Overview of Chemical Digestion

Chemical digestion is the process by which large, complex food molecules are broken down into smaller, simpler molecules that can be absorbed by the body.
It involves specific enzymes that catalyse the breakdown of specific types of food:
- Carbohydrases break down carbohydrates.
- Proteases break down proteins.
- Lipases break down fats.
These processes occur at different stages along the alimentary canal, in slightly different ways, facilitated by different environments.

Digestion in the Mouth

The process of chemical digestion begins in the mouth with the enzyme amylase, found in saliva.
Amylase begins breaking down starch, a complex carbohydrate, into smaller molecules of maltose, a simpler sugar.

In the stomach, the enzyme pepsin is responsible for commencing protein digestion.
Pepsin works best in acidic conditions, enabled by the secretion of hydrochloric acid in the stomach which provides a low pH environment.

The small intestine is where most of the chemical digestion occurs, involving a number of different enzymes.
Pancreatic juice, secreted by the pancreas into the small intestine, contains a mixture of different enzymes:
- Amylase continues the digestion of starch into maltose.
- Trypsin and chymotrypsin (proteases) continue breaking down proteins into peptides.
- Lipase starts the breakdown of fats into fatty acids and glycerol.
Intestinal juice, secreted by the lining of the small intestine, also contains more enzymes:
- Maltase, sucrase and lactase (all carbohydrases) break down maltose, sucrose and lactose respectively into simple sugars ready for absorption.
- Peptidases break the peptides (from protein digestion) into amino acids.

Understanding the mechanisms of chemical digestion helps comprehend how our bodies extract the vital nutrients required from the food we consume.
It’s paramount to know the role and specificity of enzymes in this process, alongside the different environments needed for optimal enzyme action.