Ovum (O-vum) The female reproductive or germ cell; an egg cell;
arises through completion of meiosis in a secondary oocyte after
penetration by a sperm.
Oxidation (ok-si-DA-shun) The removal of electrons from a molecule
or, less commonly, the addition of oxygen to a molecule that
results in a decrease in the energy content of the molecule. The
oxidation of glucose in the body is called cellular respiration.
Oxyhemoglobin (Hb-O2) (ok'-se-HE-mo-glo-bin) Hemoglobin com-
bined with oxygen.
Oxytocin (OT) (ok'-se-TO-sin) A hormone secreted by neurosecretory
cells in the hypothalamus that stimulates contraction of smooth
muscle in the pregnant uterus and myoepithelial cells around the
ducts of mammary glands.
P wave The deflection wave of an electrocardiogram that signifies
Pacinian corpuscle (pa-SIN-e-an) Oval-shaped pressure receptor
located in the dermis or subcutaneous tissue and consisting of
concentric layers of connective tissue wrapped around the den-
drites of a sensory neuron. Also called a lamellated corpuscle.
Palate (PAL-at) The horizontal structure separating the oral and the
nasal cavities; the roof of the mouth.
Palpate (PAL-pat) To examine by touch; to feel.
Pancreas (PAN-kre-as) A soft, oblong organ lying along the greater
curvature of the stomach and connected by a duct to the duode-
num. It is both an exocrine gland (secreting pancreatic juice) and
an endocrine gland (secreting insulin and glucagon).
Pancreatic duct (pan'-kre-AT-ik) A single large tube that unites with
the common bile duct from the liver and gallbladder and drains
pancreatic juice into the duodenum.
Pancreatic islet (T-let) A cluster of endocrine gland cells in the pan-
creas that secretes insulin, glucagon, somatostatin, and pancreatic
polypeptide. Also called an islet of Langerhans (LANG-er-hanz).
Papanicolaou test (pap'-a-NIK-o-la-oo) A cytological staining test
for the detection and diagnosis of premalignant and malignant
conditions of the female genital tract. Cells scraped from the epi-
thelium of the cervix of the uterus are examined microscopically.
Also called a Pap test or Pap smear.
Papilla (pa-PIL-a) A small nipple-shaped projection or elevation.
Paralysis (pa-RAL-a-sis) Loss or impairment of motor function due to
a lesion of nervous or muscular origin.
Paranasal sinus (par'-a-NA-zal SI-nus) A mucus-lined air cavity in a
skull bone that communicates with the nasal cavity. Paranasal
sinuses are located in the frontal, maxillary, ethmoid, and sphe-
Paraplegia (par-a-PLE-je-a) Paralysis of both lower limbs.
Parasagittal plane (par-a-SAJ-i-tal) A vertical plane that does not
pass through the midline and that divides the body or organs into
u n e q u a l
left and right portions.
Parasympathetic division (par'-a-sim-pa-THET-ik) One of the two
subdivisions of the autonomic nervous system, having cell bodies
of preganglionic neurons in nuclei in the brain stem and in the
lateral gray horn of the sacral portion of the spinal cord; primarily
concerned with activities that conserve and restore body energy.
Parathyroid gland (par'-a-THT-royd) One of usually four small endo-
crine glands embedded in the posterior surfaces of the lateral
lobes of the thyroid gland.
Parathyroid hormone (PTH) A hormone secreted by the chief (princi-
pal) cells of the parathyroid glands that increases blood calcium
level and decreases blood phosphate level.
Parenchyma (par-EN-ki-ma) The functional parts of any organ, as
opposed to tissue that forms its stroma or framework.
Parietal (pa-RT-e-tal) Pertaining to or forming the outer wall of a body
Parietal cell A type of secretory cell in gastric glands that produces
hydrochloric acid and intrinsic factor. Also called an oxyntic cell.
Parkinson disease (PD) Progressive degeneration of the basal gan-
glia and substantia nigra of the cerebrum resulting in decreased
production of dopamine (DA) that leads to tremor, slowing of
voluntary movements, and muscle weakness.
Parotid gland (pa-ROT-id) One of the paired salivary glands located
inferior and anterior to the ears and connected to the oral cavity
via a duct that opens into the inside of the cheek opposite the
maxillary (upper) second molar tooth.
Parturition (par'-too-RISH-un) Act of giving birth to young; childbirth,
Patellar reflex (pa-TELL-ar) Extension of the leg by contraction of the
quadriceps femoris muscle in response to tapping the patellar
ligament. Also called the knee jerk reflex.
Patent ductus arteriosus (PA-tent DUK-tus ar-ter-e-O-sus) Congenital
anatomical heart defect in which the fetal connection between
the aorta and pulmonary trunk remains open instead of closing
completely after birth.
Pathogen (PATH-o-jen) A disease-producing microbe.
Pathological anatomy (path'-o-LOJ-i-kal) The study of structural
changes caused by disease.
Pectoral (PEK-to-ral) Pertaining to the chest or breast.
Pediatrician (pe'-de-a-TRISH-un) A physician who specializes in the
care and treatment of children.
Pedicel (PED-i-sel) Footlike structure, as on podocytes of a glomerulus.
Pelvic cavity (PEL-vik) Inferior portion of the abdominopelvic cavity
that contains the urinary bladder, sigmoid colon, rectum, and
internal female and male reproductive structures.
Pelvis The basinlike structure formed by the two hip bones, the
sacrum, and the coccyx. The expanded, proximal portion of the ure-
ter, lying within the kidney and into which the major calyces open.
Penis (PE-nis) The organ of urination and copulation in males; used
to deposit semen into the female vagina.
Pepsin Protein-digesting enzyme secreted by chief cells of the stom-
ach in the inactive form pepsinogen, which is converted to active
pepsin by hydrochloric acid.
Peptic ulcer An ulcer that develops in areas of the gastrointestinal
tract exposed to hydrochloric acid; classified as a gastric ulcer if
in the lesser curvature of the stomach and as a duodenal ulcer if
in the first part of the duodenum.