Edexcel iGCSE Biology-3.18 Structure & Function of structure of arteries, veins and capillaries- Study Notes- New Syllabus

Blood Vessels: Structure & Function

📝 Introduction

The circulatory system has three main types of blood vessels:

• Arteries → carry blood away from the heart.
• Veins → carry blood towards the heart.
• Capillaries → allow exchange of substances between blood and tissues.

🚀 Arteries

Function: Carry blood away from the heart (usually oxygenated, except pulmonary artery).

• Thick muscular walls → withstand high pressure from heart pumping.
• Elastic fibres → allow walls to stretch & recoil as blood pulses.
• Small lumen → maintains high pressure.
• No valves (except at the heart).

🔄 Veins

Function: Carry blood back to the heart (usually deoxygenated, except pulmonary vein).

• Thinner walls → blood under low pressure.
• Large lumen → reduces resistance to flow.
• Valves present → prevent backflow of blood.
• Blood flow helped by skeletal muscle contraction (muscle pump).

🌱 Capillaries

Function: Site of exchange of substances (O₂, CO₂, nutrients, waste) between blood & body cells.

• Very thin walls (one cell thick) → short diffusion distance.
• Narrow lumen → blood flows slowly, allows time for exchange.
• Found in large networks → increase surface area for diffusion.

📊 Comparison Table

⚡ Quick Recap
Arteries: Thick walls, small lumen → carry blood at high pressure.
Veins: Thin walls, wide lumen, valves → carry blood at low pressure, prevent backflow.
Capillaries: One cell thick, large network → efficient exchange of materials.