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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