Percussion (per-KUSH-un) The act of striking (percussing) an underly-
ing part of the body with short, sharp blows as an aid in diagnos-
ing the part by the quality of the sound produced.
Perforating canal (PER-fo-ra'-ting) A minute passageway by means of
which blood vessels and nerves from the periosteum penetrate
into compact bone. Also called volkmann’s canal (FOLK-manz).
Pericardial cavity (per'-i-KAR-de-al) Small potential space between
the visceral and parietal layers of the serous pericardium that
contains pericardial fluid.
Pericardium (per'-i-KAR-de-um) A loose-fitting membrane that
encloses the heart, consisting of a superficial fibrous layer and a
deep serous layer.
Perichondrium (per'-i-KON-dre-um) The membrane that covers
Perilymph (PER-i-limf) The fluid contained between the bony and
membranous labyrinths of the inner ear.
Perineum (per'-i-NE-um) The pelvic floor; the space between the
anus and the scrotum in the male and between the anus and the
vulva in the female.
Periodontal disease (per-e-o-DON-tal) A collective term for condi-
tions characterized by degeneration of gingivae, alveolar bone,
periodontal ligament, and cementum.
Periodontal ligament The periosteum lining the alveoli (sockets) for
the teeth in the alveolar processes of the mandible and maxillae.
Periosteum (per'-e-OS-te-um) The membrane that covers bone and
consists of connective tissue, osteogenic cells, and osteoblasts;
is essential for bone growth, repair, and nutrition.
Peripheral (pe-RIF-er-al) Located on the outer part or a surface of the
Peripheral nervous system (PNS) The part of the nervous system that
lies outside the central nervous system, consisting of nerves and
Peristalsis (per'-i-STAL-sis) Successive muscular contractions along
the wall of a hollow muscular structure.
Peritoneum (per'-i-to-NE-um) The largest serous membrane of the
body that lines the abdominal cavity and covers the viscera within
Peritonitis (per'-i-to-NT-tis) Inflammation of the peritoneum.
Peroxisome (per-OK-si-som) Organelle similar in structure to a
lysosome that contains enzymes that use molecular oxygen to
oxidize various organic compounds; such reactions produce
hydrogen peroxide; abundant in liver cells.
Perspiration Sweat; produced by sudoriferous (sweat) glands and
containing water, salts, urea, uric acid, amino acids, ammonia,
sugar, lactic acid, and ascorbic acid. Helps maintain body tem-
perature and eliminate wastes.
pH A measure of the concentration of hydrogen ions (H+) in a solu-
tion. The pH scale extends from 0 to 14, with a value of 7 express-
ing neutrality, values lower than 7 expressing increasing acidity,
and values higher than 7 expressing increasing alkalinity.
Phagocytosis (fag'-o-sT-TO-sis) The process by which phagocytes
ingest particulate matter; the ingestion and destruction of
microbes, cell debris, and other foreign matter.
Phalanx (FA-lanks) The bone of a finger or toe.
P lu r a l
Pharmacology (far'-ma-KOL-o-je) The science that deals with the
effects and uses of drugs in the treatment of disease.
Pharynx (FAR-inks) The throat; a tube that starts at the internal
nares and runs partway down the neck, where it opens into the
esophagus posteriorly and the larynx anteriorly.
Phenotype (FE-no-tTp) The observable expression of genotype;
physical characteristics of an organism determined by genetic
makeup and influenced by interaction between genes and inter-
nal and external environmental factors.
Phlebitis (fle-BT-tis) Inflammation of a vein, usually in a lower limb.
Photopigment A substance that can absorb light and undergo struc-
tural changes that can lead to the development of a receptor poten-
tial. An example is rhodopsin. In the eye, also called visual pigment.
Photoreceptor Receptor that detects light shining on the retina of
Physiology (fiz'-e-OL-o-je) Science that deals with the functions of an
organism or its parts.
Pia mater (PT-a MA-ter
PE-a MA-ter) The innermost of the three
meninges (coverings) of the brain and spinal cord.
Pineal gland (PTN-e-al) A cone-shaped gland located in the roof of
the third ventricle that secretes melatonin.
Pinna (PIN-na) The projecting part of the external ear composed of
elastic cartilage and covered by skin and shaped like the flared
end of a trumpet. Also called the auricle (AW-ri-kul).
Pituitary gland (pi-TOO-i-tar-e) A small endocrine gland occupying
the hypophyseal fossa of the sphenoid bone and attached to the
hypothalamus by the infundibulum. Also called the hypophysis
Pivot joint A synovial joint in which a rounded, pointed, or conical sur-
face of one bone articulates with a ring formed partly by another
bone and partly by a ligament, as in the joint between the atlas and
axis and between the proximal ends of the radius and ulna.
Placenta (pla-SEN-ta) The special structure through which the
exchange of materials between fetal and maternal circulations
occurs. Also called the afterbirth.
Plantar flexion (PLAN-tar FLEK-shun) Bending the foot in the direc-
tion of the plantar surface (sole).
Plaque (PLAK) A layer of dense proteins on the inside of a plasma
membrane in adherens junctions and desmosomes. A mass of
bacterial cells, dextran (polysaccharide), and other debris that
adheres to teeth (dental plaque). See also atherosclerotic plaque.
Plasma (PLAZ-ma) The extracellular fluid found in blood vessels;
blood minus the formed elements.
Plasma cell Cell that develops from a B cell (lymphocyte) and pro-
Plasma (cell) membrane Outer, limiting membrane that separates
the cell's internal parts from extracellular fluid or the external
Platelet (PLAT-let) A fragment of cytoplasm enclosed in a cell mem-
brane and lacking a nucleus; found in the circulating blood; plays
a role in hemostasis. Also called a thrombocyte (THROM-bo-sTt).