G-14 Glossaryposterior portions. The anterior pituitary secretes
ACTH, TSH, FSH, LH, growth hormone, and
prolactin. The posterior pituitary releases oxytocin
and antidiuretic hormone (ADH), which are
produced by the hypothalamus.
plasma (plaz 9 m ̆a) The fluid portion of the blood.
Unlike serum (which lacks fibrinogen), plasma is
capable of forming insoluble fibrin threads when in
contact with test tubes.
plasma cells Cells derived from B lymphocytes
that produce and secrete large amounts of antibodies.
They are responsible for humoral immunity.
plasma membrane The selectively permeable
structure that regulates the transport of materials into
and out of the cell, and that separates the intracellular
from the extracellular compartment. Also called the
cell membrane.
platelet (pl ̄at 9 let) A disc-shaped structure, 2 to
4 micrometers in diameter, derived from bone
marrow cells called megakaryocytes. Platelets
circulate in the blood and participate (together with
fibrin) in forming blood clots.
pluripotent (ploo-rip 9 ̆o-tent) A term used
to describe the ability of early embryonic cells
to specialize to produce all tissues except the
trophoblast cells of the placenta.
pneumotaxic (noo 0 m ̆o-tak 9 sik) center A neural
center in the pons that rhythmically inhibits
inspiration in a manner independent of sensory input.
pneumothorax (noo 0 mo-thor 9 aks) An abnormal
condition in which air enters the intrapleural space,
either through an open chest wound or from a tear
in the lungs. This can lead to the collapse of a lung
(atelectasis).
PNS peripheral nervous system The nerves and
ganglia.
Poiseuille’s (pw ̆a-z ̄u 9 yez) law The statement that
the rate of blood flow through a vessel is directly
proportional to the pressure difference between the
two ends of the vessel and inversely proportional to
the length of the vessel, the viscosity of the blood,
and the fourth power of the radius of the vessel.
polar body A small daughter cell formed by
meiosis that degenerates in the process of oocyte
production.
polar molecule A molecule in which the shared
electrons are not evenly distributed, so that one side
of the molecule is negatively (or positively) charged
in comparison with the other side. Polar molecules
are soluble in polar solvents such as water.
polycythemia (pol 0 e-si-the 9 -me- ̆a) An abnormally
high red blood cell count.
polydipsia (pol 0 e-dip 9 se- ̆a) Excessive thirst.
polymer (pol 9 ̆ı-mer) A large molecule formed by
the combination of smaller subunits, or monomers.
polymorphonuclear (pol 0 e-mor 0 f ̆o-noo 9 kle-ar)
leukocyte A granular leukocyte containing a
nucleus with a number of lobes connected by thin
cytoplasmic strands. This term includes neutrophils,
eosinophils, and basophils.
polypeptide (pol 0 e-pep 9 t ̄ıd) A chain of amino acids
connected by covalent bonds called peptide bonds. A
very large polypeptide is called a protein.
polyphagia (pol 9 e-fa 0 je- ̆a) Excessive eating.
polysaccharide (pol 0 e-sak 9 ̆a-r ̄ıd) A carbohydrate
formed by covalent bonding of numerous
monosaccharides. Examples are glycogen and starch.
polyuria (pol 0 e-yoor 9 e- ̆a) Excretion of an
excessively large volume of urine in a given period.
portal (por 9 tal) system A system of vessels
consisting of two capillary beds in series, where
blood from the first is drained by veins into a
second capillary bed, which in turn is drained by
veins that return blood to the heart. The two majorproportional to the fourth power of the radius of the
vessel.
peristalsis (per 0 ̆ı-stal 9 sis) Waves of smooth
muscle contraction in smooth muscles of the tubular
digestive tract. It involves circular and longitudinal
muscle fibers at successive locations along the tract
and serves to propel the contents of the tract in one
direction.
permissive effect The phenomenon in which the
presence of one hormone “permits” the full exertion
of the effects of another hormone. This may be due
to promotion of the synthesis of the active form of
the second hormone, or it may be due to an increase
in the sensitivity of the target tissue to the effects of
the second hormone.
pH The symbol (short for potential of hydrogen)
used to describe the hydrogen ion (H^1 ) concentration
of a solution. The pH scale in common use ranges
from 0 to 14. Solutions with a pH of 7 are neutral;
those with a pH lower than 7 are acidic; and those
with a higher pH are basic.
phagocytosis (fag 0 ̆o-si-to 9 sis) Cellular eating; the
ability of some cells (such as white blood cells) to
engulf large particles (such as bacteria) and digest
these particles by merging the food vacuole in which
they are contained with a lysosome containing
digestive enzymes.
phenylalanine (fen 0 il-al 9 ̆a-n ̄en) An amino acid that
also serves as the precursor for L-dopa, dopamine,
norepinephrine, and epinephrine.
phenylketonuria (fen 0 il-k ̄et 0 n-oor 9 e- ̆a) (PKU)
An inborn error of metabolism that results in the
inability to convert the amino acid phenylalanine
into tyrosine. This defect can cause central nervous
system damage if the child is not placed on a diet low
in phenylalanine.
phonocardiogram (fo 0 n ̆o-kar 9 de- ̆o-gram) A visual
display of the heart sounds.
