Q.Describe the endocrine role of islets of Langerhans.
The islets of Langerhans are the pancreas's endocrine tissue, with four cell types secreting glucagon, insulin, somatostatin and pancreatic polypeptide.
The pancreas is both exocrine and endocrine; its endocrine role is carried out entirely by clusters of cells called the islets of Langerhans, which hold four distinct cell types.
Step 1. Alpha (D) cells, about 20% of islet cells, secrete glucagon, which stimulates the liver toward glycogenolysis, raising blood glucose level.
Step 2. Beta (E) cells, about 70%, secrete insulin, which stimulates the liver and muscles toward glycogenesis, lowering blood glucose level.
Step 3. Delta (G) cells, about 5%, secrete somatostatin, which inhibits release of both glucagon and insulin, and also reduces gastric secretion, motility and digestive-tract absorption.
Step 4. PP (F) cells, the remaining roughly 5%, secrete pancreatic polypeptide, which inhibits release of pancreatic juice.
The islets of Langerhans' four cell types (alpha, beta, delta, PP) together regulate blood glucose and digestive secretion via glucagon, insulin, somatostatin and pancreatic polypeptide respectively.
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