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Here is an essay on ‘Blood Platelets’ for class 8, 9, 10, 11 and 12. Find paragraphs, long and short essays on ‘Blood Platelet’ especially written for school and college students.
Essay on Blood Platelets
Essay Contents:
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- Essay on the Introduction to Blood Platelets
- Essay on the Components of Blood Platelet
- Essay on the Functions of Blood Platelets
- Essay on the Properties of Blood Platelets
- Essay on the Methods of Counting of Blood Platelets
Essay # 1. Introduction to Blood Platelets:
Platelets are non-nucleated round or oval, biconvex discs having various sizes and covered by unit membrane. The average size is 2.5 µ. But bigger forms (4 – 5µ) are also seen. In ordinary blood film the platelets are generally not seen separately but in clumps. If ant agglutinant (EDTA) is applied, in the blood prior to drawing of film then the same can be seen separately in light microscope.
In light microscope generally two components of platelets are seen in the stained slide. One is the clear ground substance—the hyalomere (hyalos=glass, meros=part) that is stained very faintly and the other is the deeply stained central portion—the chromatomere or granulomere.
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Electron microscopic studies of platelets stained with glutaraldehyde followed by osmium tetroxide reveal additional components other than two components mentioned above. It is also claimed that the surrounding membrane of each platelet is covered by a thin film of carbohydrate.
In electron microscope the hyalomere is seen to consist of homogeneous fine granular materials. These hyalomeres in the periphery of platelets were also found to contain microtubules and microfilaments.
The microtubules probably give the ovoid structure of platelets and the microfilaments are presumably associated with microtubules. The microfilaments contain thrombosthenin which can contract like actin and myosin in muscle. This contractile element—the thrombosthenin is responsible for change of the shape of platelets.
Similarly, under electron microscope, the chromatomere is seen to contain numerous components.
Essay # 2. Components of Blood Platelet:
These components (Fig. 4.14) are as follows:
i. Alpha Granules:
These granules are oval or sometimes round in shape and having diameter, 0.2 µ and length 0.3 µ to 0.4 µ. These granules are often seen enclosed in a membrane. A rounded dense osmophilic area is often present in these granular matrices of the organelle.
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The function of α-granules is still uncertain. It is claimed that it has got lysosomal function which is important in platelet release reaction and aggregation, in clot resolution or in the platelet’s phagocytic capacity. Whether these granules are the sources of the platelet factor-3 are not clear.
ii. Mitochondria:
These are 2-3 in number and are clearly seen in a thin section of platelets.
iii. Sydersomes:
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These are iron-containing (Ferritin) vesicles. These are not seen very frequently.
iv. Very Dense Granules (Serotonin-Containing Granules):
These types of granules have been demonstrated by Silver & Gardner in rabbit’s platelets. These granules have got diameter 0.05 µ to 0.13 µ and are surrounded by a unit membrane. These granules have been described to contain serotonin. Because these granules are osmophilic and as serotonin (5-HT) is also highly osmophilic. Furthermore following treatment with reserpine, the relative concentration of the osmophilic granules in these organelles is decreased.
v. Glycogen Granules:
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These granules are also distributed in certain parts of the platelets.
vi. Ribosomes:
These are generally seen in newly formed platelets.
vii. Systems of Tubules and Vesicles:
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These are of two types. One is the surface-connecting system and the other is the dense-connecting system. The surface-connecting systems communicate with the surface of platelets and are concerned with phagocytosis. The dense-connecting system originates from the Golgi apparatus of the megakaryocyte. This system does not communicate with the surface of the platelets.
The average life of platelets is about 5 to 9 days. They are destroyed in the spleen and other reticulo-endothelial cells.
Essay # 3. Functions of Blood Platelets:
i. Initiate Blood Clotting:
When blood is shed, the platelets disintegrate and liberate thromboplastin which activates prothrombin into thrombin.
ii. Repair Capillary Endothelium:
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While in the circulation, the platelets adhere to the damaged endothelial lining of the capillaries and thus bring about a speedy repair. It is known that the capillary walls, being very delicate, are easily damaged and unless these weak spots are quickly mended, the vessels will break at these spots and capillary bleeding will take place. When the platelet count falls (below 50,000 per cu. mm) such capillary bleeding occurs.
iii. Haemostatic Mechanism:
This process seems to play by the dual functions of platelets such as agglutination and coagulation. The cessation of blood flow from ruptured blood vessels takes place through simultaneous coagulation and agglutination by platelets.
iv. Hasten Clot Retraction:
Speed of clot retraction (syneresis) is directly proportional to the number of platelets present and this retraction process is dependent upon the thrombosthenin (contractile protein of platelets) in presence of ATP and magnesium ions.
v. When Platelets Disintegrate, 5-Hydroxytryptamine and Histamine are Liberate:
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5-hydroxytryptamine (5-HT) has vasoconstrictor effect and helps in haemostatic mechanism.
vi. Contain Some Substances which are like ABO Blood Antigens:
Platelets may be agglutinated by specific antisera and in the presence of complement, lysis may occur.
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Purpura:
In this disease there is diminution of platelets in the blood. Haemorrhage occurs beneath the skin and mucous membrane. The appearance of lesions varies with the type of purpura, the duration of lesions, and the acuteness of the onset.
The colour is first red, becoming gradually darker, then purple, fading to a brownish yellow. It may result in permanent pigmentation or it may disappear in course of 2 or 3 weeks but the damaged capillary endothelium is not repaired. The coagulation time remains normal but the bleeding time is prolonged. The clot does not retract.
Essay # 4. Properties of Blood Platelets:
Not exactly known. Platelets possess protein and a considerable amount of phospholipid, much of which seems to be cephalin.
Characteristic properties are:
(a) Sticking to water-wettable surface or otherwise rough surface (injured or diseased endothelium, etc.),
(b) Easy clumping, and
(c) Easy disintegration and thus liberation of thrombokinase.
Total Number and its Variations:
The average number of platelets present per cubic mm of blood is about 250,000 to 450,000. Fairly rapid changes in number take place from day to day and even from one part of the day to another. Roughly speaking, those physiological conditions, which alter the total count of leucocytes, also alter the platelet count in the same direction.
Essay # 5. Methods of Counting of Blood Platelets:
For avoidance of clumping, an antiagglutinating agent, EDTA (ethylenediamine tetra-acetic acid) is generally used during counting of platelets. This can be done in ordinary light microscope by direct or indirect method. In ordinary method, a drop of antiagglutinating substance is poured over the clear surface of the skin and a pin puncture is made through the drop.
The blood that comes out is mixed up with the antiagglutinating agent and an ordinary blood film is made through it. The platelet count is made along with the number of R.B.C. present in each field. It is counted as the number of platelets present per 100 R.B.C. in each field. If the erythrocyte count per cubic mm is made then the value of platelets number can be worked out from the above ratio.
In direct method the platelet count is made by counting the same along with R.B.C. in counting chamber. In this method, measured amount of blood and measured amount of antiagglutinant along with a dye are taken in the pipette and are thoroughly mixed. The platelets and R.B.C. present are counted in a counting chamber.
