Blood
Blood is made up of a liquid called plasma.
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Cells are also carried in the plasma. They are adapted for different jobs. Red blood cells are shaped like a biconcave disc. They contain haemoglobin which can carry oxygen around the body.
The shape of red blood cells does not allow them to carry more oxygen, but the increased surface area to volume ratio lets them gain or lose it quicker.
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In the tissues the reverse of this reaction happens and oxygen is released:
haemoglobin + oxygen = oxyhaemoglobin
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The blood is carried around the body in arteries, veins and capillaries.
| Arteries | Veins | Capillaries |
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Carry blood away from the heart |
Carry blood back to the heart |
Join arteries to veins. |
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Have thick, muscular walls because the blood is under high pressure. |
Have valves and a wide lumen because the blood is under low pressure.
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Have permeable walls so that substances can pass in and out to the tissues.
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You need to remember arteries carry blood away from the heart and veINs back INto the heart.
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