Digestion in Intestine



Carbohydrate digestion in small intestine

1. Digestion of most of the nutrients takes place in the duodenum under the action of various enzymes.
2. The pancreatic juice contains starch digesting enzyme called amylase which converts starch into maltose, isomaltose and dextrins.
3. Intestinal juice contains maltase, isomaltase, sucrase, lactase and dextrinase which act as follows:
Maltose = Glucose + Glucose
Isomaltose = Glucose + Glucose
Sucrose = Glucose + Fructose
Lactose = Glucose + Galactose
Dextrins = Glucose


Protein digestion in small intestine

1. Pancreatic juice contains proenzymes trypsinogen, chymotrypsinogen and procarboxypeptidase and enzyme elastase.
2. The bile provides an alkaline medium for various reactions.
3. The intestinal juice contains aminopeptidases and dipeptidases, and enterokinase or enteropeptidase.  
4. Out of these enterokinase activates the trypsinogen. Aminopeptidase hydrolyses the terminal amino group from peptide bonds to release the last amino acid from the peptides thus making the peptide shorter. 
5. Dipeptidase acts on dipeptides to release the individual amino acids.


Digestion of fats

1. Bile juice contains bile salts, which are secreted by the liver in the bile. Bile salts break down the bigger molecules of fat globules into smaller droplets by reducing the surface tension of fat droplets. This process is known as emulsification of fats.
2. Lipase is the enzyme that acts on emulsified fats. It is present both in the pancreatic juice and intestinal juice.
3. Lipase converts emulsified fats into diglycerides and monoglycerides releasing fatty acids at each step.
4. At the end of digestion, all fats are converted into fatty acids, glycerol and monoglycerides.