Figure 185

Photomicrograph of a section of the trachea and esophagus, a. This specimen, obtained from an elderly individual, shows the relationship between the trachea and the esophagus at the base of the neck. The cartilaginous tracheal rings, which keep the trachea patent, