pancreat

a large, elongated, racemose gland located transversely behind the stomach, between the spleen and duodenum. (See also Plate 11.) It is composed of both exocrine and endocrine tissue. The acini secrete digestive enzymes, and small ductules leading from the acini secrete sodium bicarbonate solution. The combined product, pancreatic juice, enters a long pancreatic duct and from there is transported through the hepatic duct to the duodenum. The pancreatic juice contains enzymes for the breakdown of proteins, carbohydrates, and fats. The bicarbonate ions in the pancreatic secretion help neutralize the acidic chyme that is passed along from the stomach to the duodenum.

Regulation of pancreatic secretion of enzymes and bicarbonate ions is both neural and hormonal; however, the influences of the hormones secretin and cholecystokinin are more important than vagal stimulation. The entry of chyme into the small intestine causes the transformation of an inactive proenzyme, prosecretin, into active secretin that is released from the mucosa of the upper portion of the duodenum. The composition of the partially digested food entering the duodenum influences the amount of each hormone that is released and, therefore, the characteristics of the pancreatic juice.

The endocrine functions of the pancreas are related to the islets of Langerhans located on the surface of the pancreas. These small islands contain three major types of cells: the alpha, beta, and delta cells. The alpha cells secrete the hormone glucagon, which elevates blood sugar. The beta cells secrete insulin, which affects the metabolism of carbohydrates, proteins, and fats. The delta cells secrete somatostatin, the functions of which are not fully understood, but it is known that it can inhibit the secretion of both glucagon and insulin and may act as a controller of metabolic processes. The somatostatin produced by the delta cells of the pancreas is the same as that produced by the hypothalamus as an inhibitor of the release of growth hormone from the pituitary gland.

A compound acinotubular gland located behind the stomach and in front of the first and second lumbar vertebrae. The head lies within the curve of the duodenum, the tail lies near the spleen, and the middle portion constitutes the body. The pancreas is both an exocrine and an endocrine organ. The exocrine glands are acini, each with its own duct; these ducts anastomose to form the main pancreatic duct or duct of Wirsung, which joins the common bile duct and empties into the duodenum at the hepatopancreatic ampulla. An accessory pancreatic duct or duct of Santorini is often present and opens into the duodenum directly. Scattered throughout the exocrine glandular tissue are masses of cells called islets of Langerhans, endocrine glands that secrete hormones. See: illustration

Function

The exocrine secretion of the pancreas consists of enzymes that digest food in the small intestine, and sodium bicarbonate to neutralize hydrochloric acid from the stomach in the duodenum. See: pancreatic juice

The islets of Langerhans contain alpha, beta, and delta cells. Alpha cells secrete glucagon, which raises blood glucose; beta cells secrete insulin, which lowers blood glucose; delta cells secrete somatostatin, which inhibits the secretion of insulin, glucagon, growth hormone from the anterior pituitary, and gastrin from the stomach.

Diseases of the Pancreas

Autoimmune damage to the islets of Langerhans results in type 1 diabetes mellitus, a disease in which insulin secretion is insufficient or completely absent. Insulin-secreting tumors of the pancreas, called insulinomas, produce hypoglycemia; they are exceptionally rare. Inflammation of the pancreas, known as pancreatitis, is a common condition that often results from excessive use of alcohol or from obstruction of the exocrine secretions of the pancreas by gallstones. Pancreas divisum is a common congenital anomaly in which the main duct of the exocrine pancreas drains into an accessory pancreatic papilla instead of the duodenal papilla; it has been associated with recurring episodes of pancreatitis. See: diabetes mellitus; insulin; pancreatic function test

A small mass of pancreatic tissue close to the pancreas but detached from it.

An anomalous condition in which a portion of the pancreas encircles the duodenum.

A congenital anomaly in which the dorsal and ventral pancreatic ducts fail to unite during embryonic development. It has been associated with pancreatitis.

A dorsal outpocketing of the embryonic gut that gives rise to the body and tail of the adult pancreas.

The semidetached lobular part of the posterior surface of a head of the pancreas, sometimes having a separate duct opening into the principal one.

An outgrowth at the angle of the hepatic diverticulum and the embryonic gut that migrates and fuses with the dorsal pancreas. It forms the head of the definitive organ.