The pancreas produces digestive secretions that pass through the ductus pancreaticus into the uppermost portion of the small intestine. If the duct or orifice is narrowed, for example by common gallstones, the pancreatic secretions back up, which can lead to pancreatitis.
What is the pancreatic duct?
The pancreatic duct is the excretory duct of the exocrine portion of the pancreas. It branches into the acini of the pancreatic parenchyma, where it receives secreted digestive enzymes and transports them to the duodenum. The pancreatic duct opens at the papilla duodeni major (Vateri) in the descending pars of the duodenum.
Anatomy and structure
The pancreatic excretory duct system consists of intralobular and interlobular sections and the main excretory duct, the ductus pancreaticus. Within the acini, small-diameter, low epithelium switch glands begin. In many other salivary glands, strip pieces with cylindrical epithelium follow the switch pieces. Such streak pieces are absent in the pancreas. The pancreatic parenchyma is divided into lobules. Each of these lobules, which consists of several serous acinar glands, is attached to an excretory duct that unites the intercalary pieces. The interlobular sections show a highly prismatic epithelium with short microvilli and secrete neutral, sialomucin-rich mucus. They open into the ductus pancreaticus, which runs longitudinally through the pancreas. Histologically, it resembles the interlobular portions; however, exfoliating cells are present here, and isolated mucoid glands open into it. The ductus pancreaticus major (Wirsungi) is 2 mm thick and in most cases ends on the papilla duodeni major together with the ductus choledochus, the common bile duct. The orifice is formed by a sphincter muscle, the sphincter Oddi. During embryonic development, the pancreas and its excretory ducts are formed by the fusion of the ventral and dorsal pancreatic anlagen. In 6-10% of individuals, this fusion fails to occur and a pancreas divisum is formed. These individuals have a ductus pancreaticus minor or accessorius (Santorini) that opens at the papilla duodeni minor.
Function and Tasks
The ductus pancreaticus transports digestive enzymes produced in the pancreas to the duodenum. These are lipases (for fat digestion), amylases (for carbohydrate cleavage), and proteases. The proteases are released in the form of proenzymes, i.e. inactive precursors. They are activated only in the small intestine to prevent pancreatic autodigestion. These proteases are trypsin, chymotrypsin, elastase, phospholipase A and carboxypeptidase. Bile acids entering the pancreas could also trigger self-digestion. However, the pressure in the pancreatic duct system is higher than that in the bile duct system, which prevents reflux of bile. Fatty and amino acids in the diet cause the production of cholecystokinin in the I cells of the duodenum and jejunum. This, as well as vegetative or neural stimulation, is a stimulus for the pancreatic acinar cells to produce and secrete digestive enzymes. Secretin, which is produced in the S cells of the duodenum when food pulp from the stomach lowers the pH in the duodenum, promotes the release of water, bicarbonate, and mucins in the cells of the pancreatic excretory ducts. Thus, a total of 1000-2000 ml of pancreatic secretions are produced per day, which are moved forward by secretory pressure alone. The pancreatic duct does not contain myoepithelial cells, so it cannot contract.
Diseases
Gallstones and tumors at or adjacent to the papilla duodeni Vateri can obstruct or externally compress the excretory duct. Duodenal diverticula can functionally compromise the sphincter Oddi. In these cases, there is reflux of pancreatic secretions into the pancreas. Proteolytic enzymes are then activated while still within the pancreatic ductal system, leading to pancreatic autodigestion, necrosis, and acute pancreatitis. Elastase attacks vascular walls, causing hemorrhage. Lipases and bile acids cause adipose tissue necrosis. Phospholipase A converts lecithin into the cytotoxic lysolecithin. Kallikrein is also formed in the pancreas, among other places. When activated, it leads to a release of bradykinin, which causes vasodilation to shock. Acute pancreatitis has an overall lethality of 10-20%.Trauma can cause rupture of the excretory ducts. Leakage of pancreatic enzymes into the abdomen results in necrosis and peritonitis there. Autodigestive necrosis in the pancreas leads to fibrosis and scarring of the pancreatic ducts in the affected section, and this stenosis in turn increases the risk for recurrence of pancreatitis. The pancreatic tissue anterior to the stenosis atrophies. Although it usually remains asymptomatic, pancreas divisum favors the development of acute or chronic pancreatitis when the papilla duodeni minor has insufficient drainage capacity or is even slightly stenosed, for example, due to focal inflammation. Ductal adenocarcinoma also arises from the epithelial cells of the excretory ducts. It has an overall low incidence of 10 per 100,000 per year, but is by far the most common pancreatic tumor. It is highly malignant and has a high lethality. Pancreatic cancer is most often localized to the pancreatic head, which can lead to stenosis of the intrapancreatic portions of the pancreatic duct and choledochal duct. However, symptoms do not appear until a late phase, so that by the time the diagnosis is made, the tumor is often already inoperable. In contrast, tumors at the papilla Vateri, which have the same histology as pancreatic ductal carcinoma, cause jaundice early on due to the backlog of bile. This leads to a faster diagnosis, which is why these neoplasms have a better prognosis.
Typical and common diseases of the pancreas
- Pancreatitis (inflammation of the pancreas).
- Pancreatic cancer (pancreatic carcinoma)
- Diabetes mellitus
