The cystic duct is all about 3-5 cm long and runs backward and downward from the neck of the gallbladder to run in the lesser omentum with common hepatic duct and joins it at an acute angle to create the bile duct.
Its junction with common hepatic duct is generally situated immediately below the porta hepatis.
The mucous membrane lining the inside of the cystic duct is thrown into a series of crescentic folds (5-10 in number). They project into the lumen in a spiral manner creating a spiral fold termed “spiral valve (of Heister)”.
The valve of Heister keeps the duct open so that bile can go through it both in and out of the gallbladder.
When the CBD is closed at its inferior end, the bile secreted by the liver fills the duct and goes through the cystic duct into the gallbladder.
When the CBD is open, the bile flows into it from the common hepatic and cystic ducts.
The flow of bile is enhanced by the contraction of the gallbladder. It’s organized by the easiness of sphincter of CBD below the effect of cholecystokinin, a hormone released by the duodenal mucosa.