The liver forms 'bile' which passes down through bile duct into the intestines.
End of this bile duct has a sphincter (or a gate) which is closed when there is no
food in the stomach or adjoining small intestine (duodenum). Gall bladder is
attatched to the side of the bile duct. When the stomach & adjoining small
intestine (duodenum) are empty then the opening of bile duct into intestine is
closed, the bile is diverted to gall bladder where it is '
stored' & 'concentrated'.
When food fills the stomach & starts moving into duodenum the opening of bile
duct into intestine is opened. Now the gall bladder 'contracts' to deliver bile into
the intestine.
Gall bladder is a sac like structure (seen here in green
colour). It is placed under the liver just below the lower
margin of the rib cage (seen here as a
red line) and has a
capacity of about 50ml.
To know about Gall bladder Stones CLICK on the picture below