Ultrastructure of the type-II pneumonocyte in lambs lung with special reference to the morphology of its inclusion bodies

The type-II pneumonocytes appeared as large rounded cells occupying the niches and the corners of the alveolar walls. They showed microvilli on their free surface and adjoining the type-1 cells through tight junctional areas. Their cytoplasm was rich with organoids. The most peculiar feature of this cell was the osmiophilic inclusion bodies which were thought to contain surfactant material or its precursor. Some of these inclusions appeared vacuolated or possessed homogeneous density. Others showed lighter osmiophilic material accumulated around a heavily osmiophilic core or they appeared lamellated. It seems possible that this morphological difference may well be related to the difference in the chemical constituents of these inclusion bodies