Plasma, << PLAZ muh, >> is the liquid portion of blood. This yellowish, transparent fluid makes up more than half the volume of blood in the human body. The solid parts of blood–the red and white blood cells and the platelets–are suspended in the plasma. Plasma consists of more than 90 percent water. A variety of dissolved substances, including proteins, salts, digested foods, and wastes, make up the rest of the plasma.
Functions of plasma.
Plasma makes the blood fluid. Without this characteristic, blood could not perform its job of transporting vital substances throughout the body. Plasma carries blood cells and platelets to all parts of the body. It also transports digested foods to the body tissues. It picks up soluble waste materials from the tissues and carries them to the kidneys for excretion from the body. Plasma also transports hormones that help control the function and development of many parts of the body.
The three major types of plasma proteins–albumin, globulins, and fibrinogen–each serve important functions. Albumin helps maintain a balance between the amount of fluid that leaves and enters the blood vessels. If plasma does not have enough albumin, excessive fluid passes through the blood vessels and accumulates in the tissues, causing the body to swell. In addition, albumin binds and carries nutrients absorbed from the digestive system.
The globulins–particularly the gamma globulins–help protect the body from disease. Gamma globulins are antibodies, disease-fighting proteins that attack bacteria, viruses, poisons, and other harmful substances (see Immune system ).
Fibrinogen is the most abundant of a group of plasma proteins called clotting factors. These proteins prevent excessive loss of blood from injured vessels. When a person starts bleeding, a chain reaction involving the clotting factors takes place. This reaction results in the formation of a blood clot.
Uses in medicine.
Physicians use plasma for transfusions to provide clotting factors and other proteins. Plasma transfusions are used chiefly in the treatment of bleeding disorders. Because it contains most of the clotting factors, a transfusion of plasma can halt bleeding in many such cases. Plasma transfusions are also used to treat severe blood loss when whole blood is unavailable. Such transfusions have saved the lives of millions of soldiers injured in battle.
Blood banks obtain proteins from plasma through a process called fractionation. Proteins obtained in this way include gamma globulins and individual clotting factors. Doctors sometimes use gamma globulins to protect against or modify such infectious diseases as measles and viral hepatitis. They use an individual clotting factor to control hemophilia, a bleeding disorder caused by inherited deficiency or abnormality of a certain clotting factor.
Blood banks separate plasma from whole blood by allowing the solid components to settle by gravity or by using a machine called a centrifuge. A special donation technique called plasmapheresis removes only plasma, returning the blood cells and platelets to the donor. Blood banks freeze plasma intended for use in transfusions. Plasma intended for fractionation is sent to various companies for processing.
