Diverticulum (dT-ver-TIK-Q-lum) A sac or pouch in the wall of a canal
or organ, especially in the colon.
Dominant allele An allele that overrides the influence of an alter-
nate allele on the homologous chromosome; the allele that is
Dorsiflexion (dor'-si-FLEK-shun) Bending the foot in the direction of
the dorsum (upper surface).
Ductus arteriosus (DUK-tus ar-te-re-O-sus) A small vessel connecting
the pulmonary trunk with the aorta; found only in the fetus.
Ductus (vas) deferens (DEF-er-ens) The duct that carries sperm from
the epididymis to the ejaculatory duct. Also called the seminal duct.
Ductus epididymis (ep'-i-DID-i-mis) A tightly coiled tube inside the
epididymis, distinguished into a head, body, and tail, in which
sperm undergo maturation.
Ductus venosus (ve-NO-sus) A small vessel in the fetus that helps the
circulation bypass the liver.
doo-OD-e-num) The first 25 cm (10
in.) of the small intestine, which connects the stomach and the
Dura mater (DOO-ra MA-ter) The outermost of the three meninges
(coverings) of the brain and spinal cord.
Dynamic equilibrium (e-kwi-LIB-re-um) The maintenance of body
position, mainly the head, in response to sudden movements
such as rotation.
Dysfunction (dis-FUNK-shun) Absence of completely normal func-
Dysmenorrhea (dis'-men-o-RE-a) Painful menstruation.
Dyspnea (DISP-ne-a) Shortness of breath.
Eardrum A thin, semitransparent partition of fibrous connective
tissue between the external auditory meatus and the middle ear.
Also called the tympanic membrane.
Ectoderm The primary germ layer that gives rise to the nervous
system and the epidermis of skin and its derivatives.
Ectopic (ek-TOP-ik) Out of the normal location, as in ectopic preg-
Edema (e-DE-ma) An abnormal accumulation of interstitial fluid.
Effector (e-FEK-tor) An organ of the body, either a muscle or a gland,
that is innervated by somatic or autonomic motor neurons.
Efferent arteriole (EF-er-ent ar-TE-re-ol) A vessel of the renal vascular
system that carries blood from a glomerulus to a peritubular
Efferent ducts (EF-er-ent) A series of coiled tubes that transport
sperm from the rete testis to the epididymis.
Ejaculation (e-jak-u-LA-shun) The reflex ejection or expulsion of
semen from the penis.
Ejaculatory duct (e-JAK-u-la-to-re) A tube that transports sperm from
the ductus (vas) deferens to the prostatic urethra.
Elasticity (e-las-TIS-i-te) The ability of a tissue to return to its original
shape after contraction or extension.
Electrocardiogram (ECG or EKG) (e-lek'-tro-KAR-de-o-gram) A record-
ing of the electrical changes that accompany the cardiac cycle
that can be detected at the surface of the body; may be resting,
stress, or ambulatory.
Electroencephalogram (EEG) (e-lek'-tro-en-SEF-a-lo-gram) A recording
of the electrical activity of the brain from the scalp surface; used
to diagnose certain diseases (such as epilepsy), furnish informa-
tion regarding sleep and wakefulness, and confirm brain death.
Electrolyte (e-LEK-tro-lTt) Any compound that separates into ions
when dissolved in water and that conducts electricity.
Electromyography (e-lek'-tro-mT-OG-ra-fe) Evaluation of the electrical
activity of resting and contracting muscle to ascertain causes of
muscular weakness, paralysis, involuntary twitching, and abnormal
levels of muscle enzymes; also used as part of biofeedback studies.
Electron transport chain A sequence of electron carrier molecules
on the inner mitochondrial membrane that undergo oxidation
and reduction as they synthesize ATP.
Elevation (el-e-VA-shun) Movement in which a part of the body
Embolism (EM-bo-lizm) Obstruction or closure of a vessel by an embolus.
Embolus (EM-bo-lus) A blood clot, bubble of air or fat from broken
bones, mass of bacteria, or other debris or foreign material trans-
ported by the blood.
Embryo (EM-bre-o) The young of any organism in an early stage of
development; in humans, the developing organism from fertiliza-
tion to the end of the eighth week of development.
Embryology (em'-bre-OL-o-je) The study of development from the
fertilized egg to the end of the eighth week of development.
Emesis (EM-e-sis) Vomiting.
Emigration (em'-e-GRA-shun) Process whereby white blood cells
(WBCs) leave the bloodstream by rolling along the endothelium,
sticking to it, and squeezing between the endothelial cells. Adhe-
sion molecules help WBCs stick to the endothelium. Also known
as migration or extravasation.
Emission (e-MISH-un) Propulsion of sperm into the urethra due to
peristaltic contractions of the ducts of the testes, epididymides,
and ductus (vas) deferens as a result of sympathetic stimulation.
Emmetropia (em'-e-TRO-pe-a) Normal vision in which light rays are
focused exactly on the retina.
Emphysema (em'-fi'-SE-ma) A lung disorder in which alveolar walls
disintegrate, producing abnormally large air spaces and loss of
elasticity in the lungs; typically caused by exposure to cigarette
Emulsification (e-mul'-si-fi-KA-shun) The dispersion of large lipid
globules into smaller, uniformly distributed particles in the pres-
ence of bile.
Enamel (e-NAM-el) The hard, white substance covering the crown of
Endocardium (en-do-KAR-de-um) The layer of the heart wall, com-
posed of endothelium and connective tissue, that lines the inside
of the heart and covers the valves and tendons that hold the
Endochondral ossification (en'-do-KON-dral os'-i-fi-KA-shun) The
replacement of cartilage by bone. Also called intracartilaginous