Salivary gland is present in the buccal cavity and it secretes saliva.

The function of mucus is to protect the lining of stomach from the action of hydrochloric acid secreted by stomach lining.

The food components and their simple forms are carbohydrates (glucose), fatty (fats) acids and glycerol, proteins (amino acids).

We use our tongue for talking and taste. Besides, it mixes saliva with the food during chewing and aids in swallowing food. We also taste food with our tongue. It has taste buds that detect different tastes of food.

The villi increase the surface area for absorption of the digested food. Each villus has a network of thin and small blood vessels near to its surface. The surface of the villi absorbs the digested food materials.

The ruminants mainly live on grass and bush which always contain cellulose or roughage. For the splitting of cellulose a lot of chewing and saliva, both are necessary. So, the ruminants need to chew the grass for a long time. So, they chew it twice. If they chew for long while eating, they will get less time to eat.

The organs which are used to intake, to digest and to absorb the food are called digestive organs. The various digestive organs are mouth, buccal cavity, oesophagus, stomach, small intestine, large intestine, liver, gall bladder and pancreas.

Starfish feeds on aquatic animals which are covered by hard shells of calcium carbonate. After opening the shells, the starfish pops out its stomach through its mouth to eat the soft animals inside the shell. After eating the animal, the stomach goes back into the body and the food is slowly digested.

Large intestine is the part of a alimentary canal which is wider and shorter than small intestine. Its main function is to absorb water and some salts from the undigested food. It also helps in the egestion of undigested food.

The first set of teeth grows during infancy and they fall off at the age between six to eight years. This set of teeth is called milk teeth. The second set of teeth that replaces them are the permanent teeth which may last throughout life.

A long tube along the neck and the chest is called a food pipe or oesophagus. The swallowed food passes into the food pipe. Food is pushed down by the movement of the wall of the food pipe. It pushed the food towards stomach.

When the food is not accepted by the stomach then it is vomited out.

Food is pushed into the stomach by the peristaltic movement of the walls of oesophagus. Sometimes the food is not accepted by stomach and then the walls of food pipe move the food in opposite directions and food comes out as vomiting.

This is because the patient cannot digest the food and glucose needs no digestion.