The histology and fine structure of glands in the rat respiratory tract

Abstract

The structure of rat respiratory glands has been investigated by light and electron microscopy. The glands exhibited a tubulo-acinar organization. Individual secretory units were composed of serous tubules or serous demilunes and mucous tubules with narrow lumens at the blind end (proximally), and of mucous ducts with wide lumens which opened to the tracheal lumen distally. Near the junction of the duct with the trachea, mitochondria-rich cells and a few ciliated cells were interspersed with mucous cells. It was found that the histology as well as the ultrastructure of the secretory product of these gland cells varied depending upon the location of the glands in the airway. For this reason, the glands of the epiglottis, larynx and trachea have been described separately. Epiglottal glands consisted of many mucous tubules, a few serous elements and an occasional mucous duct. Laryngeal glands contalned many serous and mucous tubules and a few mucous ducts. Tracheal glands were composed of serous tubules, a few mucous tubules and prominent bucous ducts. Serous tubule cell granules formed a uniform population within a cell profile but varied in cells of the epiglottis, compared with those of the larynx and trachea. Granules in mucous tubule cells differed from those of serous cells. Mucous cell granules also appeared uniform within a single cell but differed from cell to cell and at different levels of the respiratory tract. A particular granule type was predominant at each level. Cells of mucous ducts differed somewhat from those of mucous tubules and comprised two general secretory cell populations. Proximal mucous duct cells contained abundant granules that generally resembled those of mucous tubule cells but were localized in two areas of the cytoplasm. Dilated cisternae of rough endoplasmic reticulum with a bizonal content similar in density of zones seen in mature granules further characterized proximal mucous duct cells. The distal mucous duct cell generally contained sparse apical granules and lacked dilated rough endoplasmic reticulum.

Microscopic Anatomy of the Lower Respiratory System of the African Giant Pouched Rat (Cricetomys gambianus, Waterhouse 1840)

“…Histology of the lower respiratory system in other rodents such as the laboratory rat (Spicer et al, 1982;Choi et al, 2000;Widdicombe et al, 2001), hamster (Kennedy et al, 1978), squirrel (Nakakuki, 1979) and guinea pig (Kliment et al, 1972) have been described in detail. However, such description in the African Giant pouched rat is lacking.…”

Immunocytochemical demonstration of quantitative differences in the distribution of lysozyme in human airway secretory granule phenotypes

“…A number of studies [4,6,13,16,17] have reported that the secretory granules of bronchial serous acini show a marked variation in electron-density. According to Spicer et al [21,22], human and rat airway serous cells are not only characterized by spherical electron-dense SG typical of serous cells, but smaller elongated granules and periodatereactive small bodies of cylindrical shape were also frequently identified. According to lchikawa and lchikawa [9,10], who compared standard and rapid freezing fixation and from the present results, we can suggest that SG2-and SG4-phenotypes are representative of mature stages of the serous granules.…”

“…The present study confirms the presence of lysozyme in the submucosal serous cells of the human upper [23,24] and lower [5] respiratory tract and their absence from the submucosal mucous cells. In all the studies mentioned and in reviews on the histochemistry of respiratory epithelium and submucosal glands [21], the morphological heterogeneity of the serous cell secretory granules and irregular distribution of lysozyme within these different granules is reported, although no quantitation of the lysozyme-staining serous cell SG has been carried out. It has already been reported by De Water et al [6] and Puchelle et al [18] that the bronchial antileukoproteinase (also called bronchial inhibitor), a protein which like lysozyme participates in lung defense, is not distributed uniformly in the various SG-phenotypes of the human bronchial glands.…”

Lung, Pleura, and Mediastinum

“…The glands are present predominantly in the intercartilagenous submucosa on the ventral aspect and their density decreases towards the bronchial bifurcation. There is some strain variability in the distribution of glands as Sprague-Dawley and Brown Norway rats have submucosal glands throughout, whereas F344 rats have none in the lower trachea and bronchi (Widdicombe et al, 2001;Ohtsuka et al, 1997;Spicer et al, 1982). The tracheal epithelium is supported by fibrous connective tissue, smooth muscle, and cartilage rings, but the rings disappear soon after the airways enter the lung.…”