RBC

Red Blood Cells (RBCs)

Overview Morphology Properties Lifespan Fate Functions RBC Variations Size Shape Structure

1 Overview of Red Blood Cells

Red blood cells (RBCs) or erythrocytes are the non-nucleated formed elements in the blood.

Red color of RBCs is due to the presence of hemoglobin.

Normal RBC Count

Overall RBC Count

4–5.5 million/cu mm of blood.

Adult Males

5 million/cu mm

Adult Females

4.5 million/cu mm

2 Morphology of RBC

Normal Shape

  • Normally, RBCs are:
  • Disk shaped
  • Biconcave (dumbbell shaped)
  • Central portion → thinner.
  • Periphery → thicker.

Biconcave contour of RBCs has mechanical and functional advantages.

Advantages of Biconcave Shape of RBCs

  1. Biconcave shape helps in equal and rapid diffusion of oxygen and other substances to the interior of the cell.
  2. Large surface area is provided for absorption or removal of different substances from the cell.
  3. Minimal tension is offered on the membrane of the cell when volume alters.
  4. Because of biconcave shape, while passing through minute capillaries, RBCs squeeze through the capillaries very easily without getting damaged.

Normal Size of RBC

Diameter

7.2 μm (6.9–7.4 μm)

Thickness — Periphery

2.2 μm

Thickness — Center

1 μm

Surface Area

120 sq μm

Volume

85–90 cu μm

Difference in thickness is because of the biconcave shape.

Normal Structure of RBC

  • Red blood cells are non-nucleated.
  • The source states that the camel is the only mammal having nucleated RBCs.

3 Properties of Red Blood Cells

1. Rouleaux Formation

Rouleaux formation (pleural = rouleau) → piling up of RBCs one above another like a pile of coins.

  • It occurs when blood is taken out of the blood vessel and allowed to stand without movement.
  • It is accelerated by plasma proteins:
    • Globulin
    • Fibrinogen

2. Specific Gravity

Specific gravity of RBC → 1.092–1.101.

3. Packed Cell Volume

  • Packed cell volume (PCV) or hematocrit value → proportion of blood occupied by RBCs, expressed in percentage.
PCV

45% of blood.

Plasma Volume

55%.

4. Suspension Stability

Suspension stability → ability of RBCs to remain suspended uniformly in the blood during circulation.

4 Lifespan of RBC

Average lifespan of RBC → about 120 days.

Determination of Lifespan of RBC

  • Lifespan of RBC is determined by the radioisotope method.
  • RBCs are tagged with radioactive substances such as:
    • Radioactive iron
    • Radioactive chromium
  • Life of RBC is determined by studying the rate of loss of radioactive cells from circulation.

5 Fate of RBC

Destruction of Senile RBCs

  • After their lifetime, senile (old) RBCs are destroyed by macrophages present in:
    • Spleen
    • Liver
  • Most RBCs are destroyed in the spleen.
  • When RBCs become older (120 days):
    • Cell membrane becomes more fragile.
    • Diameter of capillaries is less than or equal to that of RBC.
    • Younger RBCs can pass through capillaries easily.
    • Older cells, because of their fragile nature, are destroyed while trying to squeeze through capillaries.
  • Destruction occurs mainly in capillaries of red pulp of spleen because the diameter of splenic capillaries is very small.
Spleen

Therefore, spleen is called the graveyard of RBCs.

Breakdown of RBC

  • Destroyed RBCs are fragmented.
  • Hemoglobin is released from fragmented parts.
  • Hemoglobin is immediately phagocytized by macrophages of the body, particularly macrophages present in:
    • Liver (Kupffer cells)
    • Spleen
    • Bone marrow
  • Hemoglobin is degraded into:
    • Iron
    • Globin
    • Porphyrin

Fate of Iron

  • Iron combines with a protein called apoferritin → ferritin.
  • Ferritin is:
    • Stored in the body.
    • Reused later.

Fate of Globin

Globin enters the protein depot for later use.

Fate of Porphyrin

  • Porphyrin is degraded into bilirubin.
  • Bilirubin is excreted by the liver through bile.

Daily Destruction of RBC

  • In normal young healthy adults:
  • 10% RBCs, which are senile, are destroyed daily.
  • This causes release of about 0.6 g/dL of hemoglobin into plasma.
  • From this, 0.9–1.5 mg/dL bilirubin is formed.
Significance of Destruction of Senile RBCs

Destruction of senile RBCs helps in the recycling process of iron in the body.

6 Functions of Red Blood Cells

Major function of RBCs → transport of respiratory gases.

1. Transport of Oxygen

  • Hemoglobin in RBC combines with oxygen → oxyhemoglobin.
  • About 97% of oxygen is transported in the form of oxyhemoglobin from:
    • Lungs → tissues.

2. Transport of Carbon Dioxide

  • Hemoglobin combines with carbon dioxide → carbhemoglobin.
  • About 30% of carbon dioxide is transported in this form from:
    • Tissues → lungs.
  • RBCs contain a large amount of carbonic anhydrase.
  • This enzyme is necessary for 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.
  • It regulates hydrogen ion concentration.
  • It plays a role in maintenance of acid-base balance.

4. In Blood Group Determination

  • RBCs carry blood group antigens such as:
    • A antigen
    • B antigen
    • Rh factor
  • This helps in:
    • Determination of blood group of a person.
    • Prevention of reactions due to incompatible blood transfusion.

