Nutrition in Human Beings:

In humans, digestion of food takes place in the alimentary canal, made up of various organs and glands.

In the mouth, food is crushed into small particles through chewing and mixed with saliva, which contains amylase for digesting starch.

On swallowing, food passes through the pharynx and oesophagus to reach the stomach. Gastric juice contains pepsin (for digesting proteins), HCl and mucus.

The hydrochloric acid creates an acidic medium which facilitates the action of the enzyme pepsin. The mucus protects the inner lining of the stomach from the action of the acid under normal conditions.

From the stomach, the food now enters the small intestine. The small intestine is the site of the complete digestion of carbohydrates, proteins and fats.

The liver secretes bile which emulsifies fat.

The pancreas secretes pancreatic juice which contains the enzymes amylase, trypsin and lipase for digesting starch, proteins and fats, respectively.

In the small intestine, carbohydrates, proteins and fats are completely digested into glucose, aminoacids, fatty acids and glycerol.

The villi of the small intestine absorb the digested food and supply it to every cell of the body.

The unabsorbed food is sent into the large intestine where more villi absorb water from this material. The rest of the material is removed from the body via the anus.