Light and electron microscopic identification of elastic, elaunin and oxytalan fibers in human tracheal and bronchial mucosa

Summary

The elastic fiber system in the human tracheal and bronchial mucosa was studied by light and electron microscopy. Elastic fibers, elaunin fibers, and oxytalan fibers were discerned. These fibers were identified by means of their staining characteristics (elastica stains, methods for disulfide-groups) and on account of their fine structural morphology. Elastic fibers consist of elastin and few “elastic-fiber microfibrils”. The relative amount of elastin (compared to the amount of elastic-fiber microfibrils) is large in elastic fibers but small in elaunin fibers. Oxytalan fibers — by contrast — are pure bundles of microfibrils.

In the light microscope a well-defined elastic lamina separates the lamina propria and the submucosa of the normal mucous membrane. The elastic lamina is formed by coarse strands of longitudinally running elastic fibers. A delicate network of elastica-positive fibers is attached to the basement membrane of the epithelial layer (subepithelial elastic layer). A few of these elastica-positive fibers branch out, traverse the region of the thickened basement membrane, and insert into the basal lamina of the epithelium. A loose network of elastica-positive fibers is present both in the lamina propria and in the submucosa. Plates of cartilage, glandular epithelium, and bundles of smooth muscle cells are enveloped by delicate elastica-positive fibers.

Electron microscopy shows the lamina elastica to be predominantly composed of elastic fibers, whilst elaunin fibers from the subepithelial elastic layer. Fibers penetrating the thickened basement membrane of the epithelium are identified as oxytalan fibers. All three types of fibers are present throughout the lamina porpria and in the submucosa. Elaunin fibers and oxytalan fibers comprise the elastica-positive nets around glandular epithelium, smooth muscle bundles, and cartilage. The preferred location of oxytalan fibers (within the thickened basement membrane), elaunin fibers (subepithelial elastica-positive layer), and clastic fibers (lamina elastica) facilitates the comparison of light microscopic staining reactions and fine structural morphology of these fibers.