Duodenum
First part of small intestine. C shaped 10" long and curves around head of pancreas and entry of common bile duct (accessory organs of digestion, pancreas, liver see below). Chemical degradation of small controlled amounts of food controlled by pyloric sphincter begins here, enzymes secreted by pancreas and duodenum itself aided by emulsifying bile (which also lowers pH). Duodenal ulcers caused by squirting of acid stomach contents into duodenal wall opposite sphincter.