22.9A: Pancreas
The pancreas is a gland organ in the digestive and endocrine systems.
- Describe the function of the pancreas
Key Points
- The pancreas is a gland organ in the digestive and endocrine systems.
- As an endocrine gland, the pancreas produces several important hormones that include insulin, glucagon, somatostatin, and pancreatic polypeptide.
- As a digestive organ, the pancreas secretes pancreatic juice that contains digestive enzymes that assist the absorption of nutrients and digestion in the small intestine.
- These enzymes help to further break down the carbohydrates, proteins, and lipids in the chyme.
Key Terms
- pancreas : A gland near the stomach that secretes a fluid into the duodenum to help with food digestion.
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 that include insulin, glucagon, somatostatin, and pancreatic polypeptide.
As a digestive organ, the pancreas secretes pancreatic juice that contains digestive enzymes that assist the absorption of nutrients and 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 gland. The exocrine function of the pancreas is essential for digestion as it produces many of the enzymes that break down the 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 that 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 that 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 the 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 secretions:
- 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).
- PP cells or gamma cells, secrete pancreatic polypeptide.
The Islets of Langerhans
The islets are a compact collection of endocrine cells arranged in clusters and cords that are crisscrossed by a dense network of capillaries. The capillaries of the islets are lined by layers of endocrine cells that are in direct contact with blood vessels, either by cytoplasmic processes or by direct apposition.
Pancreas : This image shows the location of the pancreas relative to other organs. The pancreas is seen positioned with the duodenum slightly on top of it and next to the right kidney. The pancreas crosses above the left kidney.