Digestion and Absorption

As we have learned, digestion is the simple process of breaking down food molecules into smaller components. This process begins from the mouth and is then carried on to the stomach, to the small intestine, large intestine and then to the anus. This is the physical process of digestion. Here, let us learn more in detail about the chemical process of digestion involved while digesting biomolecules.

Table of Contents

What is Digestion?

What is Absorption?

Digestion and Absorption of Carbohydrates

Digestion and Absorption of Proteins

Digestion and Absorption of Lipids

Frequently Asked Questions

What is Digestion?

Digestion is the process of breaking large, insoluble food molecules into smaller molecules for absorption into the bloodstream. This process involves the use of many digestive fluids and enzymes such as saliva, mucus, bile and hydrochloric acid, among others.

There are four primary stages of food digestion in the human body that include:

  • After the intake of food through the mouth, it makes its way through the stomach into the small intestine, where it is digested.
  • The nutrients from the digested food get absorbed into the bloodstream through small pores in the small intestine.
  • The remaining undigested food is sent to the large intestine, where any unprocessed water or nutrients are reabsorbed into the body.
  • The remaining waste food product is passed out of the body in the form of stools.

What is Absorption?

Absorption is the process of the absorbing or assimilating substances into the cells or across the tissues and organs through the process of diffusion or osmosis. Also refer: Difference between Osmosis and Diffusion

Digestion and Absorption of Carbohydrates

Digestion and Absorption of Carbohydrates-Flowchart

Carbohydrates are one of the essential nutrients in the human diet. There are two types of carbohydrates that can be digested by the human digestive system– sugar and starch.

Sugar is broken down in the gastrointestinal tract by the small intestine and three enzymes present in the mouth, namely, Lactase, Sucrase, and Maltase.

Digestion and Absorption of CarbohydratesIn the same way, starch is broken down with the help of the Amylase enzymes which are present in the mouth and the stomach. After digestion, carbohydrates are absorbed in the small intestine with the help of minute finger-shaped projections known as Villi. Also refer: Carbohydrates
The chemical digestion of carbohydrates begins in the mouth. The below flowchart explains in detail about the series of steps involved in breaking down the carbohydrates into their monomers.

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Digestion and Absorption of Proteins

Digestion and Absorption of Proteins-FlowchartProteins play a vital role in the growth and replenishment of body cells and tissues. The digestion of proteins takes place in the stomach with the help of protease and pepsin enzymes, which breaks down the proteins into amino acids. The process is facilitated by the hydrochloric acid present in the stomach. Amino acids are tiny elements which get absorbed into the blood system through the wall of the small intestine. Also refer: Proteins

Digestion and Absorption of Lipids

Lipids are organic compounds comprising fatty acids, which are insoluble in water. Fats are the most common examples of lipids. The insoluble property of lipids makes the digestion and absorption of fats a complicated process.

Since they are hydrophobic, fats stick together as a large glob of insoluble mass after reaching the stomach. It is broken down with the help of bile juice, which contains bile salts. These broken molecules are then acted upon by pancreatic lipase, the major fat-absorbing enzymes in the body.

Digestion and Absorption of Lipids

Pancreatic lipase breaks down fats into tiny molecules of free fatty acids and monoglycerides, which are small enough for the small intestine to push through into the bloodstream.

Also refer: Lipids

For more detailed information about Digestion and Absorption, its process or any other related topics and for digestion and absorption class 11 revision notes explore @ BYJU’S Biology.

Frequently Asked Questions


What is protein digestion?

Protein is one of the essential compounds in our body. Human saliva contains the enzymes lipase and amylase. They mainly digest fats and carbohydrates. As soon as we start chewing, protein digestion begins. Protein digestion first breaks the complex molecule into peptides containing various amino acids and then into individual amino acids.


Where does protein digestion begin and end?

Protein digestion begins when you first start chewing and concludes in the small intestine. To produce more proteins, the body reuses amino acids.


Digestion of both starch and protein is done by ___________.

Digestion of both starch and protein is done by the pancreatic juice. The pancreatic enzymes include lipase, which breaks down triglycerides into fatty acids and monoglycerides. Trypsin, chymotrypsin, and elastase all break down proteins. Amylase breaks down the excess complex carbohydrates into monosaccharides. Therefore, the digestion of carbohydrates, protein, and fat is unattainable without the pancreas.


How are proteins in your food digested?

Proteins undergo hydrolysis, which converts them into amino acids, during digestion. The amino acids are dissolved in our blood and transported to organs and tissues. The amino acids are either converted into energy or put together into proteins using condensation polymerization.


How are proteins digested in small intestine?

The partially digested meal, or chyme, next passes into the small intestine, where intestinal fluids and pancreatic enzymes exist. The pancreatic juices and intestinal secretions induce several chemical reactions. These include the enzymes chymotrypsin, trypsin, and elastase, which break down the protein into smaller peptides. Carboxypeptidase, aminopeptidase, and dipeptidase break down the peptides into free amino acids, which can then enter the bloodstream. The pepsin enzyme dissolves peptide bonds and helps in the initial stages of protein digestion in the stomach.

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