The old saying, blood is the river of life, is genuinely true. Blood is the most important constituent of human body and it forms the circulatory system. It occupies 8% of total body weight and has an average density of about 1060 kg/m3. The intricate network of veins and arteries, distributes blood throughout the body. The pumping action of the heart helps in circulation of blood.
Red Blood Cells RBCs are also known as red blood corpuscles or erythrocytes. They constitute 45% of blood by volume. They contain hemoglobin, that renders blood red in color. RBCs are produced in the bone marrow and they have a life cycle of days. Mature RBCs are biconcave and flexible, lacking cell nucleus and organelles. The principle function is to deliver oxygen to different tissues of the body.
White Blood Cells WBCs or white blood corpuscles are known as leukocytes. They make for 1% by volume of total blood. Leukocytes are cells of the immune system that provide protection to the body from foreign particles and infectious diseases. They are derived from hematopoietic stem cells. Leukocytes are classified as granulocytes and agranulocytes. Granulocytes cells include neutrophils, basophils and eosinophils, whereas agranulocytes cells are lymphocytes, monocytes and macrophages. The count of leukocytes in blood is an important factor for normal functioning of body.
Platelets Platelets are also known as thrombocytes. They are derived from precursor cells known as megakaryocytes and are devoid of nucleus. The lifespan of platelets is 5-9 days. The most important function of platelets is blood coagulation or blood clotting. If the count of platelets in blood is low, they cause excessive bleeding while the effect is just reverse if the count is more than normal. They are also a source of natural growth factors.
circulatory system the system responsible for circulating blood and lymph throughout the body, that supplies nutrients and oxygen to the cells and removes various waste products: it consists of the heart, blood, blood vessels, lymph, etc. Venous vessels bringing blood to the heart and arteries vessels efferent blood from the heart.
blood group There are four major blood groups determined by the presence or absence of two antigens – A and B – on the surface of red blood cells: Group A – has only the A antigen on red cells (and B antibody in the plasma) Group B – has only the B antigen on red cells (and A antibody in the plasma) Group AB – has both A and B antigens on red cells (but neither A nor B antibody in the plasma) Group O – has neither A nor B antigens on red cells (but both A and B antibody are in the plasma) There are very specific ways in which blood types must be matched for a safe transfusion. See the chart below: