Evidence for a theory of physical fragmentation of megakaryocytes, implying that all platelets are produced in the pulmonary circulation.

The mathematical description of a fragmentation mechanism which leads to log normal volume distribution is applied to platelet production from megakaryocyte cytoplasm. Large cytoplasmic fragments and whole megakaryocytes are released from the bone marrow into the circulation. Physical fragmentation of the cytoplasm occurs in the pulmonary circulation producing the observed heterogeneity of platelet volume. Experimental evidence is used to provide quantitative verification that physical fragmentation is the process which produces all platelets. With this theory the currently accepted concept of the predesignation of the platelet population by the demarcation membrane system in megakaryocyte cytoplasm becomes redundant.