RBC-Introduction, Morphology, properties, Lifespan, Fate of RBC & function.
Red blood cells (RBCs) Introduction .
[1]. Red blood cells (RBCs) are the non-nucleated formed elements in the blood. Red blood cells are also known as erythrocytes (erythros = red).
[2]. Red color of the red blood cell is due to the presence of the coloring pigment called hemoglobin
[3]. RBCs play a vital role in transport of respiratory gases.
[4]. RBCs are larger in number compared to the other two blood cells, namely white blood cells and platelets.
Normal Value of RBC .
RBC count ranges between 4 and 5.5 million/cu mm of blood.
In adult males, it is 5 million/cu mm .
In adult females, it is 4.5 million/cu mm.
Morphology of Red Blood Cells.
 |
| Dimensions of RBC. A. Surface view, B. Sectioned view. |
1. Normal Shape of RBC .
[1]. Normally, the RBCs are disk shaped and biconcave (dumbbell shaped). Central portion is thinner and periphery is thicker.
[2]. The biconcave contour of RBCs has some mechanical and functional advantages.
Advantages of Biconcave Shape of RBCs .
1. Biconcave shape helps in equal and rapid diffusion of oxygen and other substances into the interior of the cell.
2. Large surface area is provided for absorption or removal of different substances.
3. Minimal tension is offered on the membrane when the volume of cell alters.
4. Because of biconcave shape, while passing through minute capillaries, RBCs squeeze through the capillaries very easily without getting damaged.
2. Normal Size of RBC .
[1]. Diameter : 7.2 µ (6.9 to 7.4 µ).
[2]. Thickness : At the periphery it is thicker with 2.2 µ and at the center it is thinner with 1 µ . This difference in thickness is because of the biconcave shape.
[3]. Surface area : 120 sq µ.
[4]. Volume : 85 to 90 cu µ.
3. Normal Structure of RBC .
[1]. Red blood cells are nonnucleated. Only mammal, which has nucleated RBC is camel. Because of the absence of nucleus in human RBC, the DNA is also absent.
[2]. Other organelles such as mitochondria and Golgi apparatus also are absent in RBC. Because of absence of mitochondria, the energy is produced from glycolytic process.
[3]. Red cell does not have insulin receptor and so the glucose uptake by this cell is not controlled by insulin. RBC has a special type of cytoskeleton, which is made up of actin and spectrin.
[4].Both the proteins are anchored to transmembrane proteins by means of another protein called ankyrin. Absence of spectrin results in hereditary spherocytosis. In this condition, the cell is deformed, losses its biconcave shape and becomes globular (spherocytic).
[5]. The Spherocyte is very fragile and easily ruptured (hemolyzed) in hypotonic solutions.
Properties of RBC .
1. Rouleaux Formation .
When blood is taken out of the blood vessel, the RBCs pile up one above another like the pile of coins. This property of the RBCs is called rouleaux (pleural = Rouleau) formation . It is accelerated by plasma proteins globulin and fibrinogen.
2. Specific Gravity of RBC .
Specific gravity of RBC is 1.092 to 1.101.
3. Packed Cell Volume [PCV] .
Packed cell volume (PCV) is the proportion of blood occupied by RBCs expressed in percentage. It is also called hematocrit value. It is 45% of the blood and the plasma volume is 55% .
4. Suspension Stability of RBC .
During circulation, the RBCs remain suspended uniformly in the blood. This property of the RBCs is called the suspension stability.
Lifespan of RBC .
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 .
[1]. Lifespan of the RBC is determined by radioisotope method. RBCs are tagged with radioactive substances like radioactive iron or radioactive chromium.
[2]. Life of RBC is determined by studying the rate of loss of radioactive cells from circulation.
Fate of RBC .
 |
| Fate of RBC |
[1]. 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.
[2]. 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.
[3]. 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.
[4]. Hemoglobin is immediately phagocytized by macrophages of the body, particularly the macrophages present in liver (Kupffer cells), spleen and bone marrow.
[5]. Hemoglobin is degraded into iron, globin and porphyrin.
[6]. 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 .
[6]. Porphyrin is degraded into bilirubin, which is excreted by liver through bile .
[7]. Daily 10% RBCs, which are senile, are destroyed in normal young healthy adults.
[8]. 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.
Function of RBC .
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 .
[1]. Hemoglobin combines with carbon dioxide and form carbhemoglobin. About 30% of carbon dioxide is transported in this form.
[2]. RBCs contain a large amount of the carbonic anhydrase. This enzyme is necessary for the formation of bicarbonate from water and carbon dioxide .
[3]. Thus, it helps to transport carbon dioxide in the form of bicarbonate from tissues to lungs.
[4]. 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 acid-base 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 .
Thanks for Visiting us .
