Circulatory System of Class 11

Erythrocytes (RBC): Size and shape varies in different group animals.

Fishes, amphibians, reptiles and aves have nucleated erythrocytes whereas mammals (except camel and Llama) have non-nucleated erythrocytes, circular or discoid, biconcave, devoid of all cellular organelles, elastic in nature.

Average diameter: 7—8 µm Number/lit: 3.9—6.5 × 1012.

Average number : 500,000/mm3 (in male). Average number : 450,000/mm3 (in female).

Life span: 90—120 days. Destruction site: Spleen.

Formation and destruction period: Throughout life.

Leukocytes (WBC): Irregular, nucleated, without haemoglobin.

Average number: 5,000-10,000/mm3. Ratio (WBC : RBC) = 1 : 600.

Life span: 24 hours.

Types of granulocytes

Neutrophils: 60-70%, most active type of WBC.

Life span: 15 hours multilobular nucleus, Drumstick nucleus.

Average size: 12—14 mm. Number/lit: 2.0—7.5 × 109.

Function: Kills bacteria and other foreign particles.

Eosinophils: 1-4% of WBC, bilobular nucleus (spectacle shaped).

Life span: Few days. Average size : 16 mm

Number/lit: 1.3—3.5 × 109.

Function: Immunity system.

Basophils : 0.2—1 % of total WBC, nucleus ‘S’ shaped/Trilobed.

Life span: 3—7 days, Constituents: Heparin, histamine, and serotonin.

Average size: 14—16 mm. Number/lit: 0—0.44 × 109.

Function : Act as circulating mast cells.

Agranulocytes (non-granular WBC)


Lymphocytes: 25—30% of total WBC, large and almost round nucleus.

Size: Average diameter = 6—15 mm. Life span : Variable.

Number/lit : 0—0.9 × 109.

Function: Destruction of bacteria and other pathogens (immunity system).

Monocytes: 2—8% of total WBC. Centrally placed, ovoid or intended nucleus; Horse shoe shape.

Average size: 12—20 µm. Life span: 2—3 days

Number/lit: 0.2 — 0.8 × 109

Functions : Defense mechanism.

Thrombocytes (blood platelets): Irregular, anucleated, originates from Megakaryoblast / Megakaryocytes of bone marrow

Average size: 2—3 mm. Life span: 8—12 days.

Number/lit: 150—400 × 109. Function: Blood clotting.

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