THROMOPOIESIS (FORMATION OF PLATELETS)

Development of Thrombocytes (Platelets)

Formation of Thrombocytes (Platelets)

Development of Thrombocytes (Platelets)

Thrombocytes or platelets are formed by budding from the cytoplasm of megakaryocytes in the bone marrow and occasionally in the lungs. 

About 3000 to 4000 platelets are produced from a single megakaryocyte.

The cytological characteristics of platelets and their progenitors are as follows: 

1. Megakaryoblast 

Size 16 to 25 microns. 

Nucleus It is lobulated with one or two diploid nucleoli, dark purple or blue finely reticulated chromatin. The nucleus to cytoplasm ratio is approximately 9:1. 

Nucleoli Indistinct 2-5. 

Cytoplasm Scanty, greyish blue in colour with occasional vacuole. 

2. Promegakaryocyte (Basophilic megakaryo cyte) 

Size 20-45 microns. 

Nucleus Coarse, lobulated with purplish chromatin network. The nucleus to cytoplasm ratio is approximately 9:2. 

Nucleoli Indistinct 1 or 2. 

Cytoplasm Slightly polychromatic (purplish pink), with occasional fine azurophilic granules. 

3. Megakaryocyte 

This is the largest of all the blood cells with pleomorphic uninuclear structure, occasionally with multilobular pattern. Size 30-90 microns.

3. Megakaryocyte 

This is the largest of all the blood cells with pleomorphic uninuclear structure, occasionally with multilobular pattern. 

Size 30-90 microns. 

Nucleus Red purple, coarse clumped chromatin with multi lobulated pattern. The nucleus to cytoplasm ratio varies because the nucleus may occupy most of the cell in some cases or may be eccentric with abundant cytoplasm in others. 

Nucleoli Varies from 0-1 but very indistinct. 

Cytoplasm Usually abundant, light purple blue filled with fine purple granules. It frequently shows irregular pseudopodal projections representing platelets in the process of transformation.

4. Thrombocytes (platelets) Size 2-4 microns. 

Nucleus None. 

Nucleoli None. 

Cytoplasm Pale blue with pink-red azurophilic granules.

Functions of Platelets