Blood and the Circulatory SystemAQA GCSE Biology: Revision notes
Section 1
How does the heart pump blood around the body?
The human heart is a double circulatory system:
- The right ventricle pumps deoxygenated blood to the lungs for gas exchange
- The left ventricle pumps oxygenated blood around the rest of the body
Major blood vessels connected to the heart: aorta (oxygenated blood out to the body), vena cava (deoxygenated blood in from the body), pulmonary artery (deoxygenated blood out to the lungs), pulmonary vein (oxygenated blood in from the lungs), and coronary arteries (supply the heart muscle itself with blood).
Section 2
What controls heart rate?
The natural resting heart rate is controlled by a group of cells in the right atrium called the pacemaker.
Artificial pacemakers are electrical devices implanted to correct irregularities in heart rate, delivering small electrical impulses to keep the heart beating regularly.
Section 3
How are the three blood vessels adapted to their function?
| Vessel | Function | Key adaptation |
|---|---|---|
| Artery | Carries blood away from the heart, usually at high pressure | Thick, muscular, elastic walls to withstand high pressure |
| Vein | Carries blood back to the heart, at low pressure | Wide lumen and valves to prevent backflow |
| Capillary | Exchanges substances with tissues | Walls one cell thick, for a short diffusion path |
Section 4
What are the components of blood?
Blood is a tissue made of plasma in which cells are suspended:
- Plasma — the liquid part; transports dissolved substances such as carbon dioxide, digested food, urea and hormones
- Red blood cells — contain haemoglobin and carry oxygen; have no nucleus and a biconcave disc shape to maximise surface area for gas exchange
- White blood cells — defend against pathogens (phagocytosis and antibody production); have a nucleus
- Platelets — small cell fragments that help blood clot at wounds
Section 5
What can go wrong with the heart, and how is it treated?
- Coronary heart disease: fatty material builds up inside the coronary arteries, narrowing them and reducing blood flow to the heart muscle, which can cause a heart attack. Stents hold coronary arteries open; statins reduce blood cholesterol, slowing further fatty deposit
- Faulty heart valves may not open fully or may leak; they can be replaced with biological or mechanical valves
- Severe heart failure may require a donor heart, a heart and lung transplant, or an artificial heart (often used temporarily while a patient waits for a transplant)
Each treatment has advantages and disadvantages: drugs are non-invasive but must be taken long-term; mechanical devices act immediately but carry surgical risk and may wear out; transplants can fail due to rejection and donor organs are in short supply.
For evaluate questions, always give a point for AND against each treatment option, not just facts about how it works.
Must Know
- The heart is a double circulatory system: right side → lungs, left side → body
- Vessels: aorta, vena cava, pulmonary artery, pulmonary vein, coronary arteries
- Heart rate is controlled by the pacemaker in the right atrium
- Arteries (thick/elastic), veins (wide lumen/valves), capillaries (one cell thick) are each adapted to their function
- Blood = plasma + red blood cells (oxygen) + white blood cells (defence) + platelets (clotting)
- Coronary heart disease narrows coronary arteries; treated with stents or statins, or in severe cases valve replacement/transplant/artificial heart
That's the notes covered.
Carry on to the next subtopic.