Introduction and normal value

Erythrocytes or red blood cells (RBC) are the non-nuc­leated formed elements in the blood. The red colour of these cells is due to the presence of the colouring matter-hemoglobin in these cells. The word “erythros” means red.

Normal Values:

• in adult men – 4,5-5,5 x 10¹²/l;

• in adult women – 3,7-4,5 x 10¹²/l;

• in newborns – up to 7,0 x 10 ¹²/l;

• adult ciphras – up to adolescence.

MORPHOLOGY OF RED BLOOD CELLS

NORMAL SIZE

• diameter – 7,0-7,7 mcm – in normocytes; less than 6,0 mcm – microcytes, more than 7,7 mcm macrocytes;

• width – 2 mcm;

• volume – 76-100 mcm;

• surface square – 140-150 mcm²

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9. 2.2 p

FIGURE 2: Dimensions of red blood cell. A: Surface view. B. Sectioned view

Normally, the red blood cells are disc shaped and bicon­cave (dumb-bell shaped). The biconcave contour of red blood cells has the following mechanical advantages.

1. It 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. While passing through minute capillaries, these cells can squeeze through the capillaries very easily.

PROPERTIES OF RED BLOOD CELLS

1. ROULEAUX FORMATION

When blood is taken out of the blood vessel, the red blood cells pile up one above another like the pile of coins. This property of the red blood cells is called rouleaux (pleural = rouleau) formation (Fig.3).

2. SPECIFIC GRAVITY

The specific gravity of red blood cell is 1.092 to 1.101.

3. PACKED CELL VOLUME

When the blood is collected in a centrifuge tube along with proper anticoagulant and centrifuged for a period of 30 minutes at a speed of 3000 rpm (revolutions per minute), the red blood cells settle at the bottom of the tube leaving the clear plasma at the top. The red blood cells form 45% of the total blood. This is called the packed cell volume or hematocrit. The volume of plasma is 55%.

4. SUSPENSION STABILITY

During circulation, the red blood cells remain suspended uniformly in the blood. This property of the red blood cells is called the suspension stability or sedimentation absence.

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FIGURE 3: Rouleau formation Courtesy: Dr Nivaldo Medieiros

This figure demonstrates “coin columns” formation or erythrocytes sedimentation that has been described in lesson number 31.

Variations in number of red blood cells

PHYSIOLOGICAL VARIATIONS

A. Increase in the red blood cell count is known as poly­cythemia. If it occurs in physiological conditions, it is called physiological polycythemia. Although some authors determine polycytemy as erythrocytes, leucocytes and platelets amount increase and the term “erythrocytosis” is used for erythrocytes increase designation. It occurs in the following conditions:

1. Age

At birth, the red blood cell count is 8 -10 millions/cu mm of blood. The count decreases within 10 days after birth due to destruction of cells causing physiological jaundice in some infants. However, in infants and growing children, the cell count is at a level higher than the value in adults.

2. Sex

Before puberty and after menopause in females the red blood cell count is similar to that in males. During repro­ductive period of females, the count is less than in males (4.5 millions/cu mm).

3. High Altitude

The inhabitants of mountains (above 10,000 feet from mean sea level) have an increased red blood cell count of more than 7 millions/cu mm. This is due to hypoxia in high altitude. During hypoxia, the erythropoietin is released from the kidneys. The erythropoietin in turn stimulates the bone marrow to produce more red blood cells.

4. Muscular Exercise

There is a temporary increase in red blood cell count after exercise. This is because of mild hypoxia and contraction of spleen, which is the reservoir of blood.

5. Emotional Conditions

The red blood cell count is increased during the emotional conditions like anxiety, because of sympathetic stimula­tion.

6. Increased Environmental Temperature

The increase in the atmospheric temperature increases red blood cell count.

7. After Meals

There is a slight increase in the red blood cell count after taking meals.

B. Decrease in red blood cell count (erythropeny) occurs in the follow­ing physiological conditions:

1. High Barometric Pressures

At high barometric pressures as in deep sea, when the oxygen tension of blood is higher, the red blood cell count decreases.

2. After Sleep

The red blood cell count decreases slightly after sleep.

3. Pregnancy

In extracellular fluid volume, increases the plasma volume also resulting in hemodilution. So, there is a relative reduction in the red blood cell count.