pacemaker cells: Cells of the sinoatrial node that set the pace of cardiac contraction.
Pacinian corpuscle: A receptor sensitive to vibration.
palate: The horizontal partition separating the oral cavity from the nasal cavity and nasopharynx; divided into an anterior bony (hard) palate and a posterior fleshy (soft) palate.
palatine: Pertaining to the palate.
palpate: To examine by touch.
palpebrae: Eyelids.
pancreas: A digestive organ containing exocrine and endocrine tissues; the exocrine portion secretes pancreatic juice, and the endocrine portion secretes hormones, including insulin and glucagon.
pancreatic duct: A tubular duct that carries pancreatic juice from the pancreas to the duodenum.
pancreatic islets: Aggregations of endocrine cells in the pancreas; also called islets of Langerhans.
pancreatic juice: A mixture of buffers and digestive enzymes that is discharged into the duodenum under the stimulation of the enzymes secretin and cholecystokinin.
pancreatitis: An inflammation of the pancreas.
Papanicolaou (Pap) test: A test for the detection of malignancies based on the cytological appearance of epithelial cells, especially those of the cervix and uterus.
papilla: A small, conical projection.
paralysis: The loss of voluntary motor control over a portion of the body.
paranasal sinuses: Bony chambers, lined by respiratory epithelium, that open into the nasal cavity; the frontal, ethmoidal, sphenoidal, and maxillary sinuses.
parasagittal: A section or plane that parallels the midsagittal plane but that does not pass along the midline.
parasympathetic division: One of the two divisions of the autonomic nervous system; also called craniosacral division; generally responsible for activities that conserve energy and lower the metabolic rate.
parasympathomimetic drugs: Drugs that mimic the actions of parasympathetic stimulation.
parathyroid glands: Four small glands embedded in the posterior surface of the thyroid gland; secrete parathyroid hormone.
parathyroid hormone (PTH): A hormone secreted by the parathyroid glands when plasma calcium levels fall below the normal range; causes increased osteoclast activity, increased intestinal calcium uptake, and decreased calcium ion loss at the kidneys.
parenchyma: The cells of a tissue or organ that are responsible for fulfilling its functional role; distinguished from the stroma of that tissue or organ.
paresthesia: A sensory abnormality that produces a tingling sensation.
parietal: Referring to the body wall or outer layer.
parietal cells: Cells of the gastric glands that secrete hydrochloric acid and intrinsic factor.
Parkinson's disease: A progressive motor disorder caused by the degeneration of cerebral nuclei.
parotid salivary glands: Large salivary glands that secrete a saliva containing high concentrations of salivary (alpha) amylase.
pars distalis: The large, anterior portion of the anterior pituitary gland.
pars intermedia: The portion of the anterior pituitary that is immediately adjacent to the posterior pituitary and the infundibulum.
pars nervosa: The posterior pituitary gland.
pars tuberalis: The portion of the anterior pituitary that wraps around the infundibulum superior to the posterior pituitary.
parturition: Childbirth, delivery.
patella: The sesamoid bone of the kneecap.
pathogen: A disease-causing organism.
pathogenic: Disease-causing.
pathologist: An M.D. specializing in the identification of diseases on the basis of characteristic structural and functional changes in tissues and organs.
pedicel: A slender process of a podocyte that forms part of the filtration apparatus of the kidney glomerulus.
pedicles: Thick, bony struts that connect the vertebral body with the articular and spinous processes.
pelvic cavity: The inferior subdivision of the abdominopelvic (peritoneal) cavity; encloses the urinary bladder, the sigmoid colon and rectum, and male or female reproductive organs.
pelvis: A bony complex created by the articulations among the coxae, the sacrum, and the coccyx.
penis: A component of the male external genitalia; a copulatory organ that surrounds the urethra and serves to introduce semen into the female vagina; the developmental equivalent of the female clitoris.
pepsin: A proteolytic enzyme secreted by the chief cells of the gastric glands in the stomach.
peptidases: Enzymes that split peptide bonds and release amino acids.
peptide: A chain of amino acids linked by peptide bonds.
peptide bond: A covalent bond between the amino group of one amino acid and the carboxyl group of another.
perforating canal: A passageway in compact bone that is at right angles to the axes of the osteons, between the periosteum and endosteum.
perfusion: The blood flow through a tissue.
pericardial cavity: The space between the parietal pericardium and the epicardium (visceral pericardium) that covers the outer surface of the heart.
pericarditis: An inflammation of the pericardium.
pericardium: The fibrous sac that surrounds the heart; its inner, serous lining is continuous with the epicardium.
perichondrium: The layer that surrounds a cartilage, consisting of an outer fibrous region and an inner cellular region.
perikaryon: The cytoplasm that surrounds the nucleus in the cell body of a neuron.
perilymph: A fluid similar in composition to cerebrospinal fluid; located in the spaces between the bony labyrinth and the membranous labyrinth of the inner ear.
perimysium: A connective tissue partition that separates adjacent fasciculi in a skeletal muscle.
perineum: The pelvic floor and its associated structures.
perineurium: A connective tissue partition that separates adjacent bundles of nerve fibers in a peripheral nerve.
periodontal ligament: Collagen fibers that bind the cementum of a tooth to the periosteum of the surrounding alveolus.
periosteum: The layer that surrounds a bone, consisting of an outer fibrous region and inner cellular region.
peripheral nervous system (PNS): All neural tissue outside the central nervous system.
peripheral resistance: The resistance to blood flow; primarily caused by friction with the vascular walls.
peristalsis: A wave of smooth muscle contractions that propels materials along the axis of a tube such as the digestive tract, the ureters, or the ductus deferens.
peritoneal cavity: See abdominopelvic cavity.
peritoneum: The serous membrane that lines the peritoneal (abdominopelvic) cavity.
peritonitis: An inflammation of the peritoneum.
peritubular capillaries: A network of capillaries that surrounds the proximal and distal convoluted tubules of the kidneys.
permeability: The ease with which dissolved materials can cross a membrane; if the membrane is freely permeable, any molecule can cross it; if impermeable, nothing can cross; most biological membranes are selectively permeable.
peroxisome: A membranous vesicle containing enzymes that break down hydrogen peroxide (H2O2).
pes: The foot.
petrosal ganglion: A sensory ganglion of the glossopharyngeal nerve (N IX).
petrous: Stony; usually refers to the thickened portion of the temporal bone that encloses the inner ear.
pH: The negative exponent of the hydrogen ion concentration, expressed in moles per liter.
phagocyte: A cell that performs phagocytosis.
phagocytosis: The engulfing of extracellular materials or pathogens; the movement of extracellular materials into the cytoplasm by enclosure in a membranous vesicle.
phalanx/phalanges: Bones of the fingers or toes.
pharmacology: The study of drugs, their physiological effects, and their clinical uses.
pharynx: The throat; a muscular passageway shared by the digestive and respiratory tracts.
phasic response: A pattern of response to stimulation by sensory neurons that are normally inactive; stimulation causes a burst of neural activity that ends when the stimulus either stops or stops changing in intensity.
phenotype: Physical characteristics that are genetically determined.
phonation: Sound production at the larynx.
phosphate group: PO43-; a functional group that can be attached to an organic molecule; required for the formation of high-energy bonds.
phospholipid: An important membrane lipid whose structure includes both hydrophilic and hydrophobic regions.
phosphorylation: The addition of a high-energy phosphate group to a molecule.
photoreception: Sensitivity to light.
physiology: The study of function; deals with the ways organisms perform vital activities.
pia mater: The tough, outer meningeal layer that surrounds the central nervous system.
pigment: A compound with a characteristic color.
pineal gland: Neural tissue in the posterior portion of the roof of the diencephalon; secretes melatonin.
pinocytosis: The introduction of fluids into the cytoplasm by enclosing them in membranous vesicles at the cell surface.
pituitary gland: An endocrine organ that is situated in the sella turcica of the sphenoid bone and is connected to the hypothalamus by the infundibulum; includes the posterior pituitary (pars nervosa) and the anterior pituitary (pars intermedia and pars distalis).
placenta: A temporary structure in the uterine wall that permits diffusion between the fetal and maternal circulatory systems; see afterbirth.
plantar: Referring to the sole of the foot.
plasma: The fluid ground substance of whole blood; what remains after the cells have been removed from a sample of whole blood.
plasma cell: An activated B cell that secretes antibodies.
plasmalemma: A cell membrane.
platelets: Small packets of cytoplasm that contain enzymes important in the clotting response; manufactured in bone marrow by megakaryocytes.
