is gall bladder necessary for digestion in human beings? 

if it is....then How can a person suffering from stones in it(so got it removed)

Now can survive......

The gallbladder serves as a bridge between the liver and the small intestine, where the digestion occurs. The gallbladder stores the bile and parcels it out to the small intestine. If the bladder is removed, it doesn't impair the production of needed bile, only its concentration and timed release into the small intestine is somewhat affected. So, doctors advise to take a low fat diet and to avoid large dinner/lunch.