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Digestive System

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Living organisms need food

a) In order to keep alive and to carry on their various life activities such as ingestion, digestion, absorption, respiration, movement, circulation, co-ordination, secretion, excretion and reproduction

b) For building and maintaining their cellular and metabolic machinery (growth maintenance and repair of the organism)

c) For regulating metabolic processes.

d) For building up the resistance against disease

Food thus can be defined as any essential substance that when absorbed into the body tissues yields materials for the production of energy, the growth and regulation of life processes, without harming the organism.

1. The particles or pieces of food, small or big are taken into the body. This is called as eating or ingestion.

2. The ingested food is then digested, where the complex and large food particles are broken down into simpler, smaller and soluble molecules.

3. Then, the simpler substances obtained from digestion are then absorbed into the cells of the body.

4. Then the undigested waste material is removed and thrown out of the body by excretion. The process of digestion includes mechanical and chemical breakdown of the ingested food.

The chunks of food chewed by us are broken down into small pieces and are acted upon a variety of enzymes secreted into the mouth. Thus, inside the mouth, saliva moistens the masticated food and causes chemical digestion (of starch by the amylase enzymes into smaller molecules). The masticated food and partially digested food then passes the esophagus or the food pipe into the stomach. Here, it is acted upon by gastric juice of the stomach, which contains hydrochloric acid, pepsin and other enzymes. These enzymes break down the proteins of the food into smaller molecules, which pass onto small intestine.


In the first part of the small intestine, called the duodenum, food (now called chyme) is acted upon the by bile juice from the liver and pancreatic juice from the pancreas. The walls of a part of small intestine called ileum also pour some enzymes for food digestion.

Digestive System

All the food, which is digested by the mouth, stomach, duodenum and ileum, is ultimately absorbed by the villi, which are numerous minute finger like projections into the cavity of the small intestine. The absorbed food is then sent through blood to different parts of the body. The absorbed food materials are utilized by the body in various ways, by a process called assimilation. The undigested food is sent to the large intestine and removed through the rectum and anus in the form of stool or faeces. This process is called excretion.


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