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Fractions of Blood

In this series of articles, medical students from across the country will share their knowledge of medical physiology, anatomy and biochemistry to give you a taster of medical school. This will be a fantastic opportunity to build upon your A-Level Knowledge.

Remember it's more important to understand the principles than to mindlessly memorise facts.


Blood fractions are split into major and minor fractions. The 4 primary or major blood components include red blood cells, white blood cells, platelets and plasma. Fractionation of blood is typically done by centrifuging the blood in order for it to separate into different parts. The process of centrifugation describes when a solution is spun at high speed thus allowing separation between heavier parts of the solution. Once these heavier components have separated, they can be removed and, if necessary, the process can be repeated to further isolate parts of the solution. Plasma for example separates into a clear solution in the upper phase while erythrocytes (red blood) end up at the bottom of the centrifuge tube. Plasma can be further separated into its own fractions, in a process aptly named ‘blood plasma fractionation. These fractions are what are referred to as the minor fractions of blood, as they are components of the major fractions. Plasma is mostly comprised of water, roughly ninety percent of it is water – this is what gives it the straw colour. Another 8% is made up of proteins and clotting factors (which are very helpful in medical practice) and the remaining percentages by salts, glucose and lipids circulating in the blood. The minor classes of plasma blood fractions are immunoglobulins, clotting factors and albumin.

Immunoglobulins, also known as antibodies, are a protein base for many vaccines, for example tetanus, the MMR (measles, mumps and rubella) vaccine and even anti-snake venom. They are crucial for modern medical practice, being used to treat conditions spanning from infections to cancer.

Albumin as stated earlier is also isolated from plasma, as it is manufactured in the liver and then distributed throughout the body through the blood. It is made in the liver from plasma. Albumin is very helpful in medical practice as it can increase plasma volume, making it perfect to replace blood volume loss from trauma, burns, injuries as well as after surgery if there has been a considerable blood volume loss. In addition to this, albumin has an ability to bind and transport other substances throughout the circulatory system, a property which has been exploited to manufacture other medications or make them perform in a particular way.

Clotting factors can also be extracted from plasma through blood plasma fractionation, and examples such as the minor fractions cryoprecipitate and fibrinogen can be prescribed to patients if they have bleeding or clotting problems, causing them excessive blood loss. Cryoprecipitate actually has several clotting factors, including fibrinogen as well as factor 8 (the protein which is absent in those with haemophilia A), factor 13 and von Willebrand Factor. Some of these clotting factors are also available in synthetic forms, meaning they have not been gained through fractionation of donated blood, which can pose less of an ethical dilemma for those following certain religions. These minor fractions of blood may be administered to patients with a platelet dysfunction, if the patient has low levels of certain clotting factors or if a patient needs many blood components at one time.

Of course, donated blood goes through a large screening process, from the moment is donated, where donors are screened for many bloodborne infectious diseases as well as before and after being fractionated when it is sent for additional tests for disease. The fractionation process in itself decreases bacterial and viral contamination through alteration to pH as well as changed temperature and an ethanol concentration. Despite this, risk for disease transmission cannot be said to be eliminated.

Further Reading;


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