Medical Dictionary: D

daily value (DV): A measurement, found on the “Nutrition Facts” labels of packaged food, that reports the amounts of specific micronutrients and other key dietary components per serving, stated as a percentage of daily requirements. DVs do not take such factors as age or sex into account, but instead reflect the highest amount of a nutrient an individual might need.

de Quervain’s tendonitis: inflammation of tendons at the wrist that move the thumb.

decibel: A unit of measurement for the loudness of a sound, with the highest decibels indicating the loudest sounds.

declarative memory: Memory for facts (semantic memory) and for events (episodic memory); also called explicit memory.

decoction: An herbal product or tea made by boiling a plant in water, often using the roots and bark.

decongestants: Medications used to relieve the stuffy-nose symptoms of IgE-mediated allergies. Decongestants should be used judiciously; overuse exacerbates the problem.

deep sleep: See slow-wave sleep.

degenerative disk disease: A general term for the age-related deterioration (loss of water and increased brittleness) of the cushioning disks between the vertebrae.

degenerative joint disease: A joint disease common with aging that is characterized by progressive deterioration of the cartilage lining the joints; also called osteoarthritis.

delayed sleep phase syndrome: A daily sleep/wake rhythm in which the onset of sleep and wake times are later than desired; the person tends to go to bed later and get up later each day.

dementia: A progressive decline across multiple cognitive domains, resulting in impairment of everyday function.

demulcent: An agent that soothes irritated tissues and mucous membranes.

dendrite: The small branching part of a neuron that receives electrical impulses from other neurons and relays them to the body (nucleus) of the neuron.

dendrites: The parts of a neuron that receive signals sent via neurotransmitters from other neurons.

dendritic cells: Tentacle-like antigen-presenting cells. They play a crucial role in signaling danger and stimulating the B and T cells of the adaptive immune response.

dermis: Middle layer of skin that contains collagen, elastin, blood and lymph vessels, nerves, hair follicles, and glands that produce sweat and oil, all of which is cushioned in a gelatinous matrix consisting primarily of hyaluronic acid.

desiccated thyroid: A formula of animal thyroid gland that has been dried and powdered. “Desiccate” means to dry out.

detrusor instability: Involuntary contractions of the detrusor muscle while the bladder is filling, resulting in urgency, frequency, or sometimes incontinence.

detrusor muscle: The layer of involuntary muscle in the bladder wall; during urination, it contracts to squeeze urine out of the bladder into the urethra.

detumescence: The softening of an erection.

diabetes: A systemic condition in which a person’s body is unable to convert sugars and other nutrients into energy. Levels of blood glucose, or sugar, are elevated. Excess body weight raises the risk of developing this condition. People with diabetes often experience foot disorders.

diabetic ketoacidosis: A dangerous condition in which the blood becomes acidic due to a buildup of ketones; it arises during severe insulin deficiency.

diabetic retinopathy: A degenerative eye disorder in which small blood vessels in the retina initially leak and subsequently become blocked. Very fragile new vessels develop, but they ultimately bleed and cause scarring.

diastolic blood pressure: The pressure in the arteries while the heart is refilling with blood between beats; the second and lower of the two numbers obtained when blood pressure is measured.

diastolic pressure: The second or lower number in a blood pressure reading; it notes the pressure against arterial walls when the heart is at rest between contractions.

diathermy: Physical therapy using high-frequency electric current, ultrasound, or microwaves to deliver heat to muscles and ligaments.

dietary fiber: The edible, nondigestible component of carbohydrates naturally found in plant food.

dietary reference intakes (DRIs): A comprehensive set of standards for daily intake of essential vitamins and minerals, based on evidence from scores of observational and clinical studies.

dietary supplements: Vitamins, minerals, herbs, amino acids, enzymes, organ tissues, and a few other substances used to bolster diet. Unlike drugs, they are not regulated by the FDA.

digital rectal examination (DRE): A screening test in which the physician inserts a gloved finger into the rectum to feel the prostate for abnormalities.

disk: See intervertebral disk.

diskectomy: The surgical removal of all or part of an intervertebral disk.

diskitis: Inflammation of an intervertebral disk.

diverticula: Finger-shaped pouches protruding off the colon that often develop with age.

diverticulitis: When diverticula become inflamed.

do-not-resuscitate order (DNR): A legal document that tells health care and emergency personnel not to attempt cardiopulmonary resuscitation or defibrillation if you experience cardiac or respiratory arrest.

dopamine: A neurotransmitter that affects movement and influences thought processes, possibly affecting motivation and reward.

Doppler ultrasound: A noninvasive imaging method that uses high-frequency sound waves to view blood vessels and measure how fast blood is flowing through them.

dorsal kyphosis: An abnormal front-to-back curvature of the mid-to-upper spine that can result from compression fractures of vertebrae. Commonly called dowager’s hump.

double blind: A way of conducting a clinical trial in which neither the participants nor the researchers know who is taking the inactive control substance or the active substance being tested.

double-contrast barium enema: A screening test for colorectal cancer that involves taking x-rays of the colon to detect polyps, cancer, inflammatory bowel disease, or other intestinal problems.

drusen: Tiny yellow deposits that form beneath the macula and may indicate early stages of age-related macular degeneration.

dry-powder inhaler: A device for delivering inhaled medication that works differently from a metered-dose inhaler. With a dry-powder inhaler, an aerosol of medicine is created by the force of inhalation rather than by a chemical propellant.

dual energy x-ray absorptiometry (DXA): A test in which x-rays are used to measure bone density and produce an image of the bone; the preferred screening test for osteoporosis.

dual-energy x-ray absorptiometry (DXA): A test in which x-rays limited to two different energies are used to measure bone density.

duct: A channel in the breast that carries milk from the lobule to the nipple during lactation.

duodenitis: Inflammation of the duodenum.

duodenum: The first part of the small intestine, extending from the stomach to the jejunum.

duplex Doppler ultrasound: A diagnostic technique that uses sound waves. It can reveal blood flow problems inside the penis and is sometimes used to help diagnose the cause of erectile dysfunction.

Dupuytren’s disease: a condition that causes abnormal thickening in tissues of the hand, which forces one or more fingers to curl toward the palm.

durable power of attorney: A legal document that allows you to appoint someone to take care of certain tasks, such as managing your money or acting as your agent in health care decisions, at a time that you specify or upon a triggering event.

durable power of attorney: A legal document that describes specific powers a person can exercise on someone else’s behalf, either immediately or at a particular point in time.

dysarthria: A speech disability caused by an injury to the brain centers controlling the face, mouth, neck, or throat; people so affected may be able to understand speech and form the right words in their mind but cannot articulate them.

dysphagia: A difficulty in swallowing; extremely common after a stroke.

dystonia: abnormal muscle tone or tension in one or more muscles.