pleura: The serous membrane that lines the pleural cavities.
pleural cavities: Subdivisions of the thoracic cavity that contain the lungs.
pleuritis: An inflammation of the pleura; also called pleurisy.
plexus: A network or braid.
plica: A permanent transverse fold in the wall of the small intestine.
pneumotaxic center: A center in the reticular formation of the pons that regulates the activities of the apneustic and respiratory rhythmicity centers to adjust the pace of respiration.
pneumothorax: The introduction of air into the pleural cavity.
podocyte: A cell whose processes surround the kidney glomerular capillaries and assist in filtration.
polar body: A nonfunctional packet of cytoplasm that contains chromosomes eliminated from an oocyte during meiosis.
polar bond: A covalent bond in which electrons are shared unequally.
polarized: Referring to cells that have regional differences in organelle distribution or cytoplasmic composition along a specific axis, such as between the basement membrane and free surface of an epithelial cell.
pollex: The thumb.
polymer: A large molecule consisting of a long chain of subunits.
polymorph: A polymorphonuclear leukocyte; a neutrophil.
polypeptide: A chain of amino acids strung together by peptide bonds; those containing more than 100 peptides are called proteins.
polyribosome: Several ribosomes linked by their translation of a single mRNA strand.
polysaccharide: A complex sugar, such as glycogen or a starch.
polysynaptic reflex: A reflex in which interneurons are interposed between the sensory fiber and the motor neuron(s).
polyunsaturated fats: Fatty acids containing carbon atoms that are linked by double bonds.
polyuria: Excessive urine production.
pons: The portion of the metencephalon that is anterior to the cerebellum.
popliteal: Pertaining to the back of the knee.
porphyrins: Ring-shaped molecules that form the basis of important respiratory and metabolic pigments, including heme and the cytochromes.
porta hepatis: A region of mesentery between the duodenum and liver that contains the hepatic artery proper, the hepatic portal vein, and the common bile duct; also called hilus.
positive feedback: A mechanism that increases a deviation from normal limits after an initial stimulus.
postabsorptive state: A period that begins 4 hours after a meal; characterized by falling blood glucose concentrations and the mobilization of metabolic reserves.
postcentral gyrus: The primary sensory cortex, where touch, vibration, pain, temperature, and taste sensations arrive and are consciously perceived.
posterior: Toward the back; dorsal.
postganglionic neuron: An autonomic neuron in a peripheral ganglion, whose activities control peripheral effectors.
postovulatory phase: The secretory phase of the menstrual cycle.
postsynaptic membrane: The portion of the cell membrane of a postsynaptic cell that is part of a synapse.
potential difference: The separation of opposite charges; requires a barrier that prevents ion migration.
precentral gyrus: The primary motor cortex of a cerebral hemisphere, located anterior to the central sulcus.
prefrontal cortex: The anterior portion of each cerebral hemisphere; thought to be involved with higher intellectual functions, predictions, calculations, and so forth.
preganglionic neuron: A visceral motor neuron in the central nervous system whose output controls one or more ganglionic motor neurons in the peripheral nervous system.
premolars: Bicuspids; teeth with flattened occlusal surfaces; located anterior to the molar teeth.
premotor cortex: The motor association area between the precentral gyrus and the prefrontal area.
preoptic nucleus: The hypothalamic nucleus that coordinates thermoregulatory activities.
prepuce: The loose fold of skin that surrounds the glans penis (in males) or the clitoris (in females).
preputial glands: Glands on the inner surface of the prepuce that produce a viscous, odorous secretion called smegma.
presbyopia: Farsightedness; an inability to accommodate for near vision.
presynaptic membrane: The synaptic surface where neurotransmitter release occurs.
prevertebral ganglion: See collateral ganglion.
prime mover: A muscle that performs a specific action.
proenzyme: An inactive enzyme secreted by an epithelial cell.
progesterone: The most important progestin secreted by the corpus luteum after ovulation.
progestins: Steroid hormones structurally related to cholesterol; progesterone is an example.
prognosis: A prediction about the possibility or time course of recovery from a specific disease.
projection fibers: Axons carrying information from the thalamus to the cerebral cortex.
prolactin: The hormone that stimulates functional development of the mammary gland in females; a secretion of the anterior pituitary gland.
prolapse: The abnormal descent or protrusion of a portion of an organ, such as the vagina or anorectal canal.
