Red Blood Cells vs Platelets
Blood is a fluid type connective tissue, composed of a fluid matrix known as plasma and different kinds of cells and other formed elements that circulate within the fluid. It flows through the blood vessels in advanced animals. The main functions of blood are transportation of compound (such as oxygen, carbon dioxide), removal of excretory substances, distribution of hormones, regulation of water balance, body temperature etc, coagulation and protection against diseases. In an adult human, blood forms 7% to 8% of the whole body weight and contains around 5 liters. However, this total volume varies considerably with an individual’s size, composition of body, and state of training. Red blood cells, white blood cells, and platelets are collectively called formed elements. The formed elements constitute 40% to 50% of total blood volume. Red blood cells constitute more than 99% of the formed-element volume, while the rest (less than 1% of total formed element volume) constitute both white blood cells and platelets. Both red blood cells and platelets are formed in the red bone marrow and destroyed by phagocytosis.
Red Blood Cells
Red blood cells, also known as erythrocytes, are the main formed component of blood, and they constitute 45% of the blood volume in an adult human. Unlike the other formed-elements, the red blood cells contain hemoglobin, a pigment that binds and transport oxygen. Among mammals, the largest erythrocytes are found in elephant and the smallest in musk deer. Fishes, amphibians, and birds have oval, biconvex, and nucleated red blood cells while, in mammals, the red blood cells are circular, biconcave, and do not contain nuclei. Biconcave shape is important as it gives flexibility and facilitates quick diffusion of gases.
Platelets
Platelets are considered as cell fragments that pinch off from larger cells called megakaryocytes, the precursor to white blood cells found in bone marrow. Platelets are colorless and have granular cytoplasm. These fragments play an important role in blood coagulation, which prevents excessive blood loss. When a blood vessel is damaged, platelets accumulate at the damaged site and form a plug by sticking to one another and to the surrounding tissue. Platelets are approximately 3µm in diameter; very much smaller than the other formed-elements like red and white blood cells.
What is the difference between Red Blood Cells and Platelets?
• Red blood cells are complete cells, whereas platelets are considered as cell fragments.
• Red blood cells constitute more than 99% of total formed-element volume, while platelets constitute less than 1% of it.
• Red blood cells contain hemoglobin, while platelets lack hemoglobin.
• Platelets are smaller than red blood cells.
• Red blood cells transport oxygen, while platelets are required for blood coagulation or clotting.
• Mammalian red blood cells are circular, biconcave whereas, platelets are spindle shaped elements.
• Platelets are colorless, whereas red blood cells appear yellowish when a single cell is seen.
• Human red blood cells survive for about 120 days whereas platelets survive for 3 to 7 days.
• Red blood cells are destroyed either in blood or in spleen and liver. In contrast, platelets are destroyed only in blood.