Download PROCESS OF NUTRITION Nutrition involves five steps. 1

PROCESS OF NUTRITION
Nutrition involves five steps.
1. Ingestion: It is the process of taking food inside the body. Inside the mouth, teeth chew and masticate
the food into smaller pieces.
2. Digestion: It is the process of conversion of large, complex and insoluble organic materials into
simpler, smaller and soluble molecules.
a. Digestion in mouth: In the mouth, food gets mixed up with saliva secreted by salivary glands.
Saliva contains an enzyme salivary amylase or ptyalin which breaks complex carbohydrates like
starch into simpler sugars.
The food is passed to the oesophagus which is lined internally with mucous secreting
cells.(Mucus helps in peristaltic movement of food.)
b. Digestion in stomach: In the stomach, the gastric wall secretes gastric juice. These release
hydrochloric acid, a protein digesting enzyme called pepsin and mucus.
Hydrochloric acid gives an acidic medium which is essential for the activity of gastric enzymes. It
also kills bacteria present in food.
Pepsin is a protein digesting enzyme.
Mucus protects the inner lining of the stomach from the action of the acid under normal
conditions.
c. Digestion in small intestine: The digested food moves from stomach to duodenum of the small
intestine. It receives bile juice from liver and pancreatic juice from pancreas. Since these
secretions are alkaline, the acidity is neutralized and pepsin is inactivated.
Bile contains bile pigments and bile salts. Bile salts help in breaking down oil droplets into small
globules forming emulsion to facilitate further digestion of fats.
Pancreatic juice contains trypsin for digesting proteins and lipase for breaking down fats.
The walls of the intestine contain glands that secrete intestinal juice. The enzymes present in it
finally convert proteins to amino acids, complex carbohydrates into glucose and fats into fatty
acid and glycerol.
3. Absorption: It is the process of mixing of digested food in the body fluid. The intestinal lining is
provided with finger like projections called villi which are richly supplied with blood capillaries. These
blood capillaries take the absorbed food to each and every cell of the body. Villi increase the surface
area of absorption.
4.Assimilation: It is the process of utilization of absorbed food for various body functions like building up
of new tissues ,repairing of old tissues ,synthesis of carbohydrates, proteins and fats inside the cells.
5. Egestion: It is the process of elimination of undigested food from the body through the anus.The villi
present in large intestine helps in absorbing water from undigested food. The exit of waste material is
regulated by anal sphincter.