AN ULTRASTRUCTURAL-STUDY OF PULMONARY BRONCHIOLAR AND ALVEOLAR EPITHELIUM IN SHEEP

The cellular population lining the bronchiolar and alveolar epithelium of the lower respiratory tract of three clinically healthy, purebred Suffolk lambs of both sexes and 3-4 months old was studied using a tra nsmission-electron microscope. The epithelium of primary and secondary bronchioles consisted of four cell types: basal cells, intermediate c ells, ciliated cells, and non-ciliated (Clara) cells, whereas the epit helium of terminal and respiratory bronchioles consisted of only two k ind of cells: ciliated and Clara cells. The alveolar wall, including a lveolar ducts and saccules, was covered by type I and type II pneumocy tes. In addition, the presence of pulmonary intravascular macrophages was a constant in most of the alveolar capillaries. The morphologic ch aracteristics of all these cells are described in detail and discussed .