• Parts of the body concerned with the uptake and digestion of food and elimination of indigestible remains form the digestive system, also called ‘alimentary system’.
  • The human digestive system consists of an alimentary canal and many digestive glands.
  • The alimentary canal is a long tube with muscular walls, glandular epithelial lining, and varying diameter.
  • It opens out at the upper and lower ends, and most of it lies in the abdomen in a much-coiled form.



  • Mouth or Buccal Cavity: The mouth has teeth and tongue
  • The tongue has gustatory receptors which perceive the sense of taste.
  • Tongue helps in turning over the food, so that saliva can be properly mixed in it.
  • Salivary glands secrete saliva. Saliva makes the food slippery which makes it easy to swallow the food.
  • Saliva also contains the enzyme salivary amylase or ptyalin. Salivary amylase digests starch and converts it into sucrose.
  • Teeth help in breaking down the food into smaller particles so that swallowing of food becomes easier.

Types of Teeth

  • There are four types of teeth in human beings.
  • The incisor teeth are used for cutting the food.
  • The canine teeth are used for tearing the food and for cracking hard substances.
  • The premolars are used for coarse grinding of food.
  • The molars are used for fine grinding of food.

Parts of The Human Digestive System


  • Stomach is a wide, J-shaped bag-like organ. Highly muscular walls of the stomach help in churning the food.
  • The stomach has 4 regions: cardiac part, fundus, body and pyloric part.
  • The walls of the stomach secrete hydrochloric acid.
  • It makes the medium inside the stomach acidic.
  • The acidic medium is necessary for gastric enzymes to work.
  • The enzyme pepsin secreted in the stomach; does partial digestion of protein.
  • The mucus secreted by the walls of the stomach saves the inner lining of the stomach from getting damaged from hydrochloric acid.

Functions of Stomach

  • The stomach serves 4 main functions: storage of food, mechanical churning of food, partial digestion, and regulation of the flow of food into the small intestine.

Small Intestine:

  • It is a highly coiled tube-like structure.
  • The small intestine is longer than the large intestine.
  • It is the longest part of the alimentary canal.
  • The small intestine is the site of the complete digestion of carbohydrates, proteins and fats. It receives the secretions of the liver and pancreas for this purpose.
  • The small intestine is divided into three parts, viz. duodenum, jejunum and ileum.


  • Liver is the largest organ in the human body.
  • Liver manufactures bile: which gets stored in gallbladder.


  • Pancreas is situated below the stomach.
  • It secretes pancreatic juice which contains many digestive enzymes.
  • Bile and pancreatic juice go to the duodenum through a hepato-pancreatic duct.
  • Bile breaks down fat into smaller particles.
  • This process is called emulsification of fat.
  • After that, the enzyme lipase digests fat into fatty acids and glycerol.
  • Trypsin and chymotrypsin are enzymes which digest protein into amino acids.
  • Complex carbohydrates are digested into glucose.

Small Intestine

  • The major part of digestion takes place in the duodenum.
  • No digestion takes place in jęjunum.
  • The inner wall in the ileum is projected into numerous finger-like structures; called villi
  • Digested food is absorbed by villi.

Large Intestine:

  • Large intestine is smaller than small intestine.
  • Undigested food goes into the large intestine.
  • Some water and salt are absorbed by the walls of the large intestine.
  • After that, the undigested food goes to the rectum: from where it is expelled out through the anus.
Flow chart of process of Digestion
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