What is the main function of the gall bladder?

The primary role of the gall bladder is to store bile, which is produced by the liver. Bile is a digestive fluid that helps emulsify fats, making them easier to digest and absorb in the small intestine. When food containing fats enters the small intestine, the gall bladder releases stored bile, aiding in the digestion process. This storage function allows for a concentrated release of bile as needed, enhancing the efficiency of fat digestion.

The other functions mentioned in the choices relate to different organs: insulin production is associated with the pancreas, blood filtration is a function of the kidneys, and nutrient absorption primarily takes place in the small intestine. Thus, the gall bladder's specialized function of storing bile is crucial for efficient digestion, which highlights why it is the correct answer.