The Pancreas
The pancreas is an important endocrine gland, secreting hormones that regulate blood glucose levels.
It is also an exocrine gland, producing enzymes responsible for digestion in the small intestine.
Anatomy and Histology
The pancreas consists of about 1 million clusters of cells call the islets of Langerhans. Each is roughly 100-200 um and consists of four major cell types:
- beta (68%) - produce insulin
- alpha (20%) - produce glucagon
- delta (10% - produce somatostatin
- PP (Pancreatic polypeptide) cells (2%) - produce pancreatic polypeptide
The pancreas also contains rare cells called D1 cells, which produce vasoactive intestinal polypeptide, VIP, and enterochromaffin cells, which produce serotonin.
Hormones
The pancreas makes important hormones that are involved in blood glucose regulation.
- insulin is released in response to elevated blood glucose levels
- glucagon is released in response to decreased blood glucose levels
The Pancreas and Digestion
Pancreatic secretion of lipid digesting enzymes is controlled by hormonal signals from the duodenum and jejeunum, including cholesystokinin (CCK). CCK acts both on the gall bladder and pancreas and also decreases gastric motility.
Intestinal cells also produce secretin, causing the pancreas and liver to produce bicarbonate and thereby increase the pH.
The pancreas secretes 1-2 L/d into the small intestine.
Acinar cells secrete digestive enzymes. Proteolytic enzymes are secreted as inactive zymogens, but others, such as alpha-amylase and lipases, are secreted as functional enzymes. Acinar cells also secrete protective enzymes such as pro-colipase and trypsin inhibitor. Acinal cell secretion is controlled by CCK.
Pancreatic duct cells secrete bicarbonate, water, and electrolytes. Duct cell secretion is controlled by secretin.
Diseases and Conditions
- Type I diabetes occurs following of pancreatic beta cells
- Type II diabetes is different.