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   The various parts of human digestive system are:


The Digestion in Humans starts with the Ingestion of food. Ingestion means ‘taking in’ - food is taken in by the person, and it reaches the mouth.

(1) Mouth:

The mouth or buccal cavity contains teeth, tongue and salivary glands.


  • Teeth:

The teeth are used to chew the food and break it into smaller pieces so that it is digested easily.

  • Tongue:

The tongue then moves the food around the mouth properly so as to mix food with the saliva.  

  • Salivary Glands:

The salivary glands secrete saliva

  • It contains salivary amylase , an enzyme which helps in the chemical digestion of starch. 
  • Enzymes are biological substances that help in the progress of the reaction.


(2) Oesophagus:

It is also known as the food pipe .

  • From the mouth, the food is pushed into the food pipe (oesophagus) with the action of the tongue. 
  • The walls of the oesophagus contract and expand to help the food move down the pipe into the stomach. This expansion and contraction movement is called Peristalsis. 


(3) Stomach:

Due to the peristaltic movements of oesophagus, the food enters the stomach where a variety of juices act on it. 

  • The food is churned in the stomach for about 3-4 hours where a semi-solid paste is formed. 
  • The stomach wall contains three tubular glands in it. The glands present in this wall of stomach secrete gastric juices
  • The gastric juice contains hydrochloric acid , enzyme pepsin and mucus .


  • Hydrochloric acid: 

  • It kills any bacteria which may enter the stomach along with food.
  • Turns the gastric juice acidic in nature.


  • Pepsin:

  • The enzyme pepsin works in this acidic medium to digest the protein present in the food to convert it into smaller molecules. 
  • This protein digestion begins in the stomach.


  • Mucus:

  • Mucus helps protect the lining of the stomach from the acidic secretion of HCl. 
  • If mucus is not secreted the lining of the stomach will be degraded leading to formation of ulcers.


(4) Small Intestine:

This partially digested food in the stomach now moves forward into the small intestine .

  • The exit of food from the stomach is regulated by sphincter muscle which releases it in small amounts into the small intestine.
  • The small intestine is the largest part of the alimentary canal. It is called the small intestine because it is very narrow
  • The small intestine receives secretions of two glands : liver and pancreas.


  • Liver : 

  • The liver secretes bile juice which is normally stored in the gallbladder and is a greenish yellow liquid .
  • Bile performs two functions :
  • It provides an alkaline medium for the acidic food coming from the stomach for the pancreatic enzymes to act on it
  • Bile salts break down the fats present in food into smaller globules making it easy for the pancreatic enzymes to act and digest them.


  • Pancreas : 

  • Pancreas secrete pancreatic juices which contain digestive enzymes like pancreatic amylase, trypsin and lipase.
  • The enzyme amylase breaks down starch
  • The enzyme trypsin digests proteins
  • The enzyme lipase breaks down emulsified fats .


  • The enzymes present in the intestinal juice complete the digestion of complex carbohydrates into glucose , proteins into amino acids and fats into fatty acids and glycerol
  • After digestion the molecules of food become very small and can then be absorbed by the walls of the small intestine and move further into our blood.
  • The small intestine is the region for absorption of digested food because of the presence of villi
  • Villi are small fingerlike projections which increase the surface area of the small intestine thereby increasing the rate of absorption.

  • From the bloodstream,  the digested food reaches all parts of the body where it becomes assimilated as part of cells.
  • The digested food which is not used by our body immediately is stored in the form of a carbohydrate called glycogen in our liver.


(5) Large Intestine: 

The undigested food passes from the small intestine into a wider tube called the large intestine.


  • Here, most of the water gets absorbed from the undigested food and thus the leftover part becomes almost solid. The solid waste is excreted through the anus as faeces or stool.  
  • The exit of the waste is called egestion or defecation. It is controlled by the anal sphincter.


Dental Caries: 


  • Dental Caries or tooth decay is the damage that occurs to teeth which can potentially result in cavities, dental abscesses or even tooth loss .
  • This begins as a result of plaque deposition on teeth. Plaque is a sticky deposit on teeth in which bacterial growth happens fast. 
  • This bacterial multiplication can convert the sugars in our food to acid. 
  • Enamel is the outermost, hard, white layer of a tooth

This acid may cause enamel deterioration.


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CA Maninder Singh is a Chartered Accountant for the past 12 years and a teacher from the past 16 years. He teaches Science, Accounts and English at Teachoo