Blood supplies oxygen, transports nutrients, waste, and hormonal messengers to each of the sixty billion cells in the body, and defends the body against foreign material. There are close to 30 trillion blood cells in an adult human. Each cubic millimeter of blood contains from 4 2 to 5 2 million red blood cells and an average total of 7,500 white blood cells. Blood has four main components: red blood cells, white blood cells, platelets, and liquid plasma. Since both red and white blood cells are continually being destroyed, the body must continue to produce new ones. About 2 2 million red blood cells die every second, at the same time, about 2 2 million new ones are created. .
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Sickle cell anemia is an inherited blood disorder characterized by defective hemoglobin. It affects millions of people throughout the world and approximately 72,000 people in the US. It is present in 1 in every 500 African-American births. Sickle cell anemia is an inherited disorder in which an abnormality occurs in the structure of hemoglobin. The disorder arises from a mutated gene for beta-globin, one of two kinds of polypeptide chains in the hemoglobin molecule. Hemoglobin is a substance found within red blood cells that is necessary for carrying oxygen. The chemical structure is known as hemoglobin A. Humans depend on the intake of oxygen for aerobic respiration. Oxygen in air flows into the lungs, then diffuses into the blood. There it binds to hemoglobin, which transport it through arteries, arterioles, and then capillaries threading past all living cells in the body. A steep oxygen concentration gradient exists between blood and the fluid within the surrounding tissues, so most of the oxygen diffuses into the tissues and into cells. With this extensive cellular uptake, the concentration of oxygen in blood declines. The abnormally formed hemoglobin allele is called hemoglobin S, or sickle hemoglobin.