The islets of Langerhans are the regions of the pancreas that contain many hormone-producing endocrine cells.
- Distinguish between the cell types of the pancreas
- The pancreas reveals two different types of parenchymal tissue: exocrine acini ducts and the endocrine islets of Langerhans.
- The hormones produced in the islets of Langerhans are insulin, glucagon, somatostatin, pancreatic polypeptide, and ghrelin.
- The pancreatic hormones are secreted by alpha, beta, delta, gamma, and epsilon cells.
- somatostatin: A polypeptide hormone, secreted by the pancreas, that inhibits the production of certain other hormones.
- insulin: A polypeptide hormone that regulates carbohydrate metabolism.
- glucagon: A hormone, produced by the pancreas, that opposes the action of insulin by stimulating the production of sugar.
The pancreas is a glandular organ that belongs to both the digestive and the endocrine systems of vertebrates. It is an endocrine gland that produces several important hormones, including insulin, glucagon, somatostatin, and pancreatic polypeptide.
It is also a digestive, exocrine organ, that secretes pancreatic juice that contains digestive enzymes to assist with digestion and the absorption of nutrients in the small intestine. These enzymes help to further break down the carbohydrates, proteins, and lipids in the chyme.
Under a microscope, stained sections of the pancreas reveal two different types of parenchymal tissue. The light-stained clusters of cells are called islets of Langerhans, which produce hormones that underlie the endocrine functions of the pancreas.
The dark-stained cells form acini, connected to ducts. Acinar cells belong to the exocrine pancreas and secrete digestive enzymes into the gut via a system of ducts.
Islets of Langerhans
Islets of Langerhans: A porcine islet of Langerhans. On the left is a brightfield image created using hematoxylin stain; nuclei are dark circles and the acinar pancreatic tissue is darker than the islet tissue. The right image is the same section stained by immunofluorescence against insulin, indicating beta cells.
The pancreatic islets are small islands of cells that produce hormones that regulate blood glucose levels. Hormones produced in the pancreatic islets are secreted directly into the blood flow by five different types of cells. The endocrine cell subsets are:
- Alpha cells that produce glucagon, and make up 15–20% of total islet cells. Glucagon is a hormone that raises blood glucose levels by stimulating the liver to convert its glycogen into glucose.
- Beta cells that produce insulin and amylin, and make up 65–80% of the total islet cells. Insulin lowers blood glucose levels by stimulating cells to take up glucose out of the blood stream. Amylin slows gastric emptying, preventing spikes in blood glucose levels.
- Delta cells that produce somatostatin, and make up 3–10% of the total islet cells. Somatostatin is a hormone that suppresses the release of the other hormones made in the pancreas.
- Gamma cells that produce pancreatic polypeptide, and make up 3–5% of the total islet cells. Pancreatic polypeptide regulates both the endocrine and exocrine pancreatic secretions.
- Epsilon cells that produce ghrelin, and make up less than 1% of the total islet cells. Ghrelin is a protein that stimulates hunger.
The islets of Langerhans can influence each other through paracrine and autocrine communication. The paracrine feedback system is based on the following correlations:
- The insulin hormone activates beta cells and inhibits alpha cells.
- The hormone glucagon activates alpha cells which then activate beta cells and delta cells.
- Somatostatin hormone inhibits alpha cells and beta cells.