The properties of the megakaryocyte and the platelet may be briefly summarized as follows: a polyploid cell secretes, by an apocrine type mechanism, an anucleate element, endowed with strong autolytic and endocytic properties, and capable of performing contractile work. The latter element, specialized in this way, is prepared to play a major role in hemostatic reactions.

The relationships between the five properties considered for these elements are still largely unknown. A certain degree of polyploidy may conceivably be necessary for the megakaryocyte to secrete platelets, but the importance of polyploidy in its cytoplasmic maturation has recently been questioned.6 The influence of the absence of a nucleus on platelet metabolism, as well as on the endocytic properties of cells, is still a matter of controversy.97,98 Finally, there remains to be established the possible role of contraction in the release of platelet material,84 and molecular material degraded by lysosome action.

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