The body’s cells can only make use of a narrow range of simple molecules to fuel their activities. However, the food we eat is a mixture of complex compounds.

The function of the digestive system is to break down the constituents of food into simple substances, absorb useful nutrients and dispose of the unwanted residue.

In the digestive system:

• carbohydrates are converted into simple sugars
• proteins are converted into amino acids
• fats are converted into glycerol and fatty acids.

These substances are absorbed into the blood stream and transported to the liver. Further processes occurring in the liver produce the simple molecules that the body’s cells can use.