The gall bladder resembles a sac secured along the inferior surface of the liver. The main function of the gall bladder is to store the bile it receives from the liver at an increased concentration than it was received. It successfully stores anywhere from 35 milliliters to about 50 milliliters; the amounts determined and restricted via the sphincter valve at the neck of the gall bladder. The inner layer of the gall bladder, the mucosa layer, is very similar to the inner mucosa layer of the stomach, containing folds within the mucosa. This permits expansion, just like the stomach, however, the gall bladder is expanding with bile rather than food. Fully expanded, the gall bladder resembles a pear.
Bile is the digestive fluid which is made up of mostly bile salts with a yellow-green appearance. Bile also contains biliruben, cholesterol, and a few additional compounds. Biliruben is the product that is left after food is broken down into its molecular structure.
The muscularis is able to eject bile somewhat forcefully with a simple contraction of the muscular tissue. The liver is in constant production of bile, which then of course drains into the hepatic duct to the common bile duct until it finally reaches the duodenum. The gall bladder receives extra bile for storage when the small intestine is devoid of food remnants. In this case, the sphincter muscle (sphincter of ampulla) contracts rapidly to force the remaining bile back into the gall bladder.
The blood supply to the gall bladder is received via the cystic artery, a branch of the right hepatic artery. Venous return happens via the cystic vein, which then joins the hepatic portal vein. The gall bladder and the liver are innervated almost identically. Sympathetic innervation is received via the thoracolumnar nerves through the celiac ganglia. Parasympathetic innervation happens via the vagus nerve.