Digestive system - 1

line art drawing of the alimentary canal, cleaned up by Micze (Photo credit: Wikipedia)

• How does the body use food?

We have learned that the blood carries nourishment to all the cells in the body. This nourishment comes from the food we eat. Certainly, food as we put it into our mouths could not be carried by the blood. Food has to be greatly changed, before it is able to nourish the tissues.This process of changeis called digestion.

The mouth, oesophagus stomach, small intestine and large intestine form a continuous tube about thirty feet long called the alimentary canal. Food passes through the alimentary canal during the process of  digestion.The liver and the pancreas, two large glands, are also important in the digestion of food.The alimentary canal and these two glands make up the body's digetive system.

• How does digestion begin in the mouth?

One of the constituents of food is starch.When food that contains starch is chewed,the saliva in the mouth brings about a chemical change in the starch. As a result of this change,the starch becomes a kind of sugar that is easy for the body to use as nourishment for the cells.


A substance, such as saliva, that changes food into a form that can be used by the body is called an enzyme.Enzymes are secreted by glands. Saliva is secreted by salivary glands in the roof and floor of the mouth.Only starch can be digested in the mouth. Fats and proteins, the two other main constituents of food, must be digested farther along in the alimentary canal.

• Where is the liver and what does it do?

The liver is a triangular organ which takes up a large part of the right side of the abdomen, just above the waist. 
The liver is a very busy organ. The liver filters out impurities from the blood like kidney.It stores fats and sugars and releases them as they are needed.And it produces digestive  juices like bile,which help the small intestine to break up food and digest it. 

• How do teeth aid digestion?

Since food, whether digested in the mouth or other parts ofthe alimentary canal, must be swall0wed,the food must first be broken up into small pieces. As we chew, our teeth cut and grind food into small pieces that are wetted by saliva, and finally formed by the tongue into lumps that we can easily swallow.

A tooth is a remarkable structure. The part of the tooth above the gum is the crown; below the crown, and covered by the gum, is the neck; below the neck is the root that lies in the socket of the jaw bone. A tooth has an outside covering of enamel, the hardest material in the body, Inside the enamel,and forming the main part of the tooth,is dentine. It looks like bone but is harder. ln a cavity in the center of the tooth is the pulp, which contains blood vessels and nerves.

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