Composition of the extrahepatic bile duct

In daily life, everyone may have some problems with their body, whether it is from the liver, gallbladder, common hepatic duct, or common bile duct. Many people are more concerned about their composition, because after understanding these components, they will have a thorough understanding of the structure of the body, and can also avoid some functional disorders of the excretion system, which is good for all aspects of the body.

Gallbladder, common hepatic duct and common bile duct.

(1) Gallbladder: It is pear-shaped and located in front of the right longitudinal groove under the liver. It is connected to the common bile duct by the cystic duct. The part of the gallbladder exposed at the front edge of the liver is called the gallbladder fundus. Its surface projection is at the junction of the outer edge of the right rectus abdominis muscle and the costal arch.

(2) Common hepatic duct and common bile duct: The left and right hepatic ducts of the left and right lobes of the liver merge into the common hepatic duct after leaving the porta hepatis. The common hepatic duct and the cystic duct merge into the common bile duct. The common bile duct is about 6 to 8 cm long. It runs down within the hepatoduodenal ligament behind the duodenal bulb and the head of the pancreas. Its terminal end merges with the pancreatic duct and expands into the ampulla of Vater, opening in the descending duodenum and surrounded by the sphincter of Oddi.

The bile secreted by liver cells usually flows into the gallbladder through the common hepatic duct for storage and concentration. When eating, the sphincter of Oddi opens and the gallbladder contracts, prompting bile to flow into the duodenum through the common bile duct. Compression of any part of the hepatic duct, common hepatic duct or common bile duct may cause bile excretion disorders and obstructive jaundice.

Biliary tract anatomy

Except for the normal gallbladder, which has an absorption function and sphincter-mediated storage function, the rest of the extrahepatic biliary system is a group of passive ducts with no functional smooth muscle fibers in the bile duct wall. Secretin can stimulate the bile duct to secrete high concentrations of bicarbonate and affect the total amount of bile to varying degrees.

The ampulla of Vater is composed of the bile duct, the terminal intramural segment of the pancreatic duct, 2 to 3 sphincters, and the surrounding soft tissue.

The sphincter of Oddi surrounds the bile duct, pancreatic duct, and their common passage, and each duct has its own independent (not constant) sphincter. These sphincters have a basal tension of up to 10 mmHg, have phasic peak potentials that are independent of duodenal smooth muscle activity, and have the ability to respond to very small amounts of hormones, gastrointestinal peptides, anticholesterol drugs, and other drugs.

There is an increasing understanding of the importance of these sphincters at the confluence of bile, pancreatic juice, and food and their delicate regulation of function. A normal sphincter can release bile and pancreatic enzymes in time when food passes through, and store bile in the gallbladder when the stomach is empty. Under normal circumstances, the bile and pancreatic systems are independent, that is, bile does not flow back into the pancreatic duct.