The circulatory system has three main components:
It has two main functions:
The main blood components are:
|Red blood cell||Carry oxygen.||Contain haemoglobin (rich in iron) to carry oxygen. Biconcave shape to provide a large surface area for the diffusion of oxygen. No nucleus to provide more space for haemoglobin.|
|White blood cell||Defend the body against disease.||Large cells that contain a nucleus. There are 2 types: Lymphocytes – make antibodies. Phagocytes – engulf and digest microorganisms.|
|Platelets||Convert fibrinogen to fibrin. Fibrin forms a mesh that traps blood. Important in blood clotting and scab formation.||Cell fragments (very small).|
|Plasma||Transports blood cells, digested food molecules (e.g. glucose), carbon dioxide, urea and hormones.||Straw coloured liquid.|
If red blood cells are placed in a high concentration of water, osmosis will cause water to move into the cell and, without a cell wall, they will lyse (burst).
Salts and other chemicals are present in the blood plasma to keep its concentration similar to the concentration of the blood cells.