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The process of nutrition in our body takes place in 4 stages --
this is the process of taking in food. In the mouth, digestion starts with chewing. It breaks up large pieces of food into smaller particles that can be swallowed without choking. It is accomplished by teeth, tongue, jaws and saliva. Chewing is controlled by the somatic nerves to the skeletal muscles of the mouth and jaw. Rhythmic chewing motions are reflexly activated by the pressure of food against the gums, hard palate at the roof of the mouth and tongue. Saliva is  secrete by parotid, sub mandibular and sub lingual glands.
complex food materials are broken down into simpler substances for easier absorption of nutrients.
simpler substances are again converted into complex food materials.
The removal of waste materials from the body is called excretion.

the survival of human beings depends on these four processes.
The composition of nutrients vary in different types of feeding. However, for all living organisms, the nutrient comprises the following organic and inorganic components. They are carbohydrates, proteins, lipids, vitamins, minerals and water. Each component has a specific functional role. A well proportioned intake of nu- trients depends on several factors such as stage of growth, sex, health con- dition, bodily activities and environmental situations.