Three components of your blood are used by hospitals to treat patients in need of blood transfusions.
One of the blood cells that carry oxygen. Red cells contain hemoglobin and it is the hemoglobin that permits them to transport oxygen (and carbon dioxide). Hemoglobin, aside from being a transport molecule, is a pigment. It gives the cell its red color (and name). A red blood cell is sometimes simply referred to as a red cell. It is also called an erythrocyte.
An irregular, disc-shaped element in the blood that assists in blood clotting. During normal blood clotting, the platelets clump together (aggregate). Although platelets are often classed as blood cells, they are actually fragments of large bone marrow cells called megakaryocytes.
The liquid part of the blood and lymphatic fluid, which makes up about half of its volume. Plasma is devoid of cells and, unlike serum, has not clotted. Blood plasma contains antibodies and other proteins.