Comparative biology of small granule cells and neuroepithelial bodies in the respiratory system. Short review.
Small granule epithelial cells and clusters of these cells termed neuroepithelial bodies are widely distributed in the respiratory systems of vertebrates, according to observations made in 24 species. The cells are thinly scattered along extrapulmonary and intrapulmonary airways from the larynx to the entrances of the alveoli. As a rule they escape notice unless demonstrated by special light microscopic methods including silver impregnation, PAS-lead hematoxylin staining, or immunocytochemical localization of a marker enzyme, neuron-specific enolase, all of which reveal small granule cells as a class. They are also recognizable in electron micrographs by their characteristic 1,000 to 3,000 A dense-core granules. These can differ in appearance from cell to cell within the same or different species, and small granule cells also can differ in their anatomical relationships or in their content of pharmacological agents like serotonin and peptide hormones bombesin, calcitonin, or leu-enkephalin. Current evidence thus clearly points out the heterogeneity of the class, although it is inadequate to characterize the presumptive endocrine or paracrine function of any of its members specifically. This brief review gives an idea of the range of animals surveyed for small granule cells as well as similarities and differences among cells from different species. It concludes with comments on practical methods for revealing these cells and guidance to sources of detailed information about them.
D000818:Animals; D004702:Endocrine Glands / Q000166:cytology; D004847:Epithelial Cells; D006098:Granulocytes / Q000166:cytology* / Q000648:ultrastructure; D006801:Humans; D008722:Methods; D012137:Respiratory System / Q000166:cytology* / Q000196:embryology; D014714:Vertebrates / Q000033:anatomy & histology*