Chapter 16 Digestion And Absorption
The digestive system of humans consists of an alimentary canal and associated digestive glands.
The alimentary canal consists of the mouth, buccal cavity, pharynx, oesophagus, stomach, small intestine, large intestine, rectum and anus.
The accessory digestive glands include the salivary glands, the liver and the pancreas.
Inside the mouth, the teeth masticate the food, the tongue tastes the food and manipulates it for proper mastication by mixing it with the saliva. Saliva contains a starch digestive enzyme, salivary amylase that digests the starch and converts it into maltose (disaccharide).
The food then passes into the pharynx and enters the oesophagus in the form of bolus. It is further carried down through the oesophagus by peristalsis into the stomach.
In stomach, mainly protein digestion takes place. Simple sugars, alcohol and medicines are also absorbed in the stomach.
The food enters into the duodenum portion of the small intestine and is acted on by the pancreatic juice, bile and finally by the enzymes in the succus entericus, so that the digestion of carbohydrates, proteins and fats is completed. The digested end products are absorbed into the body through the epithelial lining of the intestinal villi.
The undigested food enters into the caecum of the large intestine. Most of the water is absorbed in the large intestine. The undigested food becomes semi-solid in nature and then enters into the rectum, anal canal and is finally ejected through the anus.