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Human Body
-Organs of the Digestive System
The digestive system is composed of the alimentary canal and accessory organs which contribute their secretions to the tract. The digestion of food begins in the mouth and ends in the bowel. The passage (tract) from the mouth to the rectum (the end portion of the bowel) is called gastrointestinal tract which is like a tube, about 9 metres in length, elaborately looped and coiled within the body. Various processing stations are located along the way to prepare and process the food and absorb useful materials The accessory organs of the digestive system include salivary glands, the pancreas, the liver and gall bladder.
1. Mouth and Salivary Glands
The first station on the route of the alimentary canal is mouth. Food spends possibly the shortest time of the whole process in the mouth. Nevertheless, it is one of the most important parts of the digestive process, since it is here that the food undergoes its first stage of conversion into a substance which can eventually be more readily absorbed by the cells of the body. Solid food token into the mouth is first broken up into small pieces and then chewed and ground to pulp by the teeth. Grinding the food up is essential to increase the surface area of the food. Saliva enters the mouth through ducts from three pairs of salivary glands which are accessory organs of the digestive system. Saliva contains the enzymes, one of which is ptyalin which starts off the chemical breakdown of starchy foods into sugar. The tongue pushes the food between the teeth, shapes masticated food into a convenient bolus and shoves it downwards to the aesophagus.
2. Aesophagus
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The ground food-mass, lubricated and softened by saliva, passes backwards on the epiglottis into the aesophagus which is a muscular tube about 2.5 cms.in dia and 25 cms. long, leading down through the chest and diaphragm to the stomach. It is a flexible tube and if the mass of food is larger than its diameter, it can expand to accommodate it. Swallowing the moist ball of food is a chain of
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