598 Introduction to Anatomy and Physiology
pia mater (PIGH-ah MAY-ter) the delicate, innermost
membrane of the brain, which attaches directly to the
surface of the brain and the spinal cord
pineal gland (PI-nee-al) a pinecone-shaped gland in the
brain that releases the sleep-inducing hormone melatonin
pinna see auricle
pituitary gland (pi-TOO-i-tair-ee) a pea-sized gland
that activates a metabolic response in target tissues or
stimulates other endocrine glands to release hormones
pivot joint type of diarthrosis that permits rotation around
only one axis
placenta the organ that grows in the uterus to meet the
nutritional needs of the embryo and fetus
plantar fl exion downward motion of the foot away from
the lower leg
plantar warts warts that develop on the soles of the foot,
grow inward, and can become painful
plaque a sticky mixture of bacteria, food particles, and
mucus
plasma the liquid component of blood
plasma cells activated B lymphocytes that produce
antibodies, which circulate as free proteins in the blood
plasma membrane the membrane that defi nes the outer
shell of a cell
plastic a response characterized by some amount of
permanent deformation
platelet plug gathering of platelets that forms a small
mass at the site of an injury
platelets part of the formed elements of the blood; play a
vital role in blood clotting
pleura (PLOO-ra) the membrane that encases the lungs
pleural sac the thin, double-walled serous membrane
that surrounds the lungs
pleurisy (PLOOR-i-see) infl ammation of the pleura, the
membrane that encases the lungs
plexuses complex interconnections of nerves
pneumonia (noo-MOH-nee-ah) an infection of the lungs
that causes infl ammation; caused by a virus, bacterium,
fungus, or—in rare cases—parasites
podocytes (PAHD-oh-sights) “foot cells” that wrap around
capillaries in the glomerular capsule
polarized a condition that occurs when the inside of a cell
membrane is more negatively charged than the outside
polycythemia (PAHL-ee-sigh-THEE-mee-a) a condition
in which the bone marrow manufactures too many
red blood cells; caused by prolonged altitude exposure
and a genetic mutation
polydipsia (pahl-i-DIP-see-a) excessive thirst to
replenish water lost through polyuria
polymer a molecule made of many similar subunits
polypeptide a long chain of amino acids
polyphagia (pahl-ee-FAY-jee-a) increased hunger to
replace fats and proteins used as fuel sources
polyspermy fertilization of an oocyte by more than one
sperm
polyuria (pahl-ee-YOOR-ee-a) excessive urination to
eliminate glucose from the body
polyunsaturated fats one category of unsaturated fatty
acids; sources include corn oil and soybean oil
pons (pahnz) the section of the brain that plays a role in
regulating breathing
pores of Kohn (kohn) small openings in the alveolar
walls that allow gases and macrophages to travel
between the alveoli
positive feedback mechanism that further increases a
condition that has exceeded the normal homeostatic range
posterior (dorsal) body cavity continuous internal
opening located near the back of the body that includes
the cranial and spinal cavities
posterior pituitary one lobe of the pituitary gland that
stores two hormones produced by the hypothalamus:
antidiuretic hormone and oxytocin
postganglionic neuron (POHST-gayng-glee-AHN-ik) the
second neuron in a series that transmits impulses from
the CNS
precapillary sphincter (pree-KAP-i-LAIR-ee SFINGK-ter)
a band of smooth muscle fi bers that encircles the
capillaries at the arteriole-capillary junctions and controls
blood fl ow to the tissues
precipitation the formation of an insoluble complex,
such as a clump of antigen molecules joined together by
antibodies
preganglionic neuron (PREE-gayng-glee-AHN-ik) the fi rst
neuron in a series that transmits impulses from the CNS
premature atrial contractions (PACs) condition in which
an irritable piece of atrial heart tissue fi res before the
SA node causing the atria to contract too soon
premature ventricular contractions (PVCs) condition
in which Purkinje fi bers fi re before the SA node, causing
the ventricles to contract prematurely
prepuce (PREE-pyoos) the foreskin of the penis
presbycusis (PREHZ-bee-KYOO-sis) age-related
hearing loss
presbyopia (PREZ-bee-OH-pee-a) an age-related
version of farsightedness
pressure force distributed over a given area
pressure ulcers see decubitus ulcers
primary bronchi (BRAHNG-kigh) the two passageways
that branch off the trachea and lead to the right and left
lungs
primary follicle an ovarian follicle in which the primary
oocyte develops
primary immune response the initial immune system
response to a foreign invader such as a virus or bacterium
primary motor cortex outer region of the brain in the
frontal lobes that sends neural impulses to the skeletal
muscles
primary somatic sensory cortex outer region of
the brain in the parietal lobes that interprets sensory
impulses received from the skin, internal organs,
muscles, and joints
primary spinal curves those spinal curves present at
birth, including the thoracic and sacral curves
primordial follicle the structure that is formed when the
primary oocyte is surrounded by a single layer of follicle
cells in the ovarian follicle
progesterone (proh-JES-teh-rohn) a hormone produced
by the ovaries in women to help regulate the menstrual
cycle and promote breast development in puberty
prolactin a trophic hormone that stimulates the growth
of mammary glands and milk production in a nursing
mother
prolactin-releasing factor a hormone that triggers the
release of prolactin, which stimulates the secretory cells
of the mammary glands to produce milk
proliferative phase the phase of the uterine cycle during
which the functional layer of the endometrium grows
back after having been shed in the menstrual phase
pronation medial rotation of the forearm (palm down)
prophase the fi rst stage of cell division, during which the
chromosomes become visible and the nuclear membrane
disintegrates