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Medical and Healthy Living Glossary - D

This page of our online glossary of medical and healthy living is for medical and healthy living terms beginning with the letter 'D'.

Dendrite (Dendron) - Fine projections branching off from a neuron body rhat receive impulses from neighbouring neurons.
Dentine (Dentin) - The tough layer of tooth beneath the enamel.
Dermis (Corium) - The thick layer of living skin beneath the epidermis.
Diabetes Mellitus - A complex metabolic disorder involing carbohydrate, fat and protein. It is the result of a lack of insulin produced by the pancreas, so that sugars are not broken down to release energy. This results in an accumulation of sugar in the blood and urine. Because of this fats are used as an alternative energy source. Diabetes mellitus has two forms: Type I may have a viral trigger caused by an infection which affects the cells in the pancreas which produce insulin. Type II is caused by a lower sensitivity to insulin, is common in older people, and is associated with obesity. The symptoms of diabetes mellitus are tiredness, unusual thirst, frequent passing of water and sweet-smelling urine. Blood and urine tests show high levels of sugar.
Diaphragm - A thin layer of tissue stretched across an opening, especially the flexible sheet of muscle and fibre which separates the chest from the abdomen and moves to pull air into the lungs in respiration. The diaphragm is a muscle which, in breathing, expands and contracts with the walls of the chest.
Diarrhoea (Diarrhea) - Loose or watery bowel movements. Often caused by foodborne illness. Diarrhoea can have a number of causes causes such as types of food or allergy to food, contaminated or poisoned food or infectious diseases, such as dysentery.
Diastole - The part of the process involved in each beat of the heart when its chambers expand and fill with blood. It is the opposite of systole.
Dietary Reference Values (DRVs) - The figures calculated by scientists that are estimates of the average quantities of nutrients needed by different population groups, for example women, adolescents, infants and children. Reference Nutrient Intake (RNI) and Recommended Daily Amount (RDA) are two examples of dietary reference values.
Diphtheria - An infectious disease caused by the bacterium Corynebacterium diphtheriae and commonest in children. The infection causes a membranous lining on the throat, which can interfere with breathing and eating. The toxin produced by the bacterium damages heart tissue and the central nervous system, and it can be fatal if it is not treated. The infection is countered by injection of antitoxin with penicillin or erythromycin given to kill the bacterium. The disease is also highly infectious, and all contacts of the patient need to be tested. Diphtheria can be prevented by vaccination.
Diuretic - Any drug that increases the volume of urine produced and passed by the body. Diuretics are often used to combat fluid retention associated with heart or kidney disease. Caffeine, found in coffee and tea, is a diuretic. Natural diuretics include parsley, celery, asparagus and dandelion leaves.
Diverticulosis - The condition in which there are diverticula in the large intestine, occurring primarily in the lower colon. They are caused by the muscles of the bowel forcing the bowel out through weak points in the wall. It is thought that it may be related to diet. Symptoms are not always produced.
Diverticulum - In general, a pouch extending from a main cavity. Specifically, in the intestine, a sac-like protrusion through the wall, many of which usually develop later in life and are thought to be related to dietary factors. The formation of diverticula is called diverticulosis, and their inflammation is called diverticulitis.
DNA (deoxyribonucleic acid) - A nucleic acid and the primary constituent of chromosomes. It transmits genetic information from parents to offspring in the form of genes. It is a very large molecule comprising two twisted nucleotide chains that can store enormous amounts of information in a stable but not rigid way, i.e. parental traits and characteristics are passed on but evolutionary changes are allowed to occur. It is a blueprint for the body's entire development, starting from a single cell at conception.
Dose-Response - Occurs when there is a correlation between the amount of drug or toxin and its effect on health.
Dysentery - An infection and inflammation of the colon which causes bleeding and diarrhoea. Dysentery occurs mainly in tropical countries. The symptoms include diarrhoea, discharge of blood and pain in the intestines. There are two main types of dysentery: bacillary dysentery, which is caused by the bacterium Shigella in contaminated food, and amoebic dysentery or amoebiasis, which is caused by a parasitic amoeba Entamoeba histolytica spread through contaminated drinking water.