Hematology is a science that deals with blood (blood cells). The term “hematology” has its origins in Greek words haima (blood) and logos (science), and was called into use for the first time in 1743. Blood is the red fluid circulating through blood vessels and is an essential power system in our body. It consists of a pale yellow liquid, the plasma, and blood cells.
The cells are the erythrocytes (or red blood corpuscles), the leukocytes (cells with nuclei), and the thrombocytes (blood platelets). They make 45% of the blood volume. The plasma makes 55% of the blood volume.
Figure 1: Volume ratio of blood cells and blood plasma (hematocrit)
The plasma consists of fibrinogen (a portion that can be coagulated), and a clear yellowish serum - a part of extracellular fluid, consisting of different proteins, electrolytes, and other components.
Blood cells, which wear themselves out in excessive quantities, make a unique hematopoietic system, together with the tissues in which they are formed. The circulation cells are just a section of the whole system.
The basic organ of hematopoesiesis is the bone marrow. All blood cells derive from it. Along with the bone marrow, the thymus, lymph nodes, and the spleen are the parts of the hematopoietic tissue.
The cells remain in blood for some time. Their stay there depends upon their types. The value of their permanency refers to the fact that the quantity of formed cells is evenly balanced with the quantity of damaged cells.