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Blood cells

Red blood cells are biconcave discs of about 7um in diameter. The haemoglobin they contain combines loosely with oxygen which is then transported around the body. Their shape allows the cell to distort and access capillary vessels otherwise too narrow for them to enter. White blood cells defend the body against foreign bodies by engulfing and digesting them.

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Blood clots form when blood is exposed to air and is an effective mechanism that arrests bleeding from a wound. Fibrinogen, a soluble plasma protein, is converted into long strands of insoluble fibrin which entraps blood cells.

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