THE DIGESTIVE SYSTEM FOOD SERVES

Two important purposes for the body

It is a source of materials for the growth and replacement of tissue and a source of fuel for energy. And it is digestion that bridges the gap between what we enjoy as food and what must enter the bloodstream to supply the body with its needs. The digestive process, which takes place in the 3D-foot tube called the alimentary canal, involves both mechanical and chemical changes. It requires the squeezing and pushing of muscles and the action of a series of digestive juices. 

It is interesting; it is understandable; and it is very much worth understanding, for understanding can do much to avoid disturbances and prevent useless anxieties, some of them stirred up by commercial interests in behalf of digestive aids and remedies which, perhaps as often as not, are gulped at considerable expense by those who have no real need for them.

START OF THE PROCESS

 The alimentary canal has five major divisions: (1) mouth; (2) esophagus, or gullet; (3) stomach; (4) small intestine; and (5) colon, or large intestine. The mouth, though many people are not aware of it, has an important role to play in digestion. Here, of course, chunks of food are reduced to small particles as the tongue, itself a bundle of muscles, rolls them around while the incisors and canine teeth in front cut and tear and the molars in back grind.

 In the mouth, too, during chewing, the first digestive chemical change takes place. A p.li r of silliv.uy glands, known as the parotid glands, lie in the sides of the face, in front of and slightly below the ears. Saliva from these glands reaches the mouth through parotid ducts which open on the inner surfaces of the cheeks opposite the second molar teeth.

There are also a pair of sub-maxillary glands in the angles of the lower jaws and a pair of sublingual glands under the tongue. Ducts from these glands open into the floor of the mouth beneath the tongue. Saliva mixes with food in the mouth and softens and lubricates it. Saliva, too, contains a digestive enzyme, ptyalin, which acts to convert cooked starch to sugar. 

This is why, even as you are chewing them, bread and potatoes dissolve. Ptyalin, however, is unable to reach and work on starch grains that are still wrapped in their natural cellulose containers, and this is why starches should be cooked before being eaten.

A word here about enzymes- since these is substances very much involved in the whole process of digestion.