| Description |
Electron microscopy. These disc-shaped cells (2-4 m) without nucleus are derived from cytoplasmic fragments of the megakaryocyte. Free floating in the peripheral blood they develop thin extensions. They contain among others few mitochondria, smooth tubular systems, marginal localized microtubules, glycogen and different types of granula. The open canalicular system (OCS) is observed as light vacuoles (1) in between the granules. (2) peripheral bundle of microtubules. Homogeneous electron-dense delta granules (5) contain plasma-absorbed serotonin, calcium ions, ADP and ATP, etc., while the homogeneous electron-grey ones (lambda represents lysosomes (6). (3) mitochondria. (7, ↓ arrow) dense tubular system. On the other hand the electron-grey granules with a dark centre (4) (alpha-granula) are variable in size and shape and contain among others platelet-derived growth factor, factor VIII (von Willebrand), thrombospondin, fibronectin, fibrinogen. |
