Blood transports materials and distributes heat around the body. It also helps to protect against disease. Blood contains plasma, which is a liquid that the other components of blood are suspended in.
Plasma is a straw-coloured liquid that makes up just over half the volume of blood.
This table explains the functions of various blood components.
|Plasma||Transporting dissolved 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 have several adaptations that enable them to carry out this function:
There are several types of white blood cell.
Lymphocytes make up about 25 per cent of white blood cells. Lymphocytes produce soluble proteins called antibodies when a foreign body such as a microorganism enters the body.
Antibodies neutralise pathogens in a number of ways:
Lymphocytes may also release antitoxins that stick to the toxins that the microorganism makes, which stops it damaging the body.
Both phagocytes and lymphocytes are part of the body's immune system.
Platelets are cell fragments produced by giant cells in the bone marrow.
Platelets stop bleeding in two main ways: