1.4 Chemical Digestion

Introduction

Food is broken down in two ways: mechanically (by chewing, churning, and grinding) and chemically (by enzymes). Chemical digestion is the process in which large food molecules are broken down into small soluble molecules with the help of enzymes. This topic introduces the overall process of chemical digestion and explains how it occurs in different regions of the alimentary canal.

Definition

Chemical digestion is the breakdown of large food molecules into small soluble food molecules with the help of enzymes.

In simple words, chemical digestion is the use of enzymes to break chemical bonds in food, changing large molecules into small ones that the body can absorb.

Main Idea

Chemical digestion occurs in different regions of the alimentary canal:

• Oral cavity — starch digestion begins
• Stomach — protein digestion begins
• Small intestine — all three major nutrients (carbohydrates, proteins, fats) are digested

Each region has specific enzymes that work on specific substrates. The products of chemical digestion are small molecules that can be absorbed into the blood.

Core Concept

Enzymes in Chemical Digestion

Enzymes are biological catalysts that speed up chemical reactions. In digestion, enzymes break down large food molecules into smaller ones.