo
9
re) ±wo layers of serous membrane that line the thoracic
cavity and cover the external surface of the lung.
Pleural cavity
(ploo
9
ral) A potential space between the two layers of
pleura; contains a thin film of serous fluid.
Plexus
(plek
9
sus) A network of converging and diverging nerve fibers,
blood vessels, or lymphatics.
Polar molecules
Nonsymmetrical molecules that contain electrically
unbalanced atoms.
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