Dalton's law - states that the sum of the partial pressures of each gas in a mixture is equal to the total pressure of the mixture.

Dartos - Greek = flayed or skinned.

Data Set - A data set is a named collection of data that contains individual data units organized (formatted) in a specific and prescribed way.

De novo - Latin: new. Anew, afresh. A "trial de novo" is a retrial.

Death clearance - The process of linking a file of known decedents against a cancer registry file in order to determine all deaths among registrants and to identify deaths from cancer among persons previously unknown to the registry.

Declive - Latin declivitas = slope (cf. clivus).

Decussation - Latin decussatus = crossed like the letter X.

Deep - further from the surface.

Deferens - adjective, Latin = carrying down.

Deglutition - Latin deglutire = to swallow, hence the act of swallowing.
 
Dehiscence - Latin de = away, hiscere = to gape, hence, a separation, a splitting away.

Deltoid - adjective, Greek delta (D). The capital has a triangular shape (cf. the delta of the Nile river).
 
Deltoideus - (G. deltoeides, shaped like the letter delta). The musculus deltoideus, shaped like an inverted delta.

Dendrite - or dendron, Greek = a tree, hence like the branches of a tree. Any of the usually branching protoplasmic processes that conduct impulses toward the body of a nerve cell.
 
Dens - Latin = tooth (cf. dentist), adjective - dental.

Dentate - Latin dens = tooth, hence, having a toothed margin. (L. dentatus, toothed). Notched muscles, e.g., the serrati.
 
Denticulate - Latin dens = tooth, hence, having small tooth-like projections.

Dentine - from Latin dens = tooth; the substance of the tooth surrounding the pulp.

Depress - Latin de = prefix implying descent, and pressum = pressed, hence to press down, and depression = downward movement or a concavity on a surface.

Dermatome - Greek derma = skin, tome = a cutting or division, hence a segment of skin supplied by a single spinal ganglion.

Dermis - Greek = skin, adjective - dermal. The second layer of skin.

Detrusor - Latin detrusio = thrust away.

Dialysis - the diffusion of solutes across a selectively permeable membrane.

Diapedesis - Passage of blood cells (especially white blood cells) through intact capillary walls and into the surrounding tissue.

Diaphragm - The diaphragm is the primary muscle of inspiration. It is a thin, dome-shaped sheet of muscle that inserts into the lower ribs. When it contracts, it pushes downward and spreads out, increasing the vertical dimension of the chest cavity and driving up abdominal pressure. This increase in pressure drives the abdominal contents down and out, which in turn increases the transverse size of the chest cavity.

Diaphysis - Greek dia = apart, and physis = growth, hence, the body of a long bone between the growing regions near the ends.

Diarrhea - Frequent, loose, and watery bowel movements. Common causes include gastrointestinal infections, irritable bowel syndrome, medicines, and malabsorption.

Diastole - a relaxation event of either the atria or ventricles. Greek dia = apart, and stellein = sending, hence sending the walls of the heart apart, i.e. relaxation or dilatation. Adjective - diastolic.

Diencephalon - connects the cerebrum to the brain stem. Greek dia = between, and enkephalos = brain, hence in general the structures surrounding the 3rd ventricle. adjective - diencephalic.

Diethylstilbestrol (des) - A drug given to pregnant women from the early 1940s until 1971 to help with common problems during pregnancy. The drug has been linked to cancer of the cervix or vagina in women whose mother took the drug while pregnant.

Differential - In performing the blood count, a total of 100 cells are counted. The percent of each type found in these 100 cells is the cell "differential" for each type.

Differentiation - In cancer, differentiation refers to how mature (developed) the cancer cells are in a tumor. Differentiated tumor cells resemble normal cells and grow at a slower rate than undifferentiated tumor cells, which lack the structure and function of normal cells and grow uncontrollably.

Diffusion - the net movement of substances from an area of higher concentration to an area of lower concentration.

Digastric - adjective, Greek dia = double, and gaster = belly, hence, 2-bellied.

Digastricus - (G. di, two + gaster, belly). Denoting muscles with two fleshy parts separated by a tendinous intersection, e.g., musculus digastricus.

Digestive system - broken into two parts is responsible for the digestion and absorption of nutrients.

Digit - Latin digitus = a finger or toe, usually excepting the pollex (thumb) or hallux (big toe), adjective - digital.

Dilatores - (ME. dilaten, to dilate or expand). Denoting a muscle that opens an orifice.

Diplo - Greek = fold, hence the cancellous bone between the inner and outer tables of the skull, adjective - diploic.

Diploid - Individual or cell having two complete sets of chromosomes.

Diplopia - Greek diploos = double, and opsis = vision, hence double vision.

Disaccharide - a carbohydrate consisting of two linked sugar molecules.

Discus - Latin = disc.

Disease index - A computerized listing of patients seen in a hospital (inpatient and outpatient) organized by discharge diagnosis code. For example: unspecified hypertension is coded 401.9 (in ICD-9, but is I10 in ICD-10) and malignant neoplasm of the central portion of the female breast is coded 174.1 (in ICD-9, but is C50.1 in ICD-10).

Disease registry - An organized system for the collection, storage, analysis, and interpretation of data on persons with the particular disease of concern.

Dissection - Latin disssecare = to cut up, from dis = apart, sectum = cut (c.f. anatomy).

Distal - adjective, Latin di = apart, and stans = standing, hence, standing apart, implying farther from a given point, usually the root of a limb.

Diverticulum - Latin = by-road, hence a blind tubular process or sac.
 
DNA (deoxyribonucleic acid) the part of a cell that stores genetic information.
 
Dorsal - Pertaining to, or situated near, the back, or dorsum, of an animal or of one of its parts. Refers to the back of the body.

Dorso - (L. dorsum, back). Muscles related to the dorsal surface of the body, e.g., latissimus dorsi muscle. Also any structure related specifically to the thorax.

Dorsum - Latin = back.

Down syndrome - A combination of birth defects caused by the presence of an extra #21 chromosome in each cell of the body. Many children with Down syndrome also have congenital heart disease—usually atrioventricular canal defect.

Ductus - Latin = duct.

Duodenum - Latin duodenarius = twelve, because it is 12 fingerbreadths long.

Dura - adjective, Latin = hard (cf. durable); dura mater, the tough covering membrane of the central nervous system.

Dysphagia - Difficulty in swallowing. Greek dys = difficult, and phagein = to eat, hence, difficulty in swallowing.