Megakaryocyte (bone marrow, mouse)

Electron microscopy. A detail of the cytoplasm of a megakaryocyte (see inset) demonstrates distinctly a part of the intermediate zone subdivided by an interconnected tubular system (so-called demarcation membrane system or open canalicular system: OCS) that is in continuity with the cell surface. The cytoplasm contains few mitochondria (M), glycogen (G), free ribosomes, rough endoplasmic reticulum (R, and ↓), vacuoles and membrane-bound granules. The majority of the granules in stage of development is composed of the homogeneous electron-grey ones (1) with a dark centre (alpha-granula) variable in size. They contain among others platelet-derived growth factor, factor VIII (von Willebrand), thrombospondin, fibronectin, and fibrinogen. (2) indicate rodent virus particles that migrate along the OCS.