We take food and digestion takes place. The useful substances from digested food are absorbed

Digestion:

• It is the breakdown of large insoluble food molecules into small water-soluble food molecules so that they can be absorbed into the watery blood plasma.
• Digestion begins in the mouth with chewing and ends in the small intestine.

Key Points

Functions of various organs associated with digestion:

Stomach:

• It holds food while it is being mixed with enzymes that continue the process of breaking down food into a usable form. 
• It also secretes acids and enzymes that digest food. 

Small Intestine:

• Here 90% of the digestion and absorption of food occurs, the other 10% takes place in the stomach and large intestine.
• The main function of the wall of the small intestine is the absorption of nutrients and minerals from food.
• The small intestine is the "workhorse" of digestion.

Large intestine:

• Absorbing water and electrolytes, producing and absorbing vitamins are three main functions of the large intestine.

Liver:

• The main function of the liver is within the digestive system is to process the nutrients absorbed from the small intestine. 

Thus, it becomes clear that the useful substances from digested food are absorbed by the wall of the small intestine.