insulin /in″səlin/ [L, insula, island] , 1. a naturally occurring polypeptide hormone secreted by the beta cells of the islets of Langerhans in the pancreas in response to increased levels of glucose in the blood as well as to the parasympathetic nervous system and other stimuli. The hormone acts to regulate the metabolism of glucose and the processes necessary for the intermediary metabolism of fats, carbohydrates, and proteins. Insulin lowers the blood glucose level and promotes transport of glucose into the muscle cells and other tissues. Inadequate secretion of insulin causes elevated blood glucose and triglyceride levels and ketonemia, as well as the characteristic signs of diabetes mellitus, including increased desire to eat, excessive thirst, increased urination, and eventually lethargy and weight loss. Uncorrected severe deficiency of insulin is incompatible with life. Normal findings of insulin assay in adults are levels of 5 to 24 mmU/mL. 2. a pharmacological preparation of the hormone administered in treating diabetes mellitus. The various preparations of insulin available for prescription vary in onset, intensity, and duration of action. Animal source insulins, pork and beef, have been discontinued in the U.S. market. Human insulin is derived by recombinant DNA technology and is termed quick acting, intermediate acting, or long acting. Most replacement insulin is given by subcutaneous injection in individualized dosage schedules and insulin pumps, but insulin also can be replaced intravenously. Adverse reactions include hypoglycemia and insulin shock that result from excess dosage and hyperglycemia and diabetic ketoacidosis from inadequate dosage. Fever, stress, infection, pregnancy, surgery, and hyperthyroidism may significantly increase insulin requirements; liver disease, hypothyroidism, vomiting, and renal disease may decrease them. Blood tests for glucose and ketones are performed to determine the need for adjustment of the dosage or of the schedule of administration. See also human insulin.
