Edexcel iGCSE Biology-2.27 structure and function of the human alimentary canal- Study Notes- New Syllabus

Human Alimentary Canal – Structure & Function

📝 Introduction

The alimentary canal is the long tube running from mouth → anus.
Its job is to digest food into smaller, soluble molecules and absorb them for use in the body.

🧩 Main Parts

1. Mouth

• Structure: Teeth, tongue, salivary glands.
• Functions:
  • Mechanical digestion → teeth break food into smaller pieces → ↑ surface area.
  • Chemical digestion → saliva has amylase → starch → maltose.
  • Tongue mixes food with saliva → forms bolus for swallowing.

2. Oesophagus

• Structure: Muscular tube connecting mouth → stomach.
• Functions: Moves bolus by peristalsis (waves of muscle contraction). No digestion here.

3. Stomach

• Structure: Muscular sac with glands secreting gastric juice.
• Functions:
  • Mechanical digestion → muscles churn food into chyme.
  • Chemical digestion:
    • Pepsin (protease) → proteins → peptides.
    • HCl → kills bacteria + provides acidic pH for pepsin.

4. Small Intestine

• a) Duodenum (first part):
  • Pancreas enzymes:
    • Amylase → starch → maltose
    • Protease → proteins → amino acids
    • Lipase → lipids → fatty acids + glycerol
  • Liver (bile): Neutralises acid + emulsifies fats (↑ surface area for lipase).
  • Digestion of all food groups completed here.
• b) Ileum (second part):
  • Specially adapted for absorption:
  • Long length + villi + microvilli → very large surface area.
  • Thin walls → short diffusion distance.
  • Rich blood supply → maintains concentration gradient.
  • Absorbs glucose, amino acids, fatty acids, glycerol, vitamins, minerals.

5. Large Intestine

• a) Colon: Absorbs water + some minerals → forms semi-solid faeces.
• b) Rectum: Stores faeces before egestion.

6. Pancreas (Accessory organ)

• Produces pancreatic juice with amylase, protease, lipase.
• Secreted into duodenum.

📊 Summary Table

⚡ Quick Recap 
Mouth = chew + amylase.
Oesophagus = peristalsis.
Stomach = churn + pepsin + HCl.
Duodenum = enzymes + bile → finish digestion.
Ileum = villi → absorption.
Colon = water absorption.
Rectum = stores faeces.
Pancreas = enzyme factory.