Process of Digestion

Learning Objectives:

At the end of this session, you will be able to know about

  • Digestion process
  • Steps involved in absorption process
  • Steps involved in metabolic pathway
  • Site of storage

Lesson Plan:


          Carbohydrates is an important sources energy to the body. Dietary carbohydrates consist of Polysaccharides, Disaccharides and monosaccharides. Only monosaccharides could be absorbed into the blood stream. Through digestion process complex carbohydrates are converted into simple sugars.

The Process of Digestion:

          Digestion of food is the break down of larger molecules into smaller molecules through mechanical and chemical process.

          Different organs in the Gastrointestinal tract work together in the process of digestion.


          While we talk about carbohydrates, the first stage of digestion begins in the mouth. During mastication or chewing the food, saliva gets secreted along with an enzyme called salivary amylase otherwise called as Ptyalin, which converts starch into dextrin and maltose.  

Though it is an initial process which has begun in the mouth, salivary amylase does not have much impact to the complex starch to get digested fully.


After mastication, carbohydrates along with salivary amylase passes to the stomach through esophagus, where the salivary amylase gets inactivated due to the gastric acid.

In the stomach, the digestion process continues with acidic gastric juice and enzyme. Semi-solid mass of food along with the secretions from pancreas, liver and gall bladder are known as chyme.

Next process happens in the duodenum, the first segment of the small intestine, where pancreatic juices contains pancreatic amylase mixes with the chyme which completes the break down of starch and glycogen into disaccharides called maltose, sucrose and lactose.  

 Brush border enzymes found on the microvilli of the small intestine such as maltase, iso-maltase, sucrase and lactase catalyze the reaction, converts disaccharides into monosaccharides i.e. glucose, fructose and galactose.

          Indigestible fibers and starch e.g. cellulose, hemicellulose, pentosans and galactans etc., which are not digested in the small intestine passes into the large intestine, where the indigestible fibers are digested by colonic bacteria releases short chain fatty acids (SCFA) such as acetate, butyrate and Propionate.

The short chain fatty acids are absorbed across the gut epithelium and pass through the portal vein to the liver for metabolism.