The pancreas is a glandular organ located behind the stomach in humans. It combines two functions: its exocrine tissue delivers digestive secretions through ducts into the intestine, while its endocrine tissue releases hormones into the bloodstream. These activities contribute to digestion and the regulation of metabolism, particularly the control of blood glucose. The two components occupy the same organ but differ in their cellular organization and routes of secretion. (ncbi.nlm.nih.gov)
Anatomy and tissue organization
The pancreas extends across the upper abdomen, with its broad head enclosed by the curve of the duodenum, the first portion of the small intestine. A short neck connects the head to the body, which continues toward a tapered tail near the spleen. The uncinate process projects from the lower part of the head. Most of the organ lies behind the peritoneal lining of the abdominal cavity. (ncbi.nlm.nih.gov)
Small ducts collect pancreatic secretions and converge into the main pancreatic duct. This usually joins the common bile duct before opening into the duodenum; an accessory duct may provide another drainage route. The close relationship between the bile duct and pancreatic head explains why swelling or a mass in this region can obstruct bile flow. Arterial supply comes from branches of the celiac and superior mesenteric arteries, while venous drainage enters the portal circulation. (ncbi.nlm.nih.gov)
Most functional pancreatic tissue consists of exocrine acini and ducts. Acini are clusters of secretory cells surrounding small central spaces. Scattered among them are pancreatic islets, also called islets of Langerhans, containing the endocrine cells. Acinar cells manufacture digestive enzymes, whereas duct cells contribute fluid and bicarbonate to the secretion. (ncbi.nlm.nih.gov)
Exocrine function
Pancreatic juice contains enzymes that act on several major food components. Amylase breaks down starch; lipase participates in fat digestion; and proteases, including trypsin and chymotrypsin, break down proteins. Pancreatic nucleases digest nucleic acids. These enzymes act within the intestinal lumen, and some of their products undergo further digestion by enzymes associated with the intestinal lining before absorption. (pancreapedia.org)
Many pancreatic proteases are synthesized and stored as inactive precursors, or zymogens. For example, trypsinogen is converted into trypsin by an enzyme on the duodenal surface, and trypsin then activates additional protease precursors. Storage in secretory granules and the presence of trypsin inhibitors help limit premature enzyme activity within pancreatic tissue. Amylase and lipase, by contrast, are secreted in active forms. (pancreapedia.org)
Ductal bicarbonate neutralizes acid arriving from the stomach, creating conditions suitable for intestinal digestion. Fluid secretion also carries enzymes through the duct system into the intestine. Thus, pancreatic digestive function depends on coordinated enzyme production, ductal transport, and acid neutralization—not simply on the amount of enzyme synthesized. (pancreapedia.org)
Endocrine function
Pancreatic islets release their secretions into nearby blood vessels rather than into the pancreatic ducts. Their principal cell types include beta cells, which produce insulin; alpha cells, which produce glucagon; and delta cells, which produce somatostatin. Other islet cells secrete pancreatic polypeptide, while beta cells also release amylin. These hormones have coordinated effects on the liver, muscle, adipose tissue, and other organs. (pubmed.ncbi.nlm.nih.gov)
Insulin supports glucose uptake and nutrient storage and reduces glucose production by the liver. Glucagon helps increase the availability of circulating glucose, particularly between meals, through effects on hepatic glycogen breakdown and glucose synthesis. Somatostatin inhibits several secretory processes, including insulin and glucagon release. Together, islet hormones contribute to glucose homeostasis, adjusting nutrient handling to changing physiological conditions. (ncbi.nlm.nih.gov)
Regulation of secretion
Pancreatic secretion responds to both neural and hormonal signals. Parasympathetic pathways, particularly those associated with the vagus nerve, participate in meal-related secretion. Intestinal hormones link pancreatic activity to the arrival of stomach contents and nutrients in the small intestine. (ncbi.nlm.nih.gov)
Secretin, released in response to acid in the duodenum, promotes bicarbonate-rich ductal secretion. Cholecystokinin participates in the stimulation of enzyme secretion through interacting neural and hormonal pathways. These signals cooperate rather than acting as completely separate controls, coordinating the delivery of digestive enzymes with the fluid required to transport them. (pancreapedia.org)
Major disorders
Pancreatitis is inflammation of the pancreas. Acute pancreatitis begins suddenly; chronic pancreatitis involves persistent injury and can produce permanent scarring. Gallstones, heavy alcohol use, certain medicines, and genetic disorders are recognized causes. Extensive damage may impair both digestive secretion and endocrine function. (niddk.nih.gov)
Exocrine pancreatic insufficiency occurs when problems with pancreatic enzymes prevent complete intestinal digestion. It can accompany chronic pancreatitis, cystic fibrosis, pancreatic cancer, or pancreatic surgery. Consequences include malabsorption and malnutrition; assessment may include stool elastase measurement and pancreatic function tests. (niddk.nih.gov)
The pancreas also has a central role in diabetes mellitus. In type 1 diabetes, the immune system destroys insulin-producing beta cells. Type 2 diabetes combines impaired tissue responsiveness to insulin with insufficient insulin production. Pancreatic damage or removal can also cause diabetes. (niddk.nih.gov)
Pancreatic cancer includes several distinct tumor types. Most arise in exocrine tissue, with ductal adenocarcinoma the predominant form. Pancreatic neuroendocrine tumors arise from endocrine cells and differ from exocrine cancers in their biological behavior and clinical characteristics. (cancer.gov)