Megakaryocyte

Scheme electron microscopy. The megakaryocyte is derived from a pro-megakaryocyte which originates from splenic stem cells (CFU-S, colony forming units-spleen). The megakaryocyte is a giant polyploid cell (35-160 m) and contains a large multilobate nucleus (1). The perinuclear area shows Golgi areas (2), centrioles (3) and mitochondria (4). The granular population can be divided into homogeneous electron-dense delta granules (5) and homogeneous electron-grey ones (6) (lysosomes) and electron-grey ones with a dark center (7) (alpha granulum) (↓, arrows). Especially the intermediate zone shows many granules, glycogen (8), localized in cytoplasmic areas (ca. 2-4 m) that are subdivided by an interconnected tubular system (so-called demarcation membrane system (DMS, 9). These demarcation channels traverse the marginal zone enriched by cytoskeletal filaments (10) and are in continuity with the irregular cell surface. The dense tubular system is hardly visible.