Glossary 577vessels. Plasma is 52%–62% of the total blood (Chap-
ter 2).
Plasma cell(PLAZ-mah SELL) A cell derived from an acti-
vated B cell that produces antibodies to a specific antigen
(Chapter 14).
Plasma proteins(PLAZ-mah PRO-teenz) The proteins
that circulate in the liquid portion of the blood; include
albumin, globulins, and clotting factors (Chapter 11).
Plasticity(pla-STIS-si-tee) The ability of a tissue to grow
or change; used especially for the ability of the brain to
adapt to changing needs and to recruit different neurons
for certain functions, as may occur in recovery from a
stroke (Chapter 8).
Platelets(PLAYT-lets) Blood cells that are fragments of
larger cells (megakaryocytes) of the red bone marrow;
involved in blood clotting and other mechanisms of
hemostasis (Syn.—thrombocytes) (Chapter 4).
Pleural membranes (PLOOR-uhl MEM-braynz) The
serous membranes of the thoracic cavity (Chapter 1).
Plica circulares(PLEE-ka SIR-kew-LAR-es) The circular
folds of the mucosa and submucosa of the small intestine;
increase the surface area for absorption (Chapter 16).
Pneumonia(new-MOH-nee-ah) Inflammation of the lungs
caused by bacteria, viruses, or chemicals (Chapter 15).
Pneumotaxic center(NEW-moh-TAK-sik SEN-ter) The
respiratory center in the pons that helps bring about
exhalation (Chapter 15).
Pneumothorax(NEW-moh-THAW-raks) The accumula-
tion of air in the potential pleural space, which increases
intrapleural pressure and causes collapse of a lung
(Chapter 15).
Podocytes(POH-doh-sights) The cells that form the inner
layer of Bowman’s capsule of the renal corpuscle; adja-
cent foot processes form pores that make the layer very
permeable (Chapter 18).
Polarization(POH-lahr-i-ZAY-shun) The distribution of
ions on either side of a membrane; in a resting neuron or
muscle cell, sodium ions are more abundant outside the
cell, and potassium and negative ions are more abundant
inside the cell, giving the membrane a positive charge
outside and a relative negative charge inside (Chapter 7).
Polypeptide(PAH-lee-PEP-tyde) A short chain of amino
acids, not yet a specific protein (Chapter 2).
Polysaccharide (PAH-lee-SAK-ah-ryde) A carbohydrate
molecule that consists of many monosaccharides (usually
glucose) bonded together; includes glycogen, starch, and
cellulose (Chapter 2).
Polyuria(PAH-li-YOO-ree-ah) Increased urine formation
and output (Chapter 18).
Pons(PONZ) The part of the brain anterior and superior
to the medulla; contributes to the regulation of respira-
tion (from the Latin “bridge”) (Chapter 8).
Pore(POR) An opening on a surface to permit the passage
of materials (Chapter 3).Portal of entry(POR-tuhl of EN-tree) The way a
pathogen enters the body, such as natural body openings
or breaks in the skin (Chapter 22).
Portal of exit(POR-tuhl of EG-zit) The way a pathogen
leaves a host, such as in respiratory droplets, feces, or
reproductive secretions (Chapter 22).
Positive feedback(PAHS-ah-tiv FEED-bak) A control
system that requires an external event to stop or reverse
the stimulus; may become a self-perpetuating cycle that
causes harm (Chapter 1).
Positron emission tomography (PET)(PAHS-i-tron eh-
MISH-shun toh-MAH-grah-fee) An imaging technique
that depicts rate of metabolism or blood flow in organs or
tissues (Chapter 1).
Posterior(poh-STEER-ee-your) Toward the back (Syn.—
dorsal) (Chapter 1).
Postganglionic neuron(POST-gang-lee-ON-ik) In the
autonomic nervous system, a neuron that extends from a
ganglion to a visceral effector (Chapter 8).
Precapillary sphincter(pree-KAP-i-lar-ee SFINK-ter) A
smooth muscle cell at the beginning of a capillary net-
work that regulates the flow of blood through the net-
work (Chapter 13).
Preganglionic neuron(PRE-gang-lee-ON-ik) In the auto-
nomic nervous system, a neuron that extends from the
CNS to a ganglion and synapses with a postganglionic
neuron (Chapter 8).
Premotor area(pre-MOH-ter) The area of the frontal
cerebral cortex anterior to the motor area; is concerned
with learning sequential movements (Chapter 8).
Presbyopia(PREZ-bee-OH-pee-ah) Farsightedness that is
a consequence of aging and the loss of elasticity of the
lens (Chapter 9).
Pressoreceptors(PRESS-oh-ree-SEP-ters) The sensory
receptors in the carotid sinuses and aortic sinus that
detect changes in blood pressure (Chapter 9).
Primary bronchi(PRY-ma-ree BRONG-kye) The two
branches of the lower end of the trachea; air passageways
to the right and left lungs (Chapter 15).
Prime mover(PRYME MOO-ver) The muscle responsible
for the main action when a joint is moved (Chapter 7).
Prions(PREE-ons) Proteinaceous infectious particles that
are the cause of lethal disease of the nervous system in
people and animals (Chapter 2).
Process(PRAH-sess) 1. An action or series of actions that
has a predictable and specific outcome, such as the
process of protein synthesis. 2. A cellular extension, such
as the axon of a neuron. 3. A projection of a bone, often
for muscle attachment, such as the spinous process of a
vertebra (Chapter 1).
Progesterone (proh-JESS-tuh-rohn) The sex hormone
secreted by the corpus luteum of the ovary and by the
placenta; contributes to the growth of the endometrium
and the maintenance of pregnancy (Chapter 10).30Scanlon(p3) Glossary 8/17/06 11:08 AM Page 577