Food enters the mouth, passes into the esophagus, and then into the stomach where digestion begins. The pyloric constriction at the posterior end of the stomach separates the stomach form the small intestine. That part of the small intestine immediately following the stomach is the duodenum. The duodenum forms a loop which passes upward under the liver and is continuous with the highly coiled ileum. Near the posterior part of the digestive tract, the intestine is enlarged to form the large intestine .
Enzymes bring about digestion.
Digestion begins in the stomach with materials produced by gastric cells in the stomach lining. As food passes thought the duodenum, it is mixed with alkaline digestive fluid, bile, and pancreatic juices. The bile is secreted by the liver and stored in the gall bladder , a small sac located on the dorsal surface of the liver between the right and left lobes. The pancreatic juices are produced by the pancreas. The pancreas may be partially covered by the middle lobe of the liver.