Description: Scheme electron microscopy.
These disc-shaped anucleate cells (2-4 mm) are derived from cytoplasmic fragments of the megakaryocyte. They contain few mitochondria, a canalicular system, a smooth tubular system, marginal localized microtubules, glycogen and different types of granula.
A circumferential band of these microtubules (1, arrows) is responsible for the characteristic shape of the platelet.
The canalicular system presents as interconnecting vacuoles that open at the surface (*).
Electron-grey d granules (5) contain plasma-absorbed serotonin, calcium ions, ADP and ATP etc., while the a-granula (2) variable in size and shape, contain among others platelet-derived growth factor, factor VIII (von Willebrand), thrombospondin, fibronectin, fibrinogen.
(6): Dense tubular system.
Background: In a clotting process due to adherence to collagen exposed receptors for factor VIII platelets change their shape becoming spherical and develop numerous long thin cytoplasmic processes that interlink with other platelets. The granular contents are released via the open canalicular system and the clotting cascade is activated due to adhesion of other platelets under the influence of ADP, calcium ions etc.
Keywords/Mesh: blood, bone marrow, platelet, megakaryocyte, histology, electron microscopy, POJA collection