MORPHOLOGY OF RED BLOOD CELLS

Red blood cells (RBCs) are the non-nucleated formed elements in the blood. Red blood cells are also known as erythrocytes (erythros = red). Red color of the red blood cell is due to the presence of the coloring pigment called hemoglobin. RBCs play a vital role in transport of respiratory gases. RBCs are larger in number compared to the other two blood cells, namely white blood cells and platelets.

NORMAL VALUE

RBC count ranges between 4 and 5.5 million/cu mm of blood. In adult males, it is 5 million/cu mm and in adult females, it is 4.5 million/cu mm.

MORPHOLOGY OF RED BLOOD CELLS

NORMAL SHAPE

Normally, the RBCs are disk shaped and biconcave (dumbbell shaped). Central portion is thinner and periphery is thicker. 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.

NORMAL SIZE

Diameter : 7.2 μ (6.9 to 7.4 μ).

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.

Surface area : 120 sq μ.

Volume : 85 to 90 cu μ.

NORMAL STRUCTURE

Red blood cells are nonnucleated. Only mammal,

which has nucleated RBC is camel. Because of the absent. 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. 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. 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). The spherocyte is very fragile and easily ruptured (hemolyzed) in hypotonic solutions.

PROPERTIES OF RED BLOOD CELLS

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.

SPECIFIC GRAVITY

Specific gravity of RBC is 1.092 to 1.101.

PACKED CELL VOLUME

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% (Chapters 7 and 13).

SUSPENSION STABILITY

During circulation, the RBCs remain suspended uniformly in the blood. This property of the RBCs is called the suspension stability

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