Introduction to Pancreatic Endocrinology

Summary:

The passage discusses the structure and functions of the islets of Langerhans, which are part of the pancreas and have endocrine functions. The pancreas is a mixed gland with both exocrine and endocrine parts, but the focus is on the endocrine part. The islets of Langerhans make up approximately 1% of the pancreas and contain five types of cells: A/Alpha, B/Beta, D/Delta, Epsilon, and F/pp cells. Each type of cell secretes different peptide hormones.

A/Alpha cells are located on the periphery of the islets and secrete glucagon. B/Beta cells are found in the center of the islets and secrete insulin, C-peptide, small amounts of amylin, and proinsulin. D/Delta cells are dispersed throughout the islets and secrete somatostatin, a hormone that inhibits the release of other hormones. Epsilon cells secrete ghrelin, which induces hunger, and F/pp cells secrete pancreatic polypeptide.

The arrangement of blood supply in the islets is described, with arterioles supplying blood to the central beta cells and then dividing into fenestrated capillaries that spread in all directions. This arrangement allows insulin to inhibit alpha cells near them from secreting glucagon.

Overall, the islets of Langerhans play a vital role in regulating hormone secretion in the pancreas, including the production of insulin and glucagon, which are important for glucose metabolism.

Excerpt:

Introduction to Pancreatic Endocrinology

Islets of Langerhans
Pancreas is a mixed gland. It has exocrine and endocrine functions. The exocrine part consists of acinar cells. The endocrine part consists of islets of Langerhans (more abundant in the tail of the pancreas).

More than 1 million islets of Langerhans are present in the pancreas.
Exocrine part: ~99%
Endocrine part: ~1%

Islets of Langerhans comprise five types of cells: A/Alpha, B/Beta, D/Delta, Epsilon and F/pp cells. All types of cells secrete peptide hormones.

A/Alpha Cells
Present in the periphery of the islets. They comprise about 20% of total islet cells, secrete glucagon
B/Beta Cells.

Present in the centre of islets. They comprise about 60% of total islet cells. Secrete insulin, C-peptide, little amylin, and little proinsulin (insulin and C-peptide are always secreted in the same amount, that is, equimolar ratio).