Composition of Blood

Cells and the plasma

What is blood?

Blood contains different cell types (corpuscles) 45%:

i) mainly red blood cellsii) white blood cells

(Leucocytes)iii) platelets; the fragments

of cells which begin the clotting processplasma (55%)the liquid part and the ions, nutrients and wastes it contains

Red blood cells Carry Oxygen Contain haemoglobin which combines with oxygen to form oxyhaemoglobin (reversible reaction)They don’t have a nucleus so there is more room for haemoglobinAre a biconcave disc, this increases surface area to volume ratio to increase rate of oxygen uptake.They bend as they pass through capillaries

Red Blood cells in capillaries

Capillaries are very narrow.Red blood cells bend as they pass through themThis is an advantage, it keeps them in very close contact with the capillary walls; this reduces the diffusion distance for gas exchange with the surrounding tissues

White blood cells - Lymphocytes

Lymphocytes are the white blood cells which make antibodies to attack bacteria and viruses.They patrol all the blood vessels and also pass into tissue e.g. lung tissueThey are larger than red blood cells and are nucleated.

White blood cells - phagocytes

These engulf bacteria or viruses, usually after they have clumped following antibody attack.Like other white blood cells they are nucleated and larger than red blood cells

Platelets Platelets release an enzyme when exposed to air or fatty deposits This enzyme makes soluble fibrinogen become insoluble fibrin The optimum temperature for the enzyme is 37 degrees centigradeThis helps blood to clot at a wound

Blood ClottingBlood will clot when exposed to air, this will happen when you cut yourself.It can also happen around cholesterol deposits.Blood clots at a wound prevent pathogens from entering the body

Blood Plasma

Questions

1. Urea is found in the plasma, how do you think it is filtered out from the blood? 1 mark2. Explain the advantage to gas exchange of the red blood cells bending as they pass through narrow capillaries. 2 marks3. Sodium chloride in our diet leads to two important ions in our plasma, note these down.2 marks4. Explain how a scab forms at a wound 2 marks5. Explain how oxygen is transported in the blood 2marks