736
Glossary
paracellular pathway
the space between adjacent
cells of an epithelium through which some
molecules diffuse as they cross the epithelium
paracrine agent
(PAR-ah-krin) chemical
messenger that exerts its effects on cells near
its secretion site; by convention, excludes
neurotransmitters;
compare
autocrine agent
paradoxical sleep
see
REM sleep
parasympathetic division
(par-ah-sim-pah-
THET-ik) portion of autonomic nervous
system whose preganglionic fi bers leave CNS
from brainstem and sacral portion of spinal
cord; most of its postganglionic fi bers release
acetylcholine;
compare
sympathetic division
parathyroid gland
one of four parathyroid-
hormone secreting glands on thyroid gland
surface
parathyroid hormone (PTH)
peptide hormone
secreted by parathyroid glands; regulates
calcium and phosphate concentrations of
extracellular fl uid
parietal cell
(pah-RY-ih-tal) gastric gland cell that
secretes hydrochloric acid and intrinsic factor
parietal lobe
region of cerebral cortex containing
sensory cortex and some association cortex
parietal pleura
(pah-RYE-it-al plu-rah) serous
membranes covering the inside of the chest
wall, the diaphragm, and the mediastinum
partial pressure (
P
)
that part of total gas pressure
due to molecules of one gas species; measure of
concentration of a gas in a gas mixture
parturition
events leading to and including
delivery of infant
passive immunity
resistance to infection resulting
from direct transfer of antibodies or sensitized
T cells from one person (or animal) to another;
compare
active immunity
pathway
series of connected nerves that move a
particular type of information from one part of
the brain to another part
pentose
any fi ve carbon monosaccharide
pepsin
(PEP-sin) family of several protein-
digesting enzymes formed in the stomach;
breaks protein down to peptide fragments
pepsinogen
(pep-SIN-ah-jen) inactive precursor
of pepsin; secreted by chief cells of gastric
mucosa
peptide
(PEP-tide) short polypeptide chain; by
convention, having less than 50 amino acids
peptide bond
polar covalent chemical bond
joining the amino and carboxyl groups of two
amino acids; forms protein backbone
peptide hormone
any of a family of hormones,
like insulin, composed of approximately two
to 50 amino acids; generally soluble in acid,
unlike larger protein hormones, which are
insoluble
peptidergic
neuron that releases peptides
percent hemoglobin saturation
see
hemoglobin
saturation
perception
understanding of objects and events
of external world that we acquire from neural
processing of sensory information
perforin
protein secreted by cytotoxic T cells;
forms channels in plasma membrane of target
cell, which destroys it
perfusion
blood fl ow
pericardium
(per-ah-KAR-dee-um) connective-
tissue sac surrounding heart
perimenopause
beginning period leading to
cessation of menstruation
peripheral chemoreceptor
carotid or aortic
body; responds to changes in arterial blood P
O
2
and H
+
concentration
peripheral membrane protein
hydrophilic
proteins associated with cytoplasmic surface of
cell membrane
peripheral nervous system
nerve fi bers extending
from CNS
peripheral thermoreceptor
cold or warm
receptor in skin or certain mucous membranes
peripheral vein
blood vessel outside the chest
cavity that returns blood from capillaries
toward the heart
peristaltic wave
(per-ih-STAL-tik) progressive
wave of smooth muscle contraction and
relaxation that proceeds along wall of a tube,
compressing the tube and causing its contents
to move
peritoneum
(per-ih-toh-NEE-um) membrane
lining abdominal and pelvic cavities and
covering organs there
peritubular capillary
capillary closely associated
with renal tubule
permeability coeffi
cient (
P
)
number that defi nes
the proportionality between a fl ux and a
concentration gradient and depends on the
properties of the membrane and the diffusing
molecule
permissiveness
the facilitation of the action of
one hormone by another; for example, the
effects of epinephrine are exacerbated by
thyroid hormone and by cortisol
peroxisome
(per-OX-ih-some) cell organelle that
destroys certain toxic products by oxidative
reactions
Peyer’s patches
lymphatic tissue located in
the lamina propria of the ileum of the small
intestine
pH
expression of a solution’s acidity; negative
logarithm to base 10 of H
+
concentration; pH
decreases as acidity increases
phagocyte
(FAH-go-site) any cell capable of
phagocytosis
phagocytosis
(fag-uh-sy-TOH-sis) engulfment of
particles by a cell
phagolysosome
an intracellular vesicle formed
when a lysosome and a phagosome combine;
the contents of the lysosome begin the process
of destroying the contents of the phagosome
phagosome
plasma membrane-bound,
intracellular sac formed when a phagocyte
engulfs a microbe
pharynx
(FAIR-inks) throat; passage common to
routes taken by food and air
phase shift
a resetting of the internal clock due to
altered environmental cues
phasic
(FAYZ-ik) intermittent;
compare
tonic
phenotype
(FEE-noh-type) gender based on
physical appearance
phosphate group
(FOS-fate) —PO
4
2–
phosphodiesterase
(fos-foh-dy-ES-ter-ase) enzyme
that catalyzes cyclic AMP breakdown to AMP
phospholipase A
2
(fos-fo-LY-pase A-two) enzyme
that splits arachidonic acid from plasma
membrane phospholipid
phospholipase C
receptor-controlled
plasma-membrane enzyme that catalyzes
phosphatidylinositol bisphosphate breakdown
to inositol trisphosphate and diacylglycerol
phospholipid
(fos-foh-LIP-id) lipid subclass
similar to triglyceride except that a phosphate
group (—PO
4
2–
) and small nitrogen-containing
molecule are attached to third hydroxyl
group of glycerol; major component of cell
membranes
phosphoprotein phosphatase
(FOS-fah-tase)
enzyme that removes phosphate from protein
phosphoric acid
(fos-FOR-ik) acid generated
during catabolism of phosphorus-containing
compounds; dissociates to form inorganic
phosphate and hydrogen ions
phosphorylation
(fos-for-ah-LAY-shun)
addition of phosphate group to an organic
molecule
photopigment
light-sensitive molecule altered
by absorption of photic energy of certain
wavelengths; consists of opsin bound to a
chromophore
photoreceptor
sensory cell specialized to respond
to light; contains pigments that make it
sensitive to different light wavelengths
phrenic nerves
main motor nerves innervating
the diaphragm and providing the impulses to
inspire
physiological dead space
sum of the anatomic
and alveolar dead spaces; it is the part of the
respiratory tree in which gas exchange with
blood does not occur
physiological genomics
application of the
understanding of how genes are regulated
to the study of physiology; the link between
genes and physiology
physiology
(fi z-ee-OL-uh-jee) branch of biology
dealing with the mechanisms by which living
organisms function
pia mater
(PEE-ah MAH-ter) innermost of three
membranes (meninges) covering the brain
pigment epithelium
dark, innermost layer
of the retina; absorbs light that bypasses
photopigments
pinocytosis
(pin-oh-sy-TOH-sis) endocytosis
when the vesicle encloses extracellular fl uid or
specifi c molecules in the extracellular fl uid that
have bound to proteins on the extracellular
surface of the plasma membrane
pitch
degree of how high or low a sound is
perceived
pituitary gland
(pih-TOO-ih-tar-ee) endocrine
gland that lies in bony pocket below
hypothalamus; constitutes anterior pituitary
and posterior pituitary
pituitary gonadotropin
see
gonadotropic hormone
placenta
(plah-SEN-tah) interlocking fetal
and maternal tissues that serve as organ of
molecular exchange between fetal and maternal
circulations
plasma
(PLAS-muh) liquid portion of blood;
component of extracellular fl uid
plasma cell
cell that differentiates from activated
B lymphocytes and secretes antibodies
plasma membrane
membrane that forms outer
surface of cell and separates cell’s contents
from extracellular fl uid
plasma membrane effector protein
plasma-
membrane protein that serves as ion channel or
enzyme in signal transduction sequence
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