7 Variations in Number of RBC

A. Increase in RBC Count — Polycythemia

Increase in RBC count is known as polycythemia.
  • It occurs in:
    • Physiological conditions
    • Pathological conditions
  • When it occurs in physiological conditions → physiological polycythemia.
  • Increase in this condition is:
    • Marginal
    • Temporary

Physiological Variations

1. Age
  • At birth:
    • RBC count → 8–10 million/cu mm of blood.
  • Count decreases within 10 days after birth due to destruction of RBCs.
  • Due to excess destruction of RBCs and liberation of bilirubin:
    • Physiological jaundice develops in some newborn babies between 2–3 days after birth.
    • This type of jaundice lasts only for a few days.
  • In infants and growing children:
    • RBC count is more than that in adults.
2. Sex
  • Before puberty and after menopause:
    • RBC count in females is similar to that in males.
  • During reproductive period of females:
    • RBC count is less than in males.
    • Female RBC count → 4.5 million/cu mm.
3. High Altitude
  • In people living in mountains above 10,000 feet from mean sea level:
    • RBC count is more than 7 million/cu mm.
  • It is due to hypoxia (decreased oxygen supply to tissues) in high altitude.
  • Hypoxia stimulates kidney to secrete erythropoietin.
  • Erythropoietin stimulates bone marrow to produce more RBCs.
4. Muscular Exercise
  • RBC count increases after muscular exercise.
  • It is because of mild hypoxia which increases:
    • Sympathetic activity
    • Secretion of adrenaline from adrenal medulla.
  • Adrenaline contracts spleen.
  • RBCs are released into blood.
  • Hypoxia also causes secretion of erythropoietin which stimulates bone marrow to produce more RBCs.
5. Emotional Conditions
  • RBC count increases during emotional conditions such as anxiety.
  • It is because of:
    • Increased sympathetic activity
    • Contraction of spleen.
6. Increased Environmental Temperature
  • Generally, increased temperature increases all activities of the body, including production of RBCs.
7. After Meals
  • There is a slight increase in RBC count after taking meals.
  • It is because of the need for more oxygen for metabolic activities.

B. Decrease in RBC Count

Decrease in RBC count occurs in the following physiological conditions:

1. High Barometric Pressures
  • At high barometric pressures, as in deep sea, oxygen tension of blood is higher.
  • RBC count decreases.
2. During Sleep
  • Generally, all activities of the body are decreased during sleep, including production of RBCs.
3. Pregnancy
  • In pregnancy, RBC count decreases.
  • It is because of:
    • Increase in ECF volume.
    • Increase in ECF volume increases plasma volume.
    • This results in hemodilution.
    • Therefore, there is a relative reduction in RBC count.

8 Pathological Variations

A. Pathological Polycythemia

Pathological polycythemia → abnormal increase in RBC count.

RBC count increases above 7 million/cu mm of blood.

Polycythemia is of two types:

  1. Primary polycythemia
  2. Secondary polycythemia.

1. Primary Polycythemia — Polycythemia Vera

  • Primary polycythemia is otherwise known as polycythemia vera.
  • It is a disease characterized by persistent increase in RBC count above 14 million/cu mm of blood.
  • It is always associated with increased WBC count above 24,000/cu mm of blood.
  • Polycythemia vera occurs due to malignancy of red bone marrow.

2. Secondary Polycythemia

Secondary polycythemia is pathological polycythemia occurring because of diseases in some other system.

Diseases Causing Pathological Polycythemia

  1. Respiratory disorders like emphysema
  2. Congenital heart disease
  3. Ayerza’s disease
    • A condition associated with:
      • Hypertrophy of right ventricle
      • Obstruction of blood flow to lungs
  4. Chronic carbon monoxide poisoning
  5. Poisoning by chemicals such as:
    • Phosphorus
    • Arsenic
  6. Repeated mild hemorrhages

B. Anemia

Anemia is the abnormal decrease in RBC count.

9 Variations in Size of RBC

Under physiological conditions, size of RBCs in venous blood is slightly larger than those in arterial blood.

1. Microcytes

Microcytes are smaller red blood cells.

They are present in

  1. Iron deficiency anemia
  2. Prolonged forced breathing
  3. Increased osmotic pressure in blood

2. Macrocytes

Macrocytes are larger cells.

They are present in

  1. Megaloblastic anemia
  2. Muscular exercise
  3. Decreased osmotic pressure in blood

Anisocytes

Anisocytes are red blood cells without uniform size.

Anisocytosis occurs in pernicious anemia.

10 Variations in Shape of RBC

Shape of RBCs is altered in many conditions, including different types of anemia.

Alteration in Shape of RBCs

1. Crenation

Shrinkage as in hypertonic conditions.

2. Spherocytosis

Globular form as in hypotonic conditions.

3. Elliptocytosis

Elliptical shape as in certain types of anemia.

4. Sickle Cell

Crescentic shape as in sickle cell anemia.

5. Poikilocytosis
  • Unusual variations in shape due to deformed cell membrane.
  • Shape may be:
    • Flask
    • Hammer
    • Any other unusual shape.

11 Variations in Structure of RBC

1. Punctate Basophilism

Striated appearance of RBCs due to presence of dots of basophilic materials (porphyrin) is called punctate basophilism.

It occurs in conditions like lead poisoning.

2. Ring in RBCs or Goblet Ring

  • Ring or twisted strands of basophilic material appear in the periphery of RBCs.
  • This appears in RBCs during some types of anemia.

3. Howell-Jolly Bodies

In certain types of anemia, some nuclear fragments called Howell-Jolly bodies are present in the ectoplasm of RBCs.

Red Blood Cells (RBCs)