Food is one of the most basic requirements of all living organisms as it provides us the energy for growth and tissue repairing. The major components of our food are proteins, fats, and carbohydrates. Whereas, vitamins and minerals are required in small quantities.

  • Biomacromolecules present in food cannot be used in their original form by our body, so they have to be broken down and converted into simpler substances through the digestive system. This process is known as digestion carried by our digestive system by mechanical and biochemical methods.
  • The human digestive system comprises of the alimentary canal and the associated glands – The alimentary canal begins with the mouth and opens through the anus.
  • The mouth has several teeth and a muscular tongue. The hard chewing surface of the teeth is made up of enamel which helps in the mastication of food.
  • The tongue has small projections called papillae, which bear taste buds.
  • The mouth leads into a short pharynx which serves as a common passage for food and air.
  • The esophagus is a thin and long tube that leads to a ‘J’ shaped bag-like structure called the stomach. The stomach has 4 major parts – cardiac, fundic, body, and pyloric.
  • The pyloric part opens into the duodenum (the first part of the small intestine).
  • The ileum (the last part of the small intestine) opens into the large intestine, and then it opens into the anus.
  • The digestive glands related to the alimentary canal are comprised of salivary glands, the liver, and the pancreas.



The process of digestion is followed by mechanical and chemical processes.

  • The buccal cavity enacts two major functions – mastication of food and facilitation of swallowing.
  • Mucus in saliva helps in lubricating and adhering the masticated food into a bolus.
  • The bolus then moves into the pharynx and then into the esophagus by swallowing.
  • The chemical process of digestion begins in the oral cavity by the hydrolytic action of the carbohydrate-splitting enzyme, the salivary amylase.
  • The stomach stores food for about 4-5 hours.
  • The food in the stomach mixes rigorously with the acidic gastric juice of the stomach by churning movements of its muscular wall and it is called chyme.
  • Then the breakdown of macromolecules takes place in the duodenum region of the small intestine.
  • The simpler substances thus formed are absorbed in the jejunum and ileum regions of the small intestine.
  • The undigested and unabsorbed substances are passed on to the large intestine.
  • These undigested substances called feces enter into the caecum of the large intestine. It is temporarily stored in the rectum till defaecation.


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