When an anticoagulated sample of blood is allowed to stand in a narrow tube, on settling it separates into two major components –

  • The cellular part – Blood cells or corpuscles.
  • The fluid part – Blood plasma.

The cellular component also called as formed elements of blood comprise 45% of total blood volume and consists of –

  • Erythrocytes or Red blood cells or Red Blood Corpuscles (RBC’s)
  • Leukocytes or White blood cells or White blood corpuscles (WBC’s)
  • Thrombocytes or Platelets

The blood cells float in the fluid component of blood called as plasma. Plasma has a soluble protein called Fibrinogen which is converted to fibrin during the clotting mechanism – forms a blood clot and the fluid that separates out is called Serum.


  • Normal Count:

In Males – 4.8-5.5 million/mm3

In Females – 4.5-5 million/mm3

  • Shape: RBC’s are biconcave discs, this shape helps in rendering the red cells quite flexible so that they can easily pass through capillaries.
  • Size: 7.2 µm.
  • Nucleus – Erythrocytes are non-nucleated cells
  • Pigment present: Iron-containing pigment – Hemoglobin is present – helps in the transport of oxygen from the lungs to tissues and carbon dioxide from tissues back to the lungs.
  • Lifespan – 120 days.

Check out the functions of Erythrocytes or Red Blood Cells….


Leukocytes are the Nucleated blood cells that are associated with the defense process of the body in response to the invasion of the pathogenic microbe.

They are broadly divided into two categories: Granulocytes and Agranulocytes

Granulocytes: These are the leukocytes having granules in the cytoplasm. These include –

  1.) Neutrophils –

  • Normal Range: 50 – 70%
  • Shape: Spherical
  • Size: 10 – 14 µm
  • Nucleus: multilobed- 1-5 lobes, connected together with by chromatin. Stains purple with Leishman stain.
  • Cytoplasm: It appears bluish-pink when stained with Leishman stain, has fine pinpoint granules which can take both acidic and basic stains.
  • Pigment present: no pigment present – appears as colorless bodies.
  • Lifespan: 2-4 days

  2.) Eosinophils

  • Normal Range: 1-4%
  • Shape: Spherical
  • Size: 10-14 µm
  • Nucleus: usually Bilobed but Trilobed in some cases, stains purple with Leishman stain.
  • Cytoplasm: it is acidophilic – appears light pink color. Granules are coarse but do not cover the nucleus.
  • Pigment present: pigment is absent – appears as colorless bodies
  • Lifespan: 10-13 days

  3.) Basophils

  • Normal Range: 0-1%
  • Shape: Spherical
  • Size: 10-12 µm
  • Nucleus: usually bilobed, appears purple when stained with Leishman stain.
  • Cytoplasm: it is basophilic – purple-blue in color – granules are coarse, plenty in no. & overcrowding the nucleus resulting in the obscure boundary of nucleus & stain purple/blue in color with Leishman stain.
  • Pigment present: no – appears as colorless cells.
  • Lifespan: about 15 days

Agranulocytes: These are the leukocytes which lack cytoplasmic granules. These include –

  1.) Monocytes

  • Normal Range: 2-8%
  • Shape: Spherical cells
  • Size: 12-18 µm
  • Nucleus: pale colored, kidney-shaped, present in one side of the cell – when stained with Leishman stain.
  • Cytoplasm: It appears steel blue in color – when stained with Leishman stain.
  • Pigment present: No – appear as the colorless cell when unstained.
  • Lifespan: 3-5 days
  • Functions:

  2.) Lymphocytes

  • Normal Range: 20-30%
  • Shape: spherical
  • Size:

Small lymphocytes – 8-10 µm

Large lymphocytes – 15-20 µm

  • Nucleus: appears as Single, large, round/oval/indented, central occupies the whole cell leaving marginal space for cytoplasm when stained with Leishman stain.
  • Cytoplasm: scanty, pale-blue in color when stained with Leishman stain.
  • Pigment present: No appears as transparent cells
  • Lifespan: 3weeks to 1 year

Check out the functions of Leukocytes or White Blood Cells….


  • Normal Range: 1,50,000 – 4,50,000 /mm3
  • Shape: oval, round or rod-like
  • Size: 2-4 µm
  • Nucleus: non-nucleated cells
  • Cytoplasm: contains very small granules – stained reddish – purple
  • Pigment present: no
  • Lifespan: 3-10 days

Check out the functions of Thrombocytes or Platelets….


Plasma is a clear, straw-colored fluid part of the blood and represents 55% of the total blood volume.

It is composed of 91-92% water, 7-8% proteins and 1-2% other solutes.

Plasma proteins include –

  • Albumin – 55%
  • Globulin – 37%
  • Fibrinogen – 7%
  • Other proteins – 1%

The other solutes present in blood includes –

  • Non – protein nitrogenous substances – Urea, Uric acid, Creatinine, Creatine, Aminoacids, Xanthine and Ammonium Salts.
  • Non – nitrogenous substances – fats, cholesterol, phospholipids, lecithin, glucose, galactose, lactose.
  • Inorganic salts – Chloride, Phosphates, sodium, potassium, calcium, magnesium
  • Pigments e.g. bilirubin, carotene, xanthophyll
  • Enzymes, antibodies, hormones, immune bodies, compliments etc.


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