daughter cells: Genetically identical cells produced by somatic cell division.
deamination: The removal of an amino group from an amino acid.
decarboxylation: The removal of a molecule of carbon dioxide.
decerebrate: Lacking a cerebrum.
decomposition reaction: A chemical reaction that breaks a molecule into smaller fragments.
decubitis ulcers: Ulcers that form where chronic pressure interrupts blood flow to a portion of the skin.
decussate: To cross over to the opposite side, usually referring to the crossover of the descending tracts of the corticospinal pathway on the ventral surface of the medulla oblongata.
defecation: The elimination of fecal wastes.
deglutition: Swallowing.
degradation: Breakdown, catabolism.
dehydration: A reduction in the water content of the body that threatens homeostasis.
dehydration synthesis: The joining of two molecules associated with the removal of a water molecule.
delta cell: A pancreatic islet cell that secretes growth hormone-inhibiting hormone.
dementia: A loss of mental abilities.
demyelination: The loss of the myelin sheath of an axon, normally due to chemical or physical damage to Schwann cells or oligodendrocytes.
denaturation: A temporary or permanent change in the three-dimensional structure of a protein.
dendrite: A sensory process of a neuron.
denticulate ligaments: Supporting fibers that extend laterally from the surface of the spinal cord, tying the pia mater to the dura mater and providing lateral support for the spinal cord.
dentin: The bonelike material that forms the body of a tooth; differs from bone in that it lacks osteocytes and osteons.
deoxyribonucleic acid (DNA): A nucleic acid consisting of a chain of nucleotides that contain the sugar deoxyribose and the nitrogenous bases adenine, guanine, cytosine, and thymine.
deoxyribose: A five-carbon sugar resembling ribose but lacking an oxygen atom.
depolarization: A change in the transmembrane potential from a negative value toward 0 mV.
depression: Inferior (downward) movement of a body part.
dermatitis: An inflammation of the skin.
dermatome: A sensory region monitored by the dorsal rami of a single spinal segment.
dermis: The connective tissue layer beneath the epidermis of the skin.
detrusor muscle: A smooth muscle in the wall of the urinary bladder.
detumescence: The loss of a penile erection.
development: Growth and the acquisition of increasing structural and functional complexity; includes the period from conception to maturity.
diabetes insipidus: Polyuria due to inadequate production of antidiuretic hormone.
diabetes mellitus: Polyuria and glycosuria, most commonly due to the inadequate production of insulin with a resulting elevation of blood glucose levels.
diabetogenic effect: An elevation in blood sugar concentrations after the secretion of growth hormone or glucagon.
dialysis: Diffusion between two solutions of differing solute concentrations across a selectively permeable membrane, which permits the passage of some solutes but not others; regulates the composition of blood.
diapedesis: The movement of white blood cells through the walls of blood vessels by migration between adjacent endothelial cells.
diaphragm: Any muscular partition; the respiratory muscle that separates the thoracic cavity from the abdominopelvic cavity.
diaphysis: The shaft of a long bone.
diarrhea: Abnormally frequent defecation, associated with the production of unusually fluid feces.
diarthrosis: A synovial joint.
diastolic pressure: Pressure measured in the walls of a muscular artery when the left ventricle is in diastole.
diencephalon: A division of the brain that includes the epithalamus, thalamus, and hypothalamus.
differential count: The determination of the relative abundance of each type of white blood cell on the basis of a random sampling of 100 white blood cells.
differentiation: The gradual appearance of characteristic cellular specializations during development as the result of gene activation or repression.
diffusion: Passive molecular movement from an area of higher concentration to an area of lower concentration.
digestion: The chemical breakdown of ingested materials into simple molecules that can be absorbed by the cells of the digestive tract.
digestive system: The digestive tract and associated glands.
digestive tract: An internal passageway that begins at the mouth, ends at the anus, and is lined by a mucous membrane; also called gastrointestinal tract.
dilate: To increase in diameter; to enlarge or expand.
diploid: Having a complete somatic complement of chromosomes (23 pairs in human cells).
disaccharide: A compound formed by the joining of two simple sugars by dehydration synthesis.
dislocation: The forceful displacement of an articulating bone to an abnormal position, generally accompanied by damage to tendons, ligaments, the articular capsule, or other structures.
dissociation: See ionization.
distal: Movement away from the point of attachment or origin; for a limb, away from its attachment to the trunk.
distal convoluted tubule (DCT): The portion of the nephron closest to the connecting tubules and collecting duct; an important site of active secretion.
diuresis: Fluid loss at the kidneys; the production of urine.
divergence: In neural tissue, the spread of information from one neuron to many neurons; an organizational pattern common along sensory pathways of the central nervous system.
diverticulitis: An inflammation of a diverticulum.
diverticulosis: The formation of diverticula in the wall of an organ.
diverticulum: A sac or pouch in the wall of the colon or other organ.
dizygotic twins: Twins that result from the fertilization of two oocytes.
DNA molecule: Two DNA strands wound in a double helix and held together by weak bonds between complementary nitrogenous base pairs.
dominant trait: An allele whose presence will determine the phenotype, regardless of the nature of its companion allele.
dopamine: An important neurotransmitter in the central nervous system.
dorsal: Toward the back, posterior.
dorsal root ganglion: A peripheral nervous system ganglion containing the cell bodies of sensory neurons.
dorsiflexion: The elevation of the superior surface of the foot through movement at the ankle.
Down syndrome: A genetic abnormality resulting from the presence of three copies of chromosome 21; individuals with this condition have characteristic physical and intellectual deficits.
duct: A passageway that delivers exocrine secretions to an epithelial surface.
ductus arteriosus: A vascular connection between the pulmonary trunk and the aorta that functions throughout fetal life; normally closes at birth or shortly thereafter and persists as the ligamentum arteriosum.
ductus deferens: A passageway that carries spermatozoa from the epididymis to the ejaculatory duct.
duodenal ampulla: A chamber that receives bile from the common bile duct and pancreatic secretions from the pancreatic duct.
duodenal papilla: A conical projection from the inner surface of the duodenum that contains the opening of the duodenal ampulla.
duodenum: The proximal 25 cm of the small intestine that contains short villi and submucosal glands.
dura mater: The outermost component of the cranial and spinal meninges.
dynorphin: A powerful neuromodulator, produced in the central nervous system, that blocks pain perception by inhibiting pain pathways.
dyslexia: The impaired ability to comprehend written words.
dysmenorrhea: Painful menstruation.
dysmetria: Difficulty in performing movements due to problems with the interpretation and anticipation of the distance to be covered.
dysuria: Painful urination.