Anatomy of the Pancreas

The pancreas is a gland organ in the digestive and endocrine systems. As an endocrine gland, the pancreas produces several important hormones which include insulin, glucagon, somatostatin and pancreatic polypeptide. As a digestive organ, the pancreas secretes pancreatic juice containing digestive enzymes that assist the absorption of nutrients and the digestion in the small intestine. These enzymes help to further break down the carbohydrates, proteins, and lipids in the chyme.

Location

The pancreas is located posterior to the stomach and next to the duodenum. The pancreas functions as both an exocrine and endocrine. The exocrine function of the pancreas is essential for digestion as the produces many of the enzymes that break down protein, carbohydrates, and fats in digestible foods.

Composition

The pancreas is composed of pancreatic exocrine cells, whose ducts are arranged in clusters called acini. The cells are filled with secretory granules containing the inactivated digestive enzymes, mainly trypsinogen, chymotrypsinogen, pancreatic lipase, and amylase, that are secreted into the lumen of the acini. 

Glandular Function of the Pancreas

The pancreas is a dual-function gland, having features of both endocrine and exocrine glands.

Exocrine Function

The pancreas synthesizes its enzymes in the inactive form, known as zymogens, to avoid digesting itself. The enzymes are activated once they reach the small intestine. The pancreas also secretes bicarbonate ions from the ductal cells to neutralize the acidic chyme that the stomach churns out. The exocrine function of the pancreas is controlled by the hormones gastrin, cholecystokinin, and secretin, which are hormones secreted by cells in the stomach and duodenum in response to food.

The two major proteases which the pancreas synthesizes are trypsinogen and chymotrypsinogen. These zymogens are inactivated forms of trypsin and chymotrypsin. Once released in the intestine, the enzyme enterokinase, which is produced by the intestinal mucosa, activates trypsinogen by cleaving it to form trypsin. The free trypsin then cleaves the rest of the trypsinogen and chymotrypsinogen to their active forms. Pancreatic secretions accumulate in small ducts that drain to the main pancreatic duct, which drains directly into the duodenum.

Endocrine Function

The part of the pancreas with endocrine function is made up of approximately a million cell clusters called islets of Langerhans. Four main cell types exist in the islets. They are relatively difficult to distinguish using standard staining techniques, but they can be classified by their secretion: α cells secrete glucagon (increase glucose in blood), β cells secrete insulin (decrease glucose in blood), delta cells secrete somatostatin (regulates/stops α and β cells), and PP cells or gamma cells, secrete pancreatic polypeptide.

The islets are a compact collection of endocrine cells arranged in clusters and cords and are crisscrossed by a dense network of capillaries. The capillaries of the islets are lined by layers of endocrine cells in direct contact with vessels, and most endocrine cells are in direct contact with blood vessels, either by cytoplasmic processes or by direct apposition. 

Pancreas

Image shows the location of the pancreas relative to other organs.