Functions of the Blood

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Blood has 4 main components:

1) PlASMA - liquid part of the blood (pale yellow colour), mainly consisting of water. It is essentially the blood without the blood cells. It carries:

- red and white blood cells and platelets

- digested food molecules from the gut to the body cells

- CO2 from the body cells to the lungs

- Urea from the liver to the kidneys

- Hormones which act as chemical messengers

- Heat energy

2) PLATELETS - help clot the blood by "clumping" together.

- stops blood loss and also prevents microorganisms entering the wound (infection)

- in a clot, platelets are held together by a mesh of a protein called "fibrin".

3) RED BLOOD CELLS - adapted to carry O2 around the body. The O2 molecule attaches to the haemoglobin protein which the red blood cells are filled with. This is how they're adapted:

- small and have a biconcave shape to give a large surface area for absorbing and releasing oxygen

- contain haemoglobin (gives blood its colour) - it contains a lot of iron. In the lungs, the oxygen reacts with the haemoglobin to form oxyhaemoglobin. In body cells, the reverse reaction happens to release oxygen into the


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