Insulin is released when glucose concentration in blood is high (e.g. following an intake of carbohydrate-rich diet). Insulin regulates the concentration of glucose and other sugars circulating in blood by stimulating the uptake of glucose by cells in liver, skeletal muscles and fat tissues.
In humans and other vertebrates, the pancreas is a glandular structure that has exocrine and endocrine functions. The exocrine function of the pancreas is basically the production of pancreatic juice that aids in the digestion of complex biomolecules whereas the endocrine function of the pancreas is the production of hormones such as insulin and glucagon. Its production of such hormones makes the pancreas a part of the endocrine system. The cells in the pancreas that carry out endocrine functions are the islets of Langerhans. The two major cells of the islets are the alpha cells and the beta cells. The alpha cells produce glucagon whereas the beta cells make insulin. These hormones are essential in regulating carbohydrate and fat metabolism. Insulin, in particular, regulates the metabolism of carbohydrates and fats by promoting the uptake of glucose from the bloodstream into the skeletal muscles and fat tissues to be stored as glycogen for later use in glycogenolysis. In type 1 diabetic individuals, the beta cells have become non-functional resulting in the insufficiency of insulin that regulates blood sugar levels.
In some teleost fish, insulin is produced by the endocrine cells of Brockmann body.Brockmann body is a teleost endocrine gland consisting of islet tissues, which in turn, is comprised of endocrine cells.
Word origin: Latin insula ( islet of the pancreas) + -in