Blood transports materials and distributes heat around the body. It also helps to protect against disease. Blood contains plasma, which is a liquid that cells and cell fragments are suspended in.
Plasma is a straw-coloured liquid that makes up just over half the volume of blood.
Types of blood cell and cell fragments:
This table explains the functions of various blood components.
|Plasma||Transporting other components such as carbon dioxide, digested food molecules, urea and hormones. Distributing heat.|
|Red blood cells||Transporting oxygen|
|White blood cells||Ingesting pathogens and producing antibodies|
|Platelets||Involved in blood clotting|
Red blood cells transport the oxygen required for aerobic respiration in body cells.
They must be able to absorb oxygen in the lungs, pass through narrow blood capillaries and release this oxygen to respiring cells.
Red blood cells have adaptations that enable them to carry a maximum amount of oxygen:
There are several main types of white blood cell.
About 70 per cent of white blood cells are phagocytes. Phagocytes engulf and digest unwanted microorganisms that enter the blood, by the process of phagocytosis. They are part of the body's immune system.
Lymphocytes make up about 25 per cent of white blood cells. They are also part of the body's immune system. Lymphocytes produce soluble proteins called antibodies and antitoxins when a foreign body such as a microorganism enters the body.
Platelets are cell fragments produced by giant cells in the bone marrow.
Platelets stop bleeding in two main ways: