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Perception of Body
The digestive system is composed of the alimentary tract and accessory organs which contribute their secretions to the tract. The digestion begins in the mouth and ends in the bowel. The passage from the mouth to the rectum is about 9 metres in length.
Mouth, Salivary Glands, Aesophagus
The first station on the alimentary canal is mouth. Saliva from three pairs of salivary glands enters the mouth and mixes with the food. The tongue pushes the food between the teeth for mastication, shapes it into a glob or bolus and shoves it to the aesophagus, a muscular tube about 2.5 cms. in diameter and 25 cms. long, leading down through the chest and diaphragm to the stomach. As the food enters the aesophagus. it is propelled down to the stomach by alternate waves of contraction and relaxation of the muscular tube.
The Stomach
The food has now reached the second processing station on the tract. Stomach is a muscular collapsible bag about 22 cms. in length. It is tucked up in the abdomen at the lower rib-line under the diaphragm. Its wide end is at the top and towards the left while the narrow bottom end is towards the right. It retains food for 3 to 5 hours during which time partial digestion of protein takes place. The inside lining of the stomach contains 35 million gastric glands which secrete 2 to 3 litres of gastric juices containing mucin, hydrochloric acid and enzyme pepsin. Mucin lines the stomach and protects it from the acid and prevents it from being digested.
Duodenum, Small Intestine, Large Intestine (Colon)
The lower end of the stomach which becomes considerably narrower is connected to the small intestine through pyloric valve. The first portion of the small intestine called duodenum is about 16 to 17 cms. long-a C-shaped tube. It passes behind the liver and encircles the head of pancreas. It is the third processing station and an
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