The role of megakaryocytes and tissue mast cells in the respiratory distress syndrome of adults.

The pathological role of megakaryocytes has been studied during adult respiratory distress syndrome (ARD) in the formation of intraalveolar oedema, microthrombi and hyaline membranes. The giant cells of the bone marrow are also thought to be involved in the development of peribronchial, perivascular and interalveolar oedemas. Heparin produced by tissue mast cells appears to counteract the clotting disturbances and to promote fibrinolysis in the acute phase of ARD. Vasoactive substances liberated from mast cells enhance oedema formation. Heparin has an influence on the lipid metabolism of type II pneumocytes. During regeneration the stimulating effect of heparin on fibrosis becomes predominant in the connective tissue ground substance. No fundamental morphological difference was found between ARD and the infantile respiratory distress syndrome.