Blood Functions and Compositions


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	Blood Functions and Compositions

Leukemia Society of America, 1994

Blood Functions and Composition
The blood is a vital organ which supplies oxygen, food and other essential nutrients, hormones and chemicals to cells throughout the body. It serves as one of the body’s most effective defenses against infection, and it also helps in the removal of toxins and other waste materials.

Whole blood is made up of many components, with each component performing a specific role in the blood’s overall functions. The three main blood elements involved in leukemia are the red cells, clotting cells and white cells which are formed in the bone marrow and lymph nodes and circulate through the bloodstream in a clear fluid plasma.

Red Blood Cells (Erythocytes) contain hemoglobin, an iron rich protein which picks up oxygen as the blood passes through the lungs, transports it, and releases it to organs and tissues throughout the body. A shortage of these red cells, a condition known as anemia, can cause weakness, dizziness, shortness of breath, headaches and irritability.

Clotting Cells (Platelets) are tiny disc-shaped cells which help prevent abnormal or excessive bleeding by forming clots. A deficiency of platelets can cause bleeding of the mucous membranes or other tissues, such as the skin. Unexplained or excessive bruising is characteristic of a platelet deficiency.

White Blood Cells (Leukocytes) play a major role in defending the body against disease producing bacteria, viruses and fungi. There are three main types of leukocytes, with each type performing a specific infection-fighting function.

Monocytes defend the body against bacterial infection.

Granulocytes include neutrophils, eosinophils and basophils. Neutrophils are the predominant type, counting for about 60 percent of all circulating white blood cells. They combat infection by rapidly increasing in number, engulfing and destroying foreign substances. They then die and, in turn, are ingested by monocytes. Once an infection is under control, production of neutrophils returns to the original preinfection count and steady state. Eosinophils and basophils also play infection fighting roles.

Lymphocytes consist of two types of cells which combine forces to create a complex interaction to regulate the immune response. T cells attack virus-infected and malignant cells. B cells produce and release antibodies, or protein substances, which bind to infectious agents and help prevent them from doing damage to the body. A deficiency in any type of normal white blood cell may result in an increased susceptibility to infections.

Blood Cell Growth
The blood, like all human tissues and organs, is composed primarily of cells which are developed enough to perform efficiently. The red, white and clotting cells enter the bloodstream after the maturation process called hematopoiesis, which begins with the production of immature cells in the blood-forming tissue of the bone marrow, spleen or lymph nodes. Actually, only a small percentage of cells are produced in the spleen and lymph nodes. The majority of cells originate and mature in the bone marrow - the spongy meshwork interior which fills the cavities of the large bones.

Blood cells grow in the same general manner as all other human cells. Tissues or organs of the body contain a pool of immature, or undifferentiated cells known as stem cells. These cells begin to divide and mature until they become fully developed, or differentiated cells.

The original cells involved in blood cell production are called pluripotent stem cells, meaning that they contain the characteristics of all the different cell types which make up the major blood cell lines. One of these lines is known as the myeloid line which produces the white cells called monocytes and granulocytes. Another is the lymphoid line which produces lymphocytes. As cells mature, they are released into the blood stream to replace those which have become old and worn out.

Blood cells are not released from the bone marrow until they are "mature enough" to perform efficiently. Normally, immature cells or "blasts" are not present in the bloodstream. A relatively small amount of these cells are contained in the bone marrow, still involved in the growth process. However, blasts normally never constitute more that 5 percent of the bone marrow cells.

The entire blood cell reproduction, maintenance, and destruction cycle is really a highly efficient and orderly process. The abnormal and excessive reproduction of any type of cell obviously disrupts the delicate blood cell balance necessary to sustain the body’s general well-being.