Blood is made up of four components, which each perform a different function:
- red blood cells – these carry oxygen around the body and remove carbon dioxide
- white blood cells – these help the body fight infection
- platelets – these tiny cell fragments help the blood to clot (thicken)
- plasma – this yellow fluid transports blood cells and platelets around the body and contains a number of substances, including proteins
Plasma
Plasma is the largest component of blood, making up about 55% of its overall content. It is mainly made up of water and surrounds the blood cells, carrying them around the body.
Plasma also stores body fluids, helps maintain blood pressure and regulates body temperature. It contains a complex mix of substances that are used by the body to perform important functions. These substances include:
- minerals
- salts
- proteins
- hormones (powerful chemicals)
Three important proteins are found in plasma:
- albumin
- clotting (coagulation) factors
- immunoglobulins
These are described in more detail below.
Albumin
Albumin cleans the blood, carries substances around the body and helps to maintain the correct amount of fluid circulating in the body.
Human albumin solution can be used as a treatment to help people with severe burns or with liver or kidney disease.
Clotting factors
Clotting (coagulation) factors help to control bleeding and work together with blood platelets to ensure that the blood clots effectively.
Fresh frozen plasma and clotting factor concentrates can be used to treat blood clotting disorders such as haemophilia, where an inherited lack of a specific clotting factor can cause prolonged bleeding.
Immunoglobulins
Immunoglobulins are part of the immune system (the body’s natural defence against illness and infection).
Immunoglobulins are antibodies that the body produces to fight unwanted viruses and bacteria. For example, they are used to fight health conditions such as:
- tetanus – a serious but usually short-lived bacterial infection
- hepatitis – a viral infection that causes the liver to become inflamed (swollen)
- rabies – an infection of the central nervous system that is passed on to humans from infected animals
Normal human immunoglobulins can be used to support people who are having cancer treatment when their immune system is having difficulty producing antibodies.
Plasma is the source of anti-D immunoglobulin, a substance that is often given by injection to pregnant women with a rhesus negative blood group (RhD negative) and whose unborn baby may have a rhesus positive blood group (RhD positive).
This treatment prevents the mother becoming sensitised to the baby’s blood and stops immune anti-D developing. Immune anti-D can cause Rhesus disease in subsequent pregnancies, which is a potentially fatal condition.
