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Digestion is a physiological process during which the food is mechanically and physiologically broken down in to simple molecules.

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These simple molecules are easily absorbed by the cells. The process by which the animals obtain food is called nutrition.

Nutrition takes place in the following steps

1.Ingestion – The process of intake of food into buccal cavity.

2.Digestion – The process of conversion of food into simple molecules.

3.Absorption – The process of movement of simple molecules through the wall of small intestine to reach blood.

4.Assimilation – The process of conversion of simple molecules into complex molecules that takes place inside the cells that takes place after absorption is called assimilation.

5.Egestion – The process of removal of undigested food from alimentary canal through anus is called egestion. It is also called defecation.

Types of Digestion

Intracellular digestion – The digestion that takes place inside cell is called intracellular digestion. It is seen in protozoan.

Extra cellular digestion – The digestion that takes place out side the cell but inside the lumen of alimentary canal is called extra cellular digestion. It is exhibited in higher multicellular animals.

STRUCTURE OF HUMAN DIGESTIVE SYSTEM

The digestive system of man includes two components

• Alimentary canal or gastrointestinal tract

• Associated or accessory or digestive glands

Alimentary canal- It includes

1. Mouth

2. Esophagus

3. Stomach

4. Small intestine

5. Large intestine.

Digestive glands- It includes

1. Salivary glands

2. Liver

3. Pancreas

Mouth

It is internally lined by non keratinized stratified squamous epithelium. The roof of the buccal cavity is formed by a structure called palate. Palate separates buccal cavity from nasal cavity.

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