Digestion

What is Digestion?

Digestion is the process of breaking down large, insoluble molecules into smaller, soluble molecules that can be absorbed into the bloodstream.

💡 Key Concept: Large food molecules cannot be absorbed into the blood, so they must be broken down first.

The Digestive System – Key Organs & Functions

Organ	Function
Mouth	Food is chewed and mixed with saliva (which contains amylase to break down starch).
Oesophagus	Carries food from the mouth to the stomach via peristalsis (wave-like muscle contractions).
Stomach	Contains hydrochloric acid (kills bacteria & provides optimum pH for protease).
Liver	Produces bile, which neutralises stomach acid and emulsifies fats.
Gallbladder	Stores and releases bile into the small intestine.
Pancreas	Produces digestive enzymes (amylase, protease, lipase).
Small Intestine	Enzymes complete digestion and nutrients are absorbed into the bloodstream.
Large Intestine	Absorbs water, forming solid waste (faeces).
Rectum & Anus	Stores and removes waste from the body.

Enzymes in Digestion

Enzyme	What It Breaks Down	Product	Where It Works
Amylase (a carbohydrase)	Starch	Maltose → Glucose	Mouth & Small Intestine
Protease (e.g., Pepsin, Trypsin)	Proteins	Amino Acids	Stomach & Small Intestine
Lipase	Lipids (fats)	Glycerol + Fatty Acids	Small Intestine

💡 Bile is important! It neutralises stomach acid and emulsifies fats, making it easier for lipase to work.

How the Small Intestine is Adapted for Absorption

The small intestine absorbs nutrients into the blood. It is well adapted for this:

✅ Villi & Microvilli – Increase surface area for diffusion.
✅ Thin walls – Short diffusion distance.
✅ Rich blood supply – Maintains concentration gradients.

Questions

What is the role of bile?
Where is amylase produced?
What enzyme breaks down proteins?
How is the small intestine adapted for absorption?
What happens in the large intestine?

Summary

Digestion breaks down large molecules into smaller ones for absorption.
Enzymes like amylase, protease, and lipase help with digestion.
Bile helps by neutralising stomach acid and breaking fats into smaller droplets.
The small intestine is adapted for maximum absorption of nutrients.