Human blood is made up of four components: red blood cells (RBC), white blood cells (WBC), platelets and plasma. Plasma constitutes almost 55% of our blood, RBCs make up for 45% and the rest is made up of WBCs and platelets. Plasma is mostly water (92%) and proteins (and other organic molecules) (8%) and acts as the fluid medium of blood. An adult human being may contain up to 3 liters of plasma. Its main purpose is to circulate nutrients and remove waste products from the body. RBCs, or erythrocytes, contain hemoglobin and transport oxygen to all the tissues of it and remove the carbon dioxide. WBCs, or leukocytes, protect us from infection and pathogens and are part of the immune system. Platelets are responsible for blood clotting at the wound site.