The Digestive System

This lesson covers: 

1. The organs of the alimentary canal
2. The mechanical and chemical breakdown of food

Parts of the alimentary canal

The alimentary canal is the path food travels through during digestion.

1. Mouth - Chewing happens here to break up food. Saliva contains an enzyme, amylase, that starts digesting carbohydrates.
2. Oesophagus - Transports food to the stomach.
3. Stomach - Churns and mixes food. Stomach acid gives the correct conditions for proteases to begin digesting proteins.
4. Liver - Makes alkaline bile to emulsify fats.
5. Pancreas - Produces enzymes to digest carbohydrates, fats, and proteins.
6. Small intestine - Absorbs nutrients from broken down food.
7. Large intestine - Absorbs water.
8. Rectum - Stores undigested waste until it's egested.

Mechanical and chemical digestion

Digestion involves breaking down the food we eat so the nutrients can be absorbed.

This happens in two main steps:

1. Mechanical breakdown - Physically breaking down food into smaller pieces.
2. Chemical breakdown - Chemically breaking down large molecules to small soluble molecules using enzymes.

Mechanical digestion

Mechanical digestion mainly happens in the mouth and stomach:

• Food is chewed and mixed with saliva, which contains mucus to lubricate food and the enzyme amylase.
• In the stomach, muscular contractions churn and mix food with stomach acids and enzymes.

Chemical digestion

Digestive enzymes chemically breakdown food molecules into smaller soluble molecules that can be absorbed.

There are three important digestive enzymes:

1. Amylase - Breaks down carbohydrates.
2. Protease - Breaks down proteins.
3. Lipase - Breaks down fats and lipids.

Bile produced by the liver also emulsifies fats in the small intestine. This involves breaking down fats into smaller pieces for enzymes to act on them.

Where do we find digestive enzymes?

All three of these types of enzyme can be produced by the pancreas and small intestine.