Diabetes
A condition in which excessive amounts of some substances are excreted from the body. The term may refer to either of two unrelated diseases, diabetes mellitus and diabetes insipidus. In common usage, the term diabetes is synonymous with diabetes mellitus.
Diabetes mellitus
This is a disease of abnormal carbohydrate metabolism in which glucose cannot enter the body’s cells and be utilized, and therefore remains in the blood in high concentrations. In diabetes mellitus the excess sugar in the blood (hyperglycemia) leads to the excretion of sugar in the urine (glycosuria), a cardinal diagnostic symptom. Glycosuria in turn causes the excretion of large amounts of urine (polyuria), which results in dehydration and intense thirst (polydipsia). Although blood glucose is high, it cannot enter the appetite-regulating cells of the hypothalamus; hunger is therefore great, and the diabetic person tends to eat constantly (polyphagia). But because glucose cannot enter and nourish the cells, body tissues are subjected to the equivalent of starvation; rapid weight loss occurs, part of which is due to the excretion of water in urine. See also Carbohydrate metabolism.
Diabetes mellitus appears in two varieties, each with its own cause: diabetes mellitus type I (formerly known as juvenile onset diabetes), caused by deficiency of the pancreatic hormone insulin (whose chief function is to promote the entry of glucose into cells); and diabetes mellitus type II (formerly known as maturity onset diabetes), in which insulin is available but cannot be properly utilized. See also Insulin; Pancreas.
Three factors that are believed to be important in the causation of this disease are heredity, viral infections, and immunological damage to the pancreas. Heredity does operate in determining one’s risk of diabetes, but only as a predisposing factor, not as an absolute determinant. The two types of diabetes mellitus have entirely different patterns of inheritance. Virus infection is strongly implicated as one causative factor in the beta-cell destruction that characterizes type I diabetes, but it is not involved in type II diabetes. Some of the viruses that have been implicated are the agents of mumps and rubella (German measles) and coxsackievirus B. Autoimmune reactions, wherein the body’s immune defense system attacks its own pancreatic tissue as though it were a foreign substance, are also suggested as a cause for the beta-cell destruction of type I diabetes. See also Animal virus; Autoimmunity; Human genetics.
Dietary management has been part of diabetic therapy since preinsulin days, when starvation diets were used to prolong the life of type I diabetics. More recently, weight reduction for victims of type II diabetes and complex carbohydrate liberalization for those of both types of diabetes mellitus have been the cornerstone of therapy. Some other dietary measures besides reducing caloric intake are now believed beneficial for type II diabetics. The ingestion of foods high in fiber content, for example, has been shown to reduce hyperglycemia in type II diabetics. For type I diabetics, the traditional diet is high in protein and quite restricted in carbohydrates. Since most type I diabetics are thin, weight reduction is not part of their program.
Diabetes insipidus
Diabetes insipidus is caused by a deficiency of, or resistance to the action of, vasopressin, the antidiuretic hormone produced by the posterior lobe of the pituitary gland. If the pituitary fails to produce vasopressin, the condition is called central diabetes insipidus. If the kidneys do not respond to the vasopressin and fail to concentrate urine, the condition is labeled nephrogenic diabetes insipidus. Symptoms include increased thirst and frequent urination. Permanent damage to the kidneys can result if the condition is not treated.
A low level of vasopressin can be corrected with desmopressin acetate, a synthetic analog of 8-argininevasopressin, which can be administered in the form of a nasal spray. Desmopressin acetate is ineffective in the treatment of nephrogenic diabetes insipidus. See also Neurohypophysis hormone.
