Science Notes on Human Digestive System, Read Here

By Neha Joshi|Updated : February 27th, 2020

This article comprises detailed study notes on the topic of the human digestive system. Questions on this topic are generally asked in the REETUPTETCTET and other teaching examinations. 

Digestive systems are one of the vital topics asked in teaching exams. Here, in this article, we are going to have a discussion on the human digestive system. Various organs, enzymes, glands, enzymes etc. Play an important and specific role in the process of digestion. The more notable fact is that digestion starts from the mouth, not from the stomach. In this article, we will discuss amazing facts, relevant information and a lot more from an exam point of view.

Digestive System:

A digestive system is a group of organs which work to convert food into basic nutrients for feeding energy to the whole body. Human does not produce their own food like plants and depend on other plants and animals for food, hence called Heterotroph. Human needs various nutrients, proteins and vitamins which are derived from food through digestion. Chewing, in which food is mixed with saliva begins the process of digestion. This produces a bolus which can be swallowed down the oesophagus and into the stomach. The complete process of nutrition is divided into five stages:

  • Ingestion
  • Digestion
  • Absorption
  • Assimilation
  • Defecation


The process of taking food, drink or any other substance into the body by swallowing and absorbing it, is known as Ingestion.


  • The digestive system contains six components which are as follows-
  1. Mouth
  2. Oesophagus
  • Stomach
  1. The small intestine
  2. Colon (large intestine)
  3. Rectum
  • Digestion is a process through the large insoluble and non-absorbable food particles are broken down into smaller water-soluble and absorbable particles which are finally absorbed by blood plasma.
  • It is a form of catabolism which is divided into two groups based on how food is broken down in the body, if food is broken down through mechanical means then it is known as Mechanical Digestion and if it is through chemical means then it is called Chemical Digestion.

Mouth and Oesophagus

  • Digestion initiates right from the mouth, where the Salivary gland secrets the Saliva in the mouth in which two types of enzymes are found, ptyalin and maltase.
  • saliva contains an enzyme called salivary amylase that begins the process of converting starches in the food into maltose
  • Around 1.5 litres of saliva is secreted in humans on an average day, it is acidic in nature (pH 6.8)
  • Through a food pipe or Oesophagus, food reaches into the stomach.

Digestion in Stomach:

  • The ph of the stomach is 1.5-2.5. This acidic environment helps in breaking the food particle and absorption of necessary nutrients from food.
  • The highly acidic environment of the stomach contains gastric glands which secrete gastric juice, this is a light yellow acidic acid.
  • Pepsin and Renin are the enzymes in gastric juice.
  • Parietal cells secrete Chlorine and Hydrogen ions which combine to form Hydrochloric acid which helps in killing microorganisms and with the help of the enzyme pepsin helps in the hydrolysis of proteins.
  • Hydrochloric acid makes the food acidic by which the ptyalin reaction of the saliva end.
  • Pepsin breaks down the protein into peptones and Renin breaks down the Caseinogen into Casein.

Digestion in Duodenum:

  • The duodenum is the first and shortest segment of the small intestine. It receives partially digested food (known as chyme) from the stomach and plays a vital role in the chemical digestion of chyme in preparation for absorption in the small intestine.
  •  The gall bladder releases bile, which has been produced by the liver, to help further break fats down into a form that can be absorbed by the intestines.
  • As the food reaches the duodenum bile juice from the liver combines with it. The main function of the bile juice is to convert the acidic food into alkaline, as it is alkaline in nature.
  • Pancreatic juice from the pancreas combines with food and it contains the following enzymes:
  1. Trypsin: It converts the protein and peptone into polypeptides and amino acids.
  2. Amylase: It converts the starch into soluble sugar.
  3. Lipase: It converts emulsified fats into glycerol and fatty acids.

Digestion in Small Intestine:

  • Here the process of digestion is completed and absorption of digested foods starts.
  • In the small intestine, intestinal juices secrete and it is alkaline in nature and around 2 litres of intestinal juice secretes per day.
  • Intestinal juice contains the following enzymes:
  1. Erepsin: It converts the remaining protein and peptone into amino acids.
  2. Maltase: It converts maltose into glucose.
  3. Sucrase: It converts the sucrose into glucose and fructose.
  4. Lactase: It converts lactose into glucose and galactose.
  5. Lipase: It converts emulsified fats into glycerol and fatty acids.


  • Digested food is absorbed by blood plasma is known as Absorption.
  • The absorption of digested foods takes place through small intestine villi which are finger-like structures extended into the lumen of the small intestine.


  • The use of absorbed food in the body or movement of digested particles where they are used is called assimilation


  • It is the final act of digestion. It is also known as a bowel movement. Undigested food reaches from the small to the large intestine where bacterias convert it into faeces which are excreted through the anus.

Disorders of the digestive system:

Here are some important digestive disorders in human beings.




Expulsion of food from the mouth due to irritation in the stomach.


Infectious disease resulting in a loose frequent bowel.


Yellow colouration of the skin and mucous membrane.

Gall stone

Cholesterol crystallises to form gall stone.


the difficulty of defecation due to decreased mobility in the large intestine.

That's it from our side! Read the above-given article and boost your preparation for the upcoming examination.




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