FUNCTIONS OF RED BLOOD CELLS

FUNCTIONS OF RED BLOOD CELLS

Major function of RBCs is the transport of respiratory gases. Following are the functions of RBCs:

1. Transport of Oxygen from the Lungs to the Tissues

Hemoglobin in RBC combines with oxygen to form oxyhemoglobin. About 97% of oxygen is transported in blood in the form of oxyhemoglobin.

2. Transport of Carbon Dioxide from the Tissues to the Lungs

Hemoglobin combines with carbon dioxide and form carbhemoglobin. About 30% of carbon dioxide is transported in this form. RBCs contain a large amount of the carbonic anhydrase. This enzyme is necessary for the formation of bicarbonate from water and carbon dioxide. Thus, it helps to transport carbon dioxide in the form of bicarbonate from tissues to lungs. About 63% of carbon dioxide is transported in this form.

3. Buffering Action in Blood

Hemoglobin functions as a good buffer. By this action, it regulates the hydrogen ion concentration and thereby plays a role in the maintenance of acidbase balance.

4. In Blood Group Determination

RBCs carry the blood group antigens like A antigen, B antigen and Rh factor. This helps in determination of blood group and enables to prevent reactions due to incompatible blood transfusion

LIFESPAN OF RED BLOOD CELLS

Average lifespan of RBC is about 120 days. After the lifetime the senile (old) RBCs are destroyed in

reticuloendothelial system.

Determination of Lifespan of Red Blood Cells

Lifespan of the RBC is determined by radioisotope method. RBCs are tagged with radioactive substances

like radioactive iron or radioactive chromium. Life of RBC is determined by studying the rate of loss of radioactive cells from circulation.

FATE OF RED BLOOD CELLS

When the cells become older (120 days), the cell membrane becomes more fragile. Diameter of the

capillaries is less or equal to that of RBC. Younger RBCs can pass through the capillaries easily. However, because of the fragile nature, the older cells are destroyed while trying to squeeze through the capillaries. The destruction occurs mainly in the capillaries of red pulp of spleen because the diameter of splenic capillaries is very small. So, the spleen is called ‘graveyard of RBCs’. Destroyed RBCs are fragmented and hemoglobin is released from the fragmented parts. Hemoglobin is immediately phagocytized by macrophages of the body, particularly the macrophages present in liver (Kupffer cells), spleen and bone marrow. Hemoglobin is degraded into iron, globin and porphyrin. Iron combines with the protein called apoferritin to form ferritin, which is stored in the body and reused later. Globin enters the protein depot for later use. Porphyrin is degraded into bilirubin, which is excreted by liver through bile.

Daily 10% RBCs, which are senile, are destroyed in normal young healthy adults. It causes release of about 0.6 g/dL of hemoglobin into the plasma. From this 0.9 to 1.5 mg/dL bilirubin is formed.

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