| Abstract: | The parabronchi of the Adelie penguin are endowed with wide atria forming pockets between a loose meshwork of bundles of smooth muscle cells lining the parabronchial lumen. The atrial epithelium is of variable thickness and bears numerous microvilli, which are overlain by/or embedded in sheets or whorls of lamellar material ("trilaminar substance", diameter of one lamella 8 ..10 nm) forming layers of very variable thickness. The cells contain either stacks or whorls of this material or roundish lamellated bodies, and are interconnected by desmosomal contacts as well as what presumably represent tight junctions. Underneath the epithelium and within the bundles of muscle cells regularly nerve fibres have been found. The diameter of the morphological air/blood barrier is about 165...210 nm in thin areas, excluding a 12...20 nm thick layer covering the luminal plasma membrane of the air capillary epithelium. The blood capillary endothelium ordinarily is markedly thicker (40...250 nm) than the air capillary epithelium (17...25 nm). The basal lamina between endo- and epithelium is a uniform structure measuring about 95...105 nm. The endothelial cells are interconnected by desmosomal and probably tight junctions. |
