The function of the bile duct is to transport the bile, which is produced in the liver, to both the gallbladder and to the duodenum. In in gallbladder the bile is concentrated - not all of the bile, but a portion of it. When bile is needed, concentrated bile (from the gallbladder( and unconcentrated bile (from within the bile duct) is released into the duodenum for use.
Bile (along with some other components) is necessary to help breakdown and 'mix' fat so that it can be taken up by the body for use. Some bile is also necessary to help stimulate the large intestine - to help eliminate fecal