Caption: Insulin crystals. Insulin is a polypeptide hormone that regulates carbohydrate metabolism. It also takes part in the metabolism of fat (triglycerides) and proteins. It has anabolic properties and also affects other tissues. Insulin is used medically in some forms of diabetes mellitus. Patients with Type 1 diabetes mellitus depend on exogenous insulin (injected subcutaneously) for their survival because of an absolute deficiency of the hormone; patients with Type 2 diabetes mellitus have either relatively low insulin production or insulin resistance, and occasionally require insulin administration if other medications are inadequate in controlling blood glucose levels. Insulin is synthesized in humans and other mammals within the beta cells (B-cells) of the islets of Langerhans in the pancreas. One to three million islets of Langerhans (pancreatic islets) form the endocrine part of the pancreas, which is primarily an exocrine gland. Within the islets of Langerhans, beta cells constitute 60-80% of all the cells. Insulin is built from 51 amino acids and is one of the smallest proteins known. Insulin is produced as a prohormone molecule - proinsulin - that is later transformed by proteolytic action into the active hormone. The actions of insulin on the global human metabolism level include: cellular intake of certain substances, most prominently glucose; increase of DNA replication and protein synthesis; modification of the activity of numerous enzymes (allosteric effect).
Magnification*: x30
Type: LM
Copyright 1985 Dennis Kunkel Microscopy, Inc.
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