Thrombocytes

At about 3 μm, thrombocytes are the smallest of the blood cells. They are created as the megakaryocyte disintegrates. Thrombocytes do  not have a nucleus. In streaming blood, thrombocytes have the shape of biconcave disks. In vascular endothelium, they attach to damaged structures and in this way seal the vessels. In the process, thrombocytes are activated,  change their shape and release secretory products 2 , 3 . One important sign of this activation is the formation of pseudopodia. The secretory products not only stimulate blood clotting, but also the subsequent processes of inflammation and repair. Electron micrographs usually show thrombocytes as spindle-shaped cells in cross-sections.

1 Peripheral bundle of microtubules

2 α-granules

3 Serotonin-containing granule (dense body)

Electron microscopy; magnification: × 27600

Thrombocytes

The equatorial section shows the array of organelles. Particularly prominent are the many α-granules 1 as well as the sections through the open tubular systems 2 . The latter consist of many tubules and vacuoles, which interconnect with each other and the extracellular space. This system influences the release of secretor y products from store d secretor y granules and is instrumental in the activation of thrombocytes. The peripheral layer also at-tracts attention. It contains a bundle of microtubules and somewhat thicker,  electron-dense tubules 3 , which are involve d in the regulation of the Ca++ concentration and the prostaglandin metabolism.

1 α-granules

2 Open system of canaliculi

3 Peripheral bundles of microtubules and electron-dense tubules

4 Mitochondrion

5 Golgi apparatus

6 Pseudopodium

Electron microscopy; magnification: × 27 600

References

Kuehnel, W.(2003). Color Atlas of Cytology, Histology, and Microscopic Anatomy. 4^th edition . Institute of Anatomy Universitätzu Luebeck Luebeck, Germany . Thieme Stuttgart · New York .