Functions
The circulatory system has three main components:
- Blood
- Blood vessels
- The heart
It has two main functions:
- Transportation of substances
- Protection against disease
Blood components
The main blood components are:
| Component | Function | Structure |
| 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. | Yellow coloured liquid. |
| Component | Red blood cell |
|---|---|
| Function | Carry oxygen. |
| Structure | 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. |
| Component | White blood cell |
|---|---|
| Function | Defend the body against disease. |
| Structure | Large cells that contain a nucleus. There are 2 types: Lymphocytes – make antibodies. Phagocytes – engulf and digest microorganisms. |
| Component | Platelets |
|---|---|
| Function | Convert fibrinogen to fibrin. Fibrin forms a mesh that traps blood. Important in blood clotting and scab formation. |
| Structure | Cell fragments (very small). |
| Component | Plasma |
|---|---|
| Function | Transports blood cells, digested food molecules (e.g. glucose), carbon dioxide, urea and hormones. |
| Structure | Yellow coloured liquid. |
Cell lysis
If red blood cells are placed in a high concentration of water, The process by which water moves in and out of cells from a high concentration to a low concentration. 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 The liquid part of the blood containing useful things like glucose, amino acids, minerals, vitamins (nutrients) and hormones, as well as waste materials such as urea. to keep its concentration similar to the concentration of the blood cells.