The endocrine part of the pancreas

The pancreas consists of exocrine and endocrine parts. The endocrine part of the pancreas (pars endocrina pancreatis) is represented by groups of epithelial cells that form uniquely shaped pancreatic islets (islets of Langerhans; insulae pancreaticae), separated from the exocrine part of the gland by thin connective tissue layers. Pancreatic islets are present in all parts of the pancreas, but there are most of them in the tail region. The size of the islets varies from 0.1 to 0.3 mm, and the total mass does not exceed 1/100 of the mass of the pancreas. The total number of islets is from 1 to 2 million. The islets consist of endocrine cells. There are five main types of these cells. The bulk (60-80%) of the cells are beta cells, located mainly in the internal parts of the islets and secreting insulin; alpha cells - 10-30%. They produce glucagon. About 10% are D cells, which secrete somatostatin. A few PP cells, which occupy the periphery of the islets, synthesize pancreatic polypeptide.

Insulin promotes the conversion of glucose into glycogen, enhances carbohydrate metabolism in muscles. Glucagon enhances the formation of triglycerides from fatty acids, stimulates their oxidation in hepatocytes. With an increase in the concentration of glucose in the blood flowing through the pancreas, insulin secretion increases and the glucose level in the blood decreases. Somatostatin inhibits the production of somatotropic hormone by the pituitary gland, as well as the secretion of insulin and glucagon by A- and B-cells. Pancreatic polypeptides stimulate the secretion of gastric and pancreatic juice by exocrine cells of the pancreas.

The pancreatic islets develop from the same epithelial rudiment of the primary intestine as the exocrine pancreas. They are richly supplied with blood from large blood capillaries that surround the islets and penetrate between the cells.