Q.Discuss the role of the pancreas as a heterocrine (mixed) gland, describing insulin and glucagon and explaining how their antagonistic action maintains blood glucose homeostasis.
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Start your 14-day free trial to unlock the full solution →The pancreas is described as a heterocrine gland because it combines an exocrine portion -- acinar cells secreting digestive enzymes into the duodenum via a duct -- with an endocrine portion, the islets of Langerhans, scattered through the exocrine tissue and secreting hormones directly into the blood. Each islet contains four cell types: alpha cells secreting glucagon, beta cells (the most numerous) secreting insulin, delta cells secreting somatostatin, and PP cells secreting pancreatic polypeptide.
Insulin, released by beta cells in response to a RISE in blood glucose (e.g. after a meal), lowers blood glucose by promoting glucose uptake into cells (especially muscle and fat) and by promoting glycogenesis (glycogen storage), chiefly in the liver; it also promotes fat and protein synthesis, acting overall as the body's principal 'fed state' hormone. Glucagon, released by alpha cells in response to a FALL in blood glucose (e.g. during fasting), raises blood glucose by stimulating glycogenolysis (glycogen breakdown) and gluconeogenesis (new glucose synthesis from non-carbohydrate sources), chiefly in the liver, acting as the body's principal 'fasting state' hormone. Because insulin and glucagon are triggered by opposite blood-glucose conditions and produce opposite effects, their continuously adjusting, antagonistic secretion keeps blood glucose within a fairly narrow normal range acros …
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