Sunday, May 11, 2008

Blood and the Type

Blood is the essential red fluid that is pumped by the heart trough the circulatory system of humans and all higher animals. It is complex in its composition and its functions. Blood has two main constituents. The cells, or corpuscles, comprise about 45 percent, and the liquid portion, or plasma, in which the cells are suspended comprises 55 percent. The blood cells comprise three main types, each with specific functions; red blood cells, white blood cells and platelets.

Red Blood Cells
Red blood cells, or erythrocytes, are tiny, round, biconcave disks averaging7.5 microns (0.003 in) in diameter. A normal 76.5 kg (170-lb) main has about 5 l (5.3 qt) of blood, containing more than 25 trillion red cells. Because the normal life span of red cells is only about 120 days, more than 200 billion cells are normally destroyed each day by the spleen and must be replaced. Red cells are made in the bone marrow.

The main function of the red blood cells is to transport oxygen from the lungs to the tissue. Oxidations of various food substances to supply most of the energy requirements of the body results in carbon dioxide, one of the chief waste products, and red blood cells carry it to the lungs for release and to pick up more oxygen.

The substance in the red blood cells that is largely responsible for their ability to carry oxygen and carbon dioxide is hemoglobin, the material that gives the cells their red color. Produced in the bone marrow and broken down in the spleen, it is a protein complex comprising many linked amino acids, and occupies almost the entire volume of a red blood cell. Essential to its structure and function is iron.

Blood Typing
The cell wall contains many antigenic proteins, which determine the blood type. Among these proteins are the antigens. A and B, the major blood group factors. Blood with antigen B is group B. Blood with both antigens is called AB, and blood with neither is called group O. Normally, the plasma of every person contains an antibody against the A or B antigens in the red cells are determined by mixing the cells with known typing serums. The antibodies in the serum or plasma are determined by mixing it with cells of known A or B type. Such typing is necessary in preparation for blood transfusion. Antigens of the various Rh and Hr types, M and N, S and Kell, Duffy, and many others also exist in the red blood cell. All like the A and B antigens, are inherited. When the red cell antigens are determined, they show so many different combinations as to make a persons blood type almost as individual as a fingerprint.

Antibodies against antigens other than A and B do not normally occurs in the plasma. They may appear after transfusion, however, and may cause transfusion reactions and destruction of red blood cells or hemolytic disease of the newborn.
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