proliferative phase: A portion of the uterine cycle; the interval of estrogen-induced repair of the functional zone of the endometrium through the growth and proliferation of epithelial cells in the uterine glands.
pronation: The rotation of the forearm that makes the palm face posteriorly.
prone: Lying face down with the palms facing the floor.
pronucleus: An enlarged ovum or spermatozoon nucleus that forms after fertilization but before amphimixis.
properdin: The complement factor that prolongs and enhances non-antibody-dependent complement binding to bacterial cell walls.
prophase: The initial phase of mitosis; characterized by the appearance of chromosomes, the breakdown of the nuclear membrane, and the formation of the spindle apparatus.
proprioception: The awareness of the positions of bones, joints, and muscles.
prostaglandin: A fatty acid secreted by one cell that alters the metabolic activities or sensitivities of adjacent cells; also called local hormone.
prostatectomy: The surgical removal of the prostate gland.
prostate gland: An accessory gland of the male reproductive tract, contributing roughly one-third of the volume of semen.
prostatitis: An inflammation of the prostate gland.
prosthesis: An artificial substitute for a body part.
protease: See proteinase.
protein: A large polypeptide with a complex structure; examples include enzymes and structural proteins.
proteinase: An enzyme that breaks down proteins into peptides and amino acids.
proteinuria: Abnormal amounts of protein in urine.
proteoglycan: A compound containing a large polysaccharide complex attached to a relatively small protein; examples include hyaluronan and chondroitin sulfate.
prothrombin: A circulating proenzyme of the common pathway of the clotting system; converted to thrombin by the enzyme thromboplastin.
proton: A fundamental particle bearing a positive charge.
protraction: Movement anteriorly in the horizontal plane.
proximal: Toward the attached base of an organ or structure.
proximal convoluted tubule (PCT): The portion of the nephron that is situated between Bowman’s capsule and the loop of Henle; the major site of active reabsorption from filtrate.
pruritis: Itching.
pseudopodia: Temporary cytoplasmic extensions typical of mobile or phagocytic cells.
pseudostratified epithelium: An epithelium that contains several layers of nuclei but whose cells are all in contact with the underlying basement membrane.
psoriasis: A skin condition characterized by excessive keratin production and the formation of dry, scaly patches on the body surface.
psychosomatic condition: An abnormal physiological state with a psychological origin.
puberty: A period of rapid growth, sexual maturation, and the appearance of secondary sexual characteristics; normally occurs at ages 10–15 years.
pubic symphysis: The fibrocartilaginous amphiarthrosis between the pubic bones of the ossa coxae.
pubis: The anterior, inferior component of the os coxae.
pudendum: The external genitalia.
pulmonary circuit: Blood vessels between the pulmonary semilunar valve of the right ventricle and the entrance to the left atrium; the blood flow through the lungs.
pulmonary ventilation: The movement of air into and out of the lungs.
pulp cavity: The internal chamber in a tooth, containing blood vessels, lymphatic vessels, nerves, and the cells that maintain the dentin.
pulpitis: An inflammation of the tissues of the pulp cavity.
pupil: The opening in the center of the iris through which light enters the eye.
purine: A nitrogen compound with a double ring-shaped structure; examples include adenine and guanine, two nitrogenous bases that are common in nucleic acids.
Purkinje cell: A large, branching neuron of the cerebellar cortex.
Purkinje fibers: Specialized conducting cardiocytes in the ventricles of the heart.
pus: An accumulation of debris, fluid, dead and dying cells, and necrotic tissue.
putamen: The thalamic nucleus involved in the integration of sensory information prior to projection to the cerebral hemispheres.
P wave: A deflection of the ECG corresponding to atrial depolarization.
pyelogram: A radiographic image of the kidneys and ureters.
pyelonephritis: An inflammation of the kidneys.
pyloric sphincter: A sphincter of smooth muscle that regulates the passage of chyme from the stomach to the duodenum.
pylorus: The gastric region between the body of the stomach and the duodenum; includes the pyloric sphincter.
pyrexia: A fever.
pyrimidine: A nitrogen compound with a single ring-shaped structure; examples include cytosine, thymine, and uracil, nitrogenous bases that are common in nucleic acids.
pyrogen: A compound that promotes a fever.
pyruvic acid: A three-carbon compound produced by glycolysis.