Why is blood red?

The blood flowing through arteries, veins and capillaries of our body comprises of different materials and cells with various functions. A major part of the blood is comprised of plasma. It is pale yellow in color, and thicker than water. It is dense as it consists of substances like proteins, antibodies, fibrinogen, carbohydrates, fats, salts and others.

Red blood corpuscles, or cells, are responsible for the red color of blood. There are about 35 trillion of these red blood cells; which are tiny. They render the red color to the blood as innumerable cells constitute the blood. As the young red blood cell matures, it sheds its nucleus, and increases its production of hemoglobin. Hemoglobin is the red pigment that resides in red blood cells, and imparts the red color to the blood. It is composed of iron (heme) and protein (globin).

Hemoglobin carries oxygen from the lungs to the cells throughout the body, and carries carbondioxide from the body parts to the lungs. When the iron in hemoglobin is in an oxidized state it is red in color, but in a non-oxidized state, it is blue in color.

There is a physical phenomenon behind the appearance of oxidized hemoglobin, and its red color. According to this, the combination of globin, oxygen and iron will absorb higher wavelength light, like blue and green, and reflects red light. This reflected red light is sensed by our eyes.

The life span for red blood cells is 120 days. The bone-marrow replenishes the red blood cells after the cells die. The synthesized cells keep circulating throughout the body. Some people think that there is blue colored blood in veins, but this is not correct. The blue color is due to the skin under which the veins are lying. Veins have dark red colored blood.