1.Biliary system dynamics The biliary system dynamics is complex and consists of 3 parts: gallbladder, bile duct and sphincter of Oddi. Its movement is divided into 4 phases according to the site of stimulation: cephalic phase, gastric phase, intestinal phase and ileocolic phase, and is controlled by nerves, hormones and some interacting paracrine factors. The intrahepatic hydrostatic pressure (intrahepatic bile secretion pressure) is (2.64-2.94) kPa, the extrahepatic bile duct internal pressure is (0.98-1.37) kPa, and the sphincter of Oddi pressure is (1.07-1.47) kPa. When the gallbladder is emptied its internal pressure drops below 0.98 kPa to a minimum of about 0.49 kPa, allowing bile to flow into the gallbladder, before the gallbladder contracts The cervical sphincter and the sphincter of Oddi contract temporarily before the gallbladder contracts, causing the gallbladder pressure to rise to (1.77-2.16)kPa, so that the bile can drain into the common bile duct and duodenum more quickly when the cervical sphincter and the sphincter of Oddi relax. The normal secretion pressure of hepatic bile is the driving force of bile flow, while the regulation of biliary system dynamics relies on the normal motor function of the three parts of bile duct, gallbladder and sphincter of Oddi. (1) Regulation of bile duct motor function There are no smooth muscle cells in the intrahepatic bile ducts, and the rate of smooth muscle cells in the extrahepatic bile ducts: 24% in the common hepatic duct, 53% in the supraduodenal segment of the common bile duct, and 87% in the pancreatic segment, and there are only a few circular or longitudinal smooth muscle bundles in the upper part of the common bile duct, while the common bile duct sphincter is formed in the jugular abdomen. The common bile duct has active elongation and shortening motions, which play an important role in bile transport. The autonomic nerve keeps the bile duct tension normal, and the bile flow depends on the pressure gradient difference in the bile duct. If the common bile duct pressure exceeds 2.94kPa, the diameter of the common bile duct can indirectly reflect the pressure of the common bile duct, and the normal diameter of the common bile duct is (6-8) mm, more than 9 mm is considered as dilated. (2) Regulation of gallbladder motor function The gallbladder is divided into gallbladder base, gallbladder body, gallbladder neck and gallbladder duct, which is about (3-4) cm long and (2-3) mm in diameter. The gallbladder duct near the gallbladder neck has spiral mucosal folds called Hester flap, which is composed of smooth muscle. The gallbladder has a smooth muscle layer composed of longitudinal muscle, oblique muscle and a few loosely arranged circular muscles, and the contraction of the smooth muscle of the gallbladder wall can empty the bile, and the filling of the gallbladder is mainly related to the amount of bile secreted by hepatocytes and the contraction of the sphincter of Oddi.