The accessory organs relating to the GI tract are vital for the optimum and efficient digestion of food matter. These organs are the liver, gall bladder and pancreas.
Liver – The largest gland in the body, situated in the upper and right part of the abdominal cavity, stores and releases bile to the duodenum for the emulsification of large fat globules to smaller fat globules to increase surface are for lipases to act on. The bile also neutralises the acidic nature of chyme. Secretin in the duodenum stimulates the secretion of bile from the liver. The liver consists of 3 lobes: left, right and caudate (see diagram). Cells of the liver also convert glucose in the bloodstream received from the GI tract to glycogen for storage
Image of the liver courtesy of Wikipedia under commons licence
Gall bladder – stores bile and is located adjacent to the lower section of the liver. Bile becomes more concentrated in the gall bladder so has a greater effect on fat containing foods. The gall bladder can store ~50ml of bile and reaches the duodenum via the common bile duct. The gall bladder is connected to the liver at the upper portion of the gall bladder (see diagram above)
Pancreas - Secretin in the duodenum stimulates the secretion of pancreatic juces which contain alkaline sodium bicarbonate from the pancreas. This helps to neutralise the acidic nature of the gastric acid. Pancreatic juice also contains enzymes including amylase for digestion of starch; chymotrypsin stimulates proteases for digestion of proteins and pancreatic lipase for digestion of fats. Acini are cell types that produce the pancreatic juice. The pancreas sits across the abdominal posterior wall, transversly. The anterior surface of the pancreas body is covered by the posterior and inferior sides of the stomach which rests upon the pancreas. The posterior surface of the pancreas body, on the other hand, brushes borders with the left kidney, curare of the diaphragm and the aorta.
Image of pancreas location courtesy of Wikipedia under commons licence