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Why humans need a circulatory system
- Small surface area compared to volume large diffusion path diffusion alone=too slow
- More active than smaller organisms greater oxygen, etc., requirements
- Pump blood oxygen and glucose to cells cells respire

The double circulatory system
- When blood pumped around body, goes…

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Feature RBC WBC- lymphocytes WBC- phagocytes Platelets

Fragments of other
Biconcave, disc- Large nucleus Lobed nucleus
like (more SA)
Where is/are they Bone marrow Bone marrow
Nucleus? No Yes No
Function Transport oxygen Produce Engulf bacteria + Release chemicals
in form of antibodies to other microbes that…

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Blood clotting
1. Blood vessel damaged (smooth walls rough edges)
2. Damaged tissue releases chemicals + platelets bump into rough edges
3. Prothrombin (soluble) thrombin (enzyme)
4. Thrombin acts on fibrinogen (soluble) fibrin (insoluble)
5. Fibrin fibre mesh across wound
6. RBCs and platelets trapped in mesh, forming clot


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- Blood needs to be pumped faster
- Heart rate and stroke volume must increase
- Carbon dioxide and lactic acid also removed from muscles as a result

Effects of smoking on heart
- Blockage or narrowing of arteries (incl. Coronary) as stimulates deposition of cholesterol in vessels
increased blood…

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