pancreas

pancreas (păn`krēəs), glandular organ that secretes digestive enzymes and hormones. In humans, the pancreas is a yellowish organ about 7 in. (17.8 cm) long and 1.5 in. (3.8 cm) wide. It lies beneath the stomach and is connected to the small intestine at the duodenum (see digestive system). Most of the pancreatic tissue consists of grapelike clusters of cells that produce a clear fluid (pancreatic juice) that flows into the duodenum through a common duct along with bile from the liver. Pancreatic juice contains three digestive enzymes: tryptase, amylase, and lipase, that, along with intestinal enzymes, complete the digestion of proteins, carbohydrates, and fats, respectively. Scattered among the enzyme-producing cells of the pancreas are small groups of endocrine cells, called the islets of Langerhans, that secrete two hormones, insulin and glucagon. The pancreatic islets contain several types of cells: alpha-2 cells, which produce the hormone glucagon; beta cells, which manufacture the hormone insulin; and alpha-1 cells, which produce the regulatory agent somatostatin. These hormones are secreted directly into the bloodstream, and together, they regulate the level of glucose in the blood. Insulin lowers the blood sugar level and increases the amount of glycogen (stored carbohydrate) in the liver; glucagon has the opposite action. Failure of the insulin-secreting cells to function properly results in diabetes, which can occur in two major forms, the division being between juvenile onset and onset in maturity.

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pancreas

Compound gland functioning as both an exocrine (secreting through a duct) and an endocrine (ductless) gland. It continuously secretes pancreatic juice (containing water, bicarbonate, and enzymes needed to digest carbohydrates, fat, and protein) through the pancreatic duct to the duodenum. Scattered among the enzyme-producing cells are the islets of Langerhans, which secrete insulin and glucagon directly into the bloodstream. Disorders include inflammation (pancreatitis), infections, tumours, and cysts. If more than 80–90% of the pancreas must be removed, the patient will need to take insulin and pancreatic extracts. See also diabetes mellitus; hypoglycemia.

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pancreas

a large elongated glandular organ, situated behind the stomach, that secretes insulin and pancreatic juice

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pancreas [′pan·krē·əs]

(anatomy)

A composite gland in most vertebrates that produces and secretes digestive enzymes, as well as at least two hormones, insulin and glucagon.

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Pancreas

A composite gland in most vertebrates, containing both exocrine cells—which produce and secrete enzymes involved in digestion—and endocrine cells, arranged in separate islets which elaborate at least two distinct hormones, insulin and glucagon, both of which play a role in the regulation of metabolism, and particularly of carbohydrate metabolism. See Carbohydrate metabolism

Anatomy

The pancreas of mammals shows large variations. The extremes are the unique, massive pancreas of humans, and the richly branched organ of the rabbit. Usually, the main duct, the duct of Wirsung, opens into the duodenum very close to the hepatic duct. In humans, the pancreas weighs about 2.5 oz (70 g). It can be divided into head, body, and tail. Accessory pancreases are frequently found anywhere along the small intestine, in the wall of the stomach, and in Meckel's diverticulum.

The exocrine portion of the pancreas shows tubuloalveolar glands. Each terminal alveolus is called an acinus. The various acini have central cavities, which open into intralobular ducts through narrow intercalated tubes. The interlobular ducts anastomose and ultimately form the main duct of Wirsung. The activity of the acini is stimulated by secretin as well as by pilocarpine.

The endocrine portion shows cellular masses called islands or islets of Langerhans, in which the cellular cords or masses are more or less isolated by irregular spaces filled with connective tissue and blood capillaries. The two main types of cells are the alpha and the beta cells.

Between the grapelike exocrine portion with its ducts and the islands of Langerhans, it is possible to observe connective tissue septa, numerous blood vessels, and nerves.

Physiology

The pancreatic juice carried to the duodenum is a slightly alkaline liquid containing trypsinogen, which, when activated, causes the hydrolysis of the proteins into amino acids, amylase, and maltase, which act on the glucides, and lipase, which causes the hydrolysis of fatty substances. The intense stimulation of the pancreatic secretion after ingestion of food is considered to be the result of a nervous reflex originating in the mouth, and also of direct introduction of acids and fats into the duodenum, causing the liberation of a hormone called secretin into the bloodstream to stimulate the exocrine secretion.

F. Banting and C. Best (1922) prepared pancreatic extracts which were able to prevent the lethal effects of pancreatectomy. The same effect was obtained with extracts from pancreas in which, after ligature of the duct of Wirsung, the exocrine portion of the gland had disappeared.

The alpha cells and beta cells in the islets are the sources of two hormones, insulin from the beta, and glucagon, also known as the hyperglycemic factor, from the alpha. The former is a hormone which influences carbohydrate metabolism, enabling the organism to utilize sugar. The latter accelerates the conversion of liver glycogen into glucose. Glucagon elevates the blood sugar level, and its effects are the opposite of those of insulin, so that the two hormones together maintain the sugar metabolism of the body in balance. When the level of sugar in the blood becomes too low, the secretion of glucagon is stimulated. See Glucagon, Insulin