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PinkMonkey Online Study Guide-Biology
Leucocytes are mainly of the following two types :
A) Granulocytes: They are distinctly amoeboid,
containing granular cytoplasm and a lobed nucleus in each. According to
their staining properties, they are classified as follows:
(i) Eosinophils: These are the granulocytes
the granules of which are large and can be stained with acidic dyes.
The nucleus is bilobed. They are about 5% of the total leucocytes. The
percentage of these cells increases when parasites or bacteria invade
the body.
(ii) Basophils: The granules of these
cells get stained with basic dyes, and the nucleus is more or less twisted.
They form 1% of the total number of leucocytes. The cytoplasmic granules
contain heparin, suggesting their anticoagulating function.
(iii) Neutrophils: The granules of these
cells are stained with neutral dyes. The nucleus is twisted and
more than two lobed. They form about 70% of the total number of
leucocytes. They are phagocytic in function, forming the first
line of defense against germs (bacteria, viruses etc.).
B) Agranulocytes: They usually contain clear cytoplasm
and a nucleus which is not lobed. They are of two types, namely:
(i) Monocytes, which are large and show
a kidney-shaped nucleus. They are phagocytic in function. They are about
1 to 5% of the total number of leucocytes.
(ii) Lymphocytes, which are small with
a comparatively large spherical nucleus in each. They produce antibodies
and antitoxins highly specific in their reactions. They form about 25%
of total leucocytes.
(3) Blood platelets: Platelets
are minute and oval discs about 2mm
in diameter. They are formed by the fragmentation of large cells called
megakaryocytes of bone marrow. They are about two hundred and fifty thousand
to three hundred thousand per cubic millimeter. When they come in contact
with a damaged vascular surface, they release a substance called thrombokinase
which initiates blood clotting. They swell, become irregular in shape
and sticky and accumulate at the break of the vessel forming a platelet
plug to close the opening.
Preparation of Blood Smear
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1. Clean one of the fingers of your left hand with
a cotton soaked in alcohol.
2. Prick the tip of the cleaned finger with a sterile
needle and squeeze the finger tip to obtain a
drop of blood.
3. Place this drop of blood at one end of a clean
dry microscope slide.
4. Touch the drop of blood with the edge of dry
slide at an angle. The drop of blood
spreads along the sides of the slide.
5. Move the edge of the slide forward as shown
in Figure 18.11 to get a thin film of blood smear.
6. Leave the slide to dry. Pour 70% of alcohol
on the smear for fixing and dry again.
7. Stain the slide with Leishman’s blue or Wright’s
stain. After a minute or two, wash the slide
with water to remove the extra stain.
8. Dry the slide again and observe directly under
microscope.
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