膵臓

The pancreas is a pinkish-gray organ located behind the stomach, extending from the duodenum to the spleen. It is firmly bound to the posterior wall of the abdominal cavity. The organ has three main regions: a broad head within the duodenum loop, a slender body, and a short, rounded tail.

The pancreas is divided into exocrine and endocrine parts. The exocrine portion contains acini that produce pancreatic juice through ducts, while the endocrine portion consists of pancreatic islets, or islets of Langerhans. These islets secrete hormones like insulin and glucagon that regulate glucose levels.

Pancreatic juice is transported through the large pancreatic duct and an accessory duct. The main duct meets the bile duct at the duodenal ampulla, where the sphincter of the hepatopancreatic ampulla, or sphincter of Oddi, regulates passage into the duodenum. The accessory duct bypasses the ampulla and opens directly into the duodenum.

Acinar cells in the exocrine pancreas are packed with rough endoplasmic reticulum and zymogen granules. These granules store inactive digestive enzymes that are later activated in the small intestine. This cellular organization allows efficient synthesis and storage of the enzyme-rich pancreatic juice.

The sphincter of the hepatopancreatic ampulla, also called the sphincter of Oddi, regulates the passage of both pancreatic juice and bile into the duodenum. Located at the mouth of the duodenal ampulla, this muscular valve controls the timing and flow of these digestive secretions into the small intestine.

Pancreatic islets, or islets of Langerhans, are mini-endocrine glands scattered throughout the pancreas that secrete hormones like insulin and glucagon. In contrast, acinar tissue comprises the exocrine portion that produces enzyme-rich pancreatic juice. These two tissue types serve distinct metabolic and digestive functions.

Pancreatic enzymes are stored in an inactive form within zymogen granules inside acinar cells. These inactive enzymes are released as part of pancreatic juice and transported to the duodenum. Once in the small intestine, they are activated to perform mechanical and chemical digestion of food.