During normal circumstances, roughly 55% of the blood volume in our arteries, veins and capillaries is made up of blood plasma, while the rest is mainly red blood cells, white blood cells and thrombocytes (platelets). Red blood cells carry oxygen and carbon dioxide, white blood cells are a part of the immune system and platelets are responsible for certain aspects of blood clotting (coagulation) and wound healing.
What is blood plasma?
It is the intravascular part of the body´s extracellular fluid. Blood plasma is a liquid that holds a variety of substances in suspension, including many important proteins. Plasma is carrying things to and from the cells throughout the body and is the main medium for excretory product transportation. Plasma is necessary for the intravascular osmotic effect that keeps the electrolyte concentration balanced in the body. Among other things, plasma is also an important part of the immune system.
Examples of what is present in plasma:
- Water (up to 95% of the plasma volume is water)
- Dissolved proteins, such as serum albumins, globulins and fibrinogen proteins
- Glucose (a type of sugar)
- Clotting factors
- Electrolytes (Na+, Ca2+, Mg2+, HCO3−, Cl−, and more)
- Carbon dioxide and oxygen
Blood plasma has a density of approximately 1.025 g/ml.
What does blood plasma look like?
When isolated, normal blood plasma looks yellowish. (The reason why our blood is red and not yellowish is the red haemoglobin present in the red blood cells.)
Plasma is yellowish due to the presence of bilirubin, carotenoids, transferrin and some haemoglobin. It is typically fairly transparent, but can also be opaque. Opaque plasma can be caused by abnormally high levels of lipids.
If plasma is green, orange or brown instead of yellowish, the unusual colour is typically cause for medical concern, although green colouration can also be a side effect of certain medicines.
Separating plasma from the rest of the blood
Blood plasma can be separated from the rest of the blood by adding an anticoagulant to a tube of fresh blood and then spin it in a centrifuge. The blood cells will go to the bottom of the tube, while the plasma goes to the top.
It is also possible to extract blood plasma from blood using filtration or via agglutination. These methods are commonly utilized for rapid testing of specific biomarkers.
Albumins, globulins and fibrinogen proteins in blood plasma
The most common plasma proteins are albumins, globulins and fibrinogen proteins.
Albumins, which are produced in the liver, are the most common plasma proteins. They are necessary to maintain the blood´s osmotic pressure and prevent bodily fluids outside the capillaries from moving into the bloodstream. If the albumins were to be removed from the whole blood, the consistency of the remaining blood would become more similar to the consistency of water.
Globulins are the second-most common type of proteins in blood plasma. They are are type of globular proteins with a higher molecular weight than albumins. Some globulins are produced in the liver, while others are created elsewhere by the immune system. One of the most famous of the globulin groups is the one comprised of immunoglobulins (Ig), also known as antibodies (Ab).
Fibrinogen proteins, which are produced in the liver, are a part of the body´s blood clotting system. In case of injury, fibrogen proteins are converted to form a fibrin-based blood clot. Interestingly, fibrogen proteins also limits clotting by reducing the activity of thrombin.
What is blood serum?
Blood serum is blood plasma without clotting factors.
The existence of plasma goes back several centuries, and plasma was for instance described by the English physician William Harvey in his 1628 work de Mortu Cordis. The use of plasma as a substitute for whole blood for certain transfusion purposes is a much more modern development, and the idea was not proposed until 1918 when Gordon R. Ward wrote about it in the British Medical Journal.
Plasmapheresis is a technique where a blood donor´s red blood cells can be returned to them soon after the donation so that only the remaining plasma is actually donated. The technique, which is still in use today, was pioneered by the Spanish MD José Antonio Grifols Lucas who opened his Laboratorios Grifols in 1940 and the world´s first plasma donation centre five years later.