There are two different types of tissue in the pancreas. The exocrine pancreas produces enzymes that break down digestible foods (primarily protease, lipase, and carbohydrase), while the endocrine pancreas secretes hormones that regulate blood glucose levels.
The hormone-producing beta-cells are grouped together in the Islets of Langerhans, which make up approximately 1 to 2% of the pancreas. There are about one million islets in a healthy adult human pancreas, which are interspersed evenly throughout the organ, and their combined weight is 1 to 1.5 grams. Each islet contains approximately one thousand cells.
Hormones produced in the Islets of Langerhans are secreted directly into the blood flow by (at least) four different types of cells:Edit
- Beta cells ("B cells") producing insulin and amylin (65-80% of the islet cells)
- Alpha cells ("A cells") releasing glucagon (15-20%)
- Delta cells ("D cells") producing somatostatin (3-10%)
- PP cells containing polypeptide (1%)
The islets are crisscrossed by a dense network of capillaries, so that most endocrine cells can spill the hormones they produce directly into the tiny blood vessels.
The pancreas helps maintain blood glucose concentration within strict limits. Insulin is released in response to rising levels, encouraging glucose uptake and utilisation in insulin-sensitive tissues and cells. Glucagon in contrast increases blood glucose concentration by encouraging hepatic glucose breakdown and release.