The Human Heart and Blood Vessels — AQA GCSE Biology
The heart pumps blood around the body in a double circulatory system, through three types of blood vessel.
The double circulatory system
Humans have a double circulatory system — two loops:
- one carries deoxygenated blood from the heart to the lungs and back,
- the other carries oxygenated blood from the heart to the rest of the body and back.
This keeps oxygenated and deoxygenated blood separate and maintains a high pressure to the body.
The heart
- The right side pumps deoxygenated blood to the lungs.
- The left side pumps oxygenated blood around the body — its wall is thicker because it pumps at a higher pressure.
- The natural resting heart rate is controlled by a group of cells (the pacemaker) in the right atrium; artificial pacemakers can correct an irregular rhythm.
The blood vessels
| Vessel | Function | Adaptation |
|---|---|---|
| Artery | carries blood away from the heart | thick, elastic, muscular walls (high pressure) |
| Vein | carries blood back to the heart | thinner walls, large lumen, valves prevent backflow |
| Capillary | exchange of substances with tissues | walls one cell thick, narrow |
Exam tips
- Explain why the left ventricle wall is thicker (pumps blood further, at higher pressure).
- Match each vessel to its function and adaptation.
- Veins have valves; capillaries are one cell thick for efficient exchange.
- Remember the right side handles deoxygenated blood (to the lungs), left side oxygenated (to the body).