Function, Formation and Regulation of Red Blood Cell

Function, Formation and Regulation of Red Blood Cell

Red Blood Cell and Hemoglobin

The major function of red blood cells, also known as erythrocytes, is to transport hemoglobin, which in turn carries oxygen from the lungs to the tissues. After birth, red blood cells are produced exclusively in the bone marrow. Red blood cells live for approximately 120 days. As they reach this age they become fragile and are removed from circulation by cells of the tissue macrophage system (liver, spleen and bone marrow).

Any condition (hemorrhage, high attitude, cardiac failure, lung disease) causes the quantity of oxygen transported to the tissues to decrease ordinarily increases the rate of red blood cell production. Thus, when a person becomes extremely anemic as a result of hemorrhage or any other condition, the bone marrow immediately begins to produce large quantities of red blood cells. Also, destruction of major portions of the bone marrow by any means, especially by x-ray therapy, causes hyperplasia (abnormal increase in the number of normal cells in normal arrangement in an organ or tissue, which increases its volume) of the remaining bone marrow, thereby attempting to supply the demand for red blood cells in the body.

When both kidneys are removed from a person or when the kidneys are destroyed by renal disease, the person invariably becomes very anemic because the 10 per cent of the normal erythropoietin formed in other tissues (mainly in the liver) is sufficient to cause only one third to one half the red blood cell formation needed by the body.

Hemoglobin and Carriage of Oxygen

Hemoglobin is the constituent of the red blood cell that combines with oxygen and consists of two parts, hem and globin. Hem contains iron in the ferrous (Fe2+) state. Iron is an essential part of hemoglobin and when deficiency occurs due to dietary inadequacy or loss through chronic hemorrhage, anemia results. The most important feature of the hemoglobin molecule is its ability to combine loosely and reversibly with oxygen.

The amount of oxygen the blood carries is described as the oxygen content of blood. Although the vast majority of oxygen is carried bound to hemoglobin, a very small amount is dissolved in the plasma.

Under normal circumstances, as blood leaves the lungs, hemoglobin is almost fully saturated with oxygen and each gram of hemoglobin contains 1.39ml of oxygen. However, by the time it reaches the systemic circulation this has fallen slightly due to the addition of a small volume of venous blood from the pulmonary and coronary circulations. Therefore in the arterial circulation, one gram of hemoglobin is around 98% saturated and contains 1.34ml of oxygen. Therefore 1gm of hemoglobin can combine with 1.34 ml of oxygen in arterial blood. A maximum of 0.03 ml of oxygen can dissolves in 100ml of blood at one atmosphere.