Table of Contents
Pancreas – an elongated gland with both endocrine and exocrine functions that lies beneath the STOMACH on the upper left side of the abdomen, beneath the lower ribs. Both realms of function play roles in digestion, though the endocrine functions of the pancreas are also significant for maintaining the body’s GLUCOSE-INSULIN balance and for regulating cellular use of glucose.
The main body of the pancreas is a loose collection of secretory cells, looking somewhat like a mass of fish eggs, that produce DIGESTIVE ENZYMES and juices. These cells organize in lobular formations, called acini, around ducts that channel their secretions to the main pancreatic duct coursing through the center of the pancreas (hence their designation as exocrine). The pancreatic duct joins the common BILE duct from the GALLBLADDER just before the DUODENUM (the first segment of the SMALL INTESTINE), adding its juices to the bile that then flows into the duodenum.
Interspersed among the secretory cells are about a million clusters of specialized cells that produce the hormones INSULIN, GLUCAGON, and SOMATOSTATIN. Called the ISLETS OF LANGERHANS, these clusters are the endocrine glands of the pancreas. An extensive BLOOD supply infiltrates the islets, which secrete their hormones directly into the bloodstream (hence their designation as endocrine). These hormones regulate numerous functions of METABOLISM throughout the body, including many that take place in the gastrointestinal system.
Pancreatic Enzymes and Juices
The pancreas produces numerous enzymes essential for digestion. DIGESTIVE HORMONES trigger their release. Key among the digestive enzymes are
- proteases, notably trypsin and chymotrypsin, which break down proteins; to protect itself from these proteases hydrolyzing its own tissue, the pancreas secretes them in proenzyme forms, trypsinogen and chymotrypsinogen, that an enzyme in the duodenum, enterokinase, activates
- pancreatic lipase, which breaks down dietary triglyceride into fatty acid molecules the intestinal mucosa can absorb
- amylase, which breaks down dietary starches (plant-based stored carbohydrates) into disaccharides (multiple molecule sugars) in preparation for further digestion later in the small intestine
- ribonuclease and deoxyribonuclease, which break down nucleic acids (chemicals that facilitate the body’s use of proteins)
- elastase, which facilitates the break down of proteins into amino acids
- bicarbonate, which neutralizes gastric acid in the chyme (mixture of food and gastric juices) that flows from the stomach into the duodenum
The primary hormones the pancreas produces are insulin, glucagon, and somatostatin. Insulin is key to carbohydrate and lipid (fatty acid) metabolism, in the gastrointestinal tract as well as at the cellular level throughout the body. The pancreas releases insulin in response to digestive hormones the gastrointestinal tract secretes as food enters the various stages of digestion. Insulin regulates glucose levels in the blood by controlling how much, and when, glucose enters the cells. It also signals the LIVER to convert excess glucose to the storage form glycogen. Somatostatin slows the release of insulin. Glandular tissue in the intestinal mucosa also produces somatostatin, which acts to slow the release of other digestive enzymes as well. The pancreas releases glucagon when blood glucose levels fall. Glucagon signals the liver to convert glycogen to glucose.
Common conditions that can affect the Pancreas
|Common conditions that can affect the Pancreas|
|PANCREATIC CANCER||pancreatic cyst|
|DIABETES||gallstones in the common bile duct|
For further discussion of the pancreas and the functions of the islets of Langerhans within the context of gastrointestinal structure and function, please see the overview section “The Gastrointestinal System.”