[Endocrine cells of the APUD-system in the human lung (electron microscopy characteristics)]

Lungs of 4 human fetuses (11-, 13-, 22-, 28-week-old), of 1 stillborn and of 3 mature persons, operated in connection with pulmonary cancer, have been investigated. In the fetal lungs apudocytes and neuroepithelial bodies (NEB) have been revealed. The apudocytes differ from each other by structure and size of endocrine granules. In the 11-week-old fetus P1 cells with two types of granules occur most often. Among P1 cells there are several subgroups, differing in their granule dimensions. P2 apudocytes possess granules of one type with a round core and a narrow rim of cytoplasm. P3 cells are characterized with still larger granules, a very dense core and a narrow rim. In large bronchi some groups are found, consisting of two and more endocrine cells of all three types. In the lungs of the 13-week-old fetus P1 cells are defined and a new type of cells, that contain homogenous granules, characterizing by their small size. In 22 weeks of development in the intrapulmonary bronchi apudocytes with granules specific for Ec-cells are found. NEB consists of cells and islands, possessing polymorphous granules. Various types of apudocytes are defined in large bronchi of the 22-week-old fetus. In the stillborn infant apudocytes in the lung are found very seldom. In lung of the mature persons the morphology of apudocytes is unitypical. Thus, during embryogenesis and after birth there are variable types of endocrine cells and NEB.