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Bile : Bile is a yellow-green fluid, secreted by the liver consists of water, mucus, bile pigment : bilirubin, bile salts : derived from cholic and chenodeoxycholic acid cholesterol.The bile acids,cholic and chenodeoxycholic acid are synthesised by hepatocytes , conjugated (combined) with either glycine or taurine,then secreted into bile as sodium or potassium salts. In the small intestine they emulsify fats ,aiding their digestion . In the terminal ileum most of the bile salts are reabsorbed and return to the liver in the portal vein. This enterohepatic circulation,or recycling of bile salts, ensure that large amounts of bile salts enter the small intestine daily from a relatively small bile acid pool. Bilirubin is one of the products of haemolysis of erythrocytes by Kuppfer cells in the liver and by other macrophages in the spleen and bone marrow. In its original form bilirubin is insoluble in water and is bound of albumin. In hepatocytes it is conjugated to glucuronic acid and becomes water soluble before being excreted in bile. Bacteria in the intestine change the form of bilirubin and most is excreted as stercobilin in the faeces. A small amount is reabsorbed and excreted in urine as urobilin. Jaundice is yellow pigmentation of the tissues, seen in the skin and conjunctiva, caused by excess blood bilirubin . Bile Ducts : The right and left hepatic ducts join to form the common hepatic duct just outside the portal fissure. The hepatic duct passes downwards for about 3 cm where it is joined at an acute angle by the cystic duct from the gall bladder. The cystic and hepatic ducts together form the common bile duct which passes downwards behind the head of the pancreas to be joined by the main pancreatic duct at the ampulla of the bile duct. The opening of the combined ducts into the duodenum is controlled by the sphincter of oddi. The common bile duct is about 7.5cm long and has a diameter of about 6mm.The walls of the bile ducts have same layers of tissue as those described in the general plan of the alimentary canal. In the cystic duct the mucus membrane lining is arranged in irregularly situated circular folds which have the effect of a spiral valve.Bile passes through the cystic duct twice- on its way into the gall bladder to the common bile duct and thence to the duodenum. Gall Bladder : The gall bladder is a pear-shaped sac attached to the posterior surface of the liver by connective tissue. It has a fundus or expanded end, a body or main part and a neck which is continuous with the cystic duct.The gall bladder has the same layers of tissue as those described in the general plan of the alimentary canal, with some modifications. Peritoneum covers only the inferior surface. The gall bladder is in contact with the posterior surface on the right lobe of the liver and is held in place by the visceral peritoneum of the liver. Muscle layer. There is an additional layer of oblique muscle fibres. Muscous membrane displays small rugae when the gall bladder is empty that disappear when it is distended with bile.The cystic artery, a branch of the hepatic artery, supplies blood to the gall bladder. Blood is drained away by the cystic vein, which joins the portal vein. Then, Nerve impulses are conveyed by sympathetic and parasympathetic nerve fibres. It has the same autonomic plexuses as those described in the general plan. Functions of the
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