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Structure and Function of Red Blood Cells and White Blood Cells

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Structure and Function of Red Blood Cells and White Blood Cells Bloods importance to human life has been recognised since pre-history, acquiring mystic and religious significance through the ages. Biologically, blood is a liquid tissue, transporting materials and protecting us against disease. Suspended in the watery plasma are red and white blood cells, serving different functions, but both of vital importance to our bodies. Red Blood Cells (RBC's or erythrocytes) RBC's are responsible for carrying oxygen (O2) and removing carbon dioxide (CO2) from about 30 trillion cells in the human body. In normal blood RBC's account for about 45% of the total volume. On average, we have about 5 million red cells per cubic millimetre of blood. Produced in the red marrow of bones, RBC's arise from a single type of cell, called a stem cell. During formation the nucleus is lost and organelles degraded, allowing more internal space to be filled with haemoglobin, the O2 carrying protein abundant in red cells. ...read more.


Haemoglobin also carries CO2 from the cells, which is returned to the lungs. 95% of CO2 generated is carried by RBC's (containing the enzyme carbonic anhydrase to speed up the process). About 5% of CO2 is dissolved in blood plasma. (A good thing too: if all CO2 were carried this way blood pH would drop to an instantly fatal 4.5!). It is essential that blood pH is maintained, and haemoglobin acts as a powerful buffer in maintaining a pH of about 7.4. White Blood Cells (WBC's or leucocytes) Making up less than 1% of the total blood volume, WBC's like red cells are mostly formed from stem cells in the bone marrow. They have a defensive role in destroying invading organisms, and also assist the removal of dead or damaged tissue cells. White cells consist of lymphocytes and monocytes, with relatively clear cytoplasm, and 3 types of granulocyte - neutrophils, eosinophils and basophils, whose cytoplasm is filled with granules. Unlike RBC's, WBC's contain nuclei, they are also much larger and colourless. ...read more.


Monocytes leave the blood and become tissue macrophages, which remove dead and damaged cell debris, as well as antigens, which enter the body; these include organisms, which cause TB. Lymphocytes (app. 20-50% of WBC's) have a spherical nucleus and shape, with little cytoplasm. They have a diameter of 6-18 �m, and vary greatly in life span. They are the most numerous WBC in young children. The two major types of lymphocyte found in the blood are "B cells" and "T cells". Both B and T cells are commonly found in the lymph nodes and spleen. B cells are responsible for making antibodies. T cells recruit other WBC's to sites of infection/tissue damage. They also kill 'virus infected' cells and enhance the production of antibodies by B cells. The human immunodeficiency virus (HIV) binds to CD4 molecules on T cells, invading and infecting these cells. Other T cells destroy these infected cells, reducing their numbers. This makes the person susceptible to bacterial and viral infections, as well as certain cancers. Without modern drug treatment to support the body's immune system, many patients die of advanced stage HIV (or AIDS), due to the body's inability to fight infection. ...read more.

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