Blood can be divided into two parts basically, the plasma and the blood cells, each of which constitutes about half of the total blood volume. The two parts are defined as follows:
1. Plasma – Plasma constitutes about 55% of the total blood volume and comprises of 92% water roughly. The rest includes dissolved proteins, salts, sugar, lipids, vitamins, fat, minerals, enzymes, antibodies, hormones and coagulants. Plasma provides mobility to the blood cells that remain suspended in it and it is due to the mobility which the plasma provides blood with, that the cells are able to receive oxygen and other nutrients from blood constantly, while excreting carbon dioxide and other wastes into it at the same time. Without the blood cells, plasma itself is a mostly clear, yellowish liquid.
2. Blood Cells – Blood cells can be divided into three major types, white blood cells, red blood cells and platelets.
a) White Blood Cells – White blood cells or leukocytes are rare in number and constitute approximately 1% of the total blood volume. There is more than one type of white blood cell and all of them together make up our immune system. Unlike the red blood cells which are found in blood only, the leukocytes are also found in the spleen, liver and the lymph glands.
b) Red Blood Cells – Erythrocytes (RBC) constitute almost half of the blood volume and their main function is to use the hemoglobin in them to carry dissolved oxygen to the cells and also to carry carbon dioxide from the cells for elimination.
c) Platelets – Like the erythrocytes, platelets do not have nuclei either, and their main function is to stop blood from flowing out of the vessels by releasing coagulating agents near the rupture. Release of proteins that help the immune system to fight with germs is also found to be a function of these cellular fragments recently.