phosphatidylcholine (fos-fat 0 i-dil-ko 9 len) The
chemical name for the molecule also called lecithin.
phosphodiesterase (fos 0 fo-di-es 9 ter- ̆as) An
enzyme that cleaves cyclic AMP into inactive
products, thus inhibiting the action of cyclic AMP as
a second messenger.
phospholipid (fos 0 fo-lip 9 id) A lipid containing
a phosphate group. Phospholipid molecules (such
as lecithin) are polar on one end and nonpolar on
the other end. They make up a large part of the
cell membrane and function in the lung alveoli as
surfactants.
phosphorylation (fos 0 for- ̆ı-la 9 shun) The addition
of an inorganic phosphate group to an organic
molecule; for example, the addition of a phosphate
group to ADP to make ATP or the addition of a
phosphate group to specific proteins as a result of the
action of protein kinase enzymes.
photoreceptors (fo 0 to-re-sep 9 torz) Sensory cells
(rods and cones) that respond electrically to light.
They are located in the retina of the eyes.
pia mater (pi 9 ̆a ma 9 ter) The innermost of the
connective tissue meninges that envelops the brain
and spinal cord.
pineal (pin 9 e-al) gland A gland within the brain
that secretes the hormone melatonin. It is affected by
sensory input from the photoreceptors of the eyes.
pinocytosis (pin 0 ̆o-si-to 9 sis) Cell drinking;
invagination of the cell membrane to form narrow
channels that pinch off into vacuoles. This permits
cellular intake of extracellular fluid and dissolved
molecules.
pituitary (p ̆ı-too 9 ̆ı-ter-e) gland Also called the
hypophysis. A small endocrine gland joined to the
hypothalamus at the base of the brain. The pituitary
gland is functionally divided into anterior andto the total rate of plasma flow to the kidneys. PAH
is filtered and secreted by the renal nephrons but not
reabsorbed.
pancreatic (pan 0 kre-at 9 ik) islets Islands of
endocrine units within the more abundant exocrine
acini of the pancreas. Each pancreatic islet contains
beta cells that secrete inulin, alpha cells that secrete
glucagon, and delta cells that secrete somatostatin.
Also called islets of Langerhans.
pancreatic juice The secretions of the pancreas
that are transported by the pancreatic duct to the
duodenum. Pancreatic juice contains bicarbonate
and the digestive enzymes trypsin, lipase, and
amylase.
Paneth cells Located at the bottom of intestinal
crypts, Paneth cells secrete lysozyme and bactericidal
peptides called defensins.
paracrine (par 9 ̆a-krin) regulator A regulatory
molecule produced within one tissue that acts on a
different tissue of the same organ. For example, the
endothelium of blood vessels secretes a number of
paracrine regulators that act on the smooth muscle
layer of the vessels to cause vasoconstriction or
vasodilation.
parasympathetic (par 0 ̆a-sim 0 p ̆a-thet 9 ik) Pertaining
to the craniosacral division of the autonomic nervous
system.
parathyroid (par 0 ̆a-thi 9 roid) hormone (PTH) A
polypeptide hormone secreted by the parathyroid
glands. PTH acts to raise the blood Ca^21 levels
primarily by stimulating resorption of bone.
parietal (pah-ri 9 e-tal) cells Cells in the gastric
glands that secrete hydrochloric acid (HCl).
Parkinson’s disease A tremor of the resting
muscles and other symptoms caused by inadequate
dopamine-producing neurons in the basal nuclei of
the cerebrum. Also called paralysis agitans.
parturition (par 0 tyoo-rish 9 un) The process of
giving birth; childbirth.
passive immunity Specific immunity granted by
the administration of antibodies made by another
organism.
Pasteur effect A decrease in the rate of glucose
utilization and lactic acid production in tissues or
organisms by their exposure to oxygen.
pathogen (path 9 ̆o-jen) Any disease-producing
microorganism or substance.
pathogen recognition receptors Receptor proteins
on cells of the innate immune system that recognize
pathogen-associated molecular patterns (PAMPS).
One important group of pathogen recognition
receptors is the Toll-like receptors.
pepsin (pep 9 sin) The protein-digesting enzyme
secreted in gastric juice.
peptic ulcer (pep 9 tik ul 9 ser) An injury to the
mucosa of the esophagus, stomach, or small intestine
caused by the breakdown of gastric barriers to self-
digestion or by excessive amounts of gastric acid.
perfusion (per 9 fyoo 0 zhun) The flow of blood
through an organ.
perilymph (per 9 ̆ı-limf) The fluid that fills the space
between the membranous and bony labyrinths of the
inner ear.
perimysium (per 0 ̆ı-mis 9 e-um) The connective
tissue surrounding a fascicle of skeletal muscle
fibers.
periosteum (per 0 e-os 9 te-um) Connective tissue
covering bones. It contains osteoblasts, and is
therefore capable of forming new bone.
peripheral resistance The resistance to blood flow
through the arterial system. Peripheral resistance
is largely a function of the radius of small arteries
and arterioles. The resistance to blood flow isfox36375_glo_G1-G19.indd 14fox36375_glo_G1-G19.indd 14 2/4/15 12:29 PM2/4/15 12:29 PM