Surface architecture of the mucosal epithelium of the cat trachea: II. Structure and dynamics of the membranous portion

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Abstract
Bronchoscopic examination of anesthetized cats revealed that the trachea is capable of considerable change in caliber via lateral expansion of the membranous trachea. The morphological basis for this expansile capacity was determined by correlated light microscopy and scanning and transmission electron microscopy. The organization of the membranous trachea differs from that of the cartilaginous trachea. The mucosa is arranged in a series of longitudinal folds that open like an accordion when stretched laterally. These fold are not random, but appear to depend on rows of nonciliated, microvillusrich cells that form flexure lines in the surface epithelium. The mitochondria in such cell have a condensed configuration, indicating a high level of oxidative metabolism and suggesting that they may participate in transport processes that modify the luminal contents. Goblet cells, which are relatively sparse in the membranous trachea, have mitochondria in which the prominence of matrix granules and degree of mucus storage are inversely related. Mitochondrial morphology allows goblet cells that have discharged their mucin content to be readily distinguished from the microvillus‐rich cells, even when their luminal surfaces lie outside the thickness of a section.