GCSE Biology · Edexcel 1BI0 · Topic 8B
Blood and the circulatory system
Key points
- Blood components: red blood cells (haemoglobin, no nucleus, biconcave shape to carry oxygen), white blood cells (defence), platelets (clotting) and plasma (carries glucose, CO₂, urea and hormones).
- Arteries carry blood away from the heart at high pressure: thick muscular, elastic walls. Veins carry blood back at low pressure: thinner walls, wide lumen, valves. Capillaries are one cell thick for exchange.
- The heart has four chambers. Deoxygenated blood: vena cava → right atrium → right ventricle → pulmonary artery → lungs. Oxygenated blood: pulmonary vein → left atrium → left ventricle → aorta → body.
- The left ventricle wall is thicker because it pumps blood around the whole body. Valves stop backflow.
- Cardiac output = stroke volume × heart rate.
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The circulatory system is the body's delivery network. This sub-topic covers what blood is made of, how the three types of blood vessel are adapted, the route blood takes through the heart and how to calculate cardiac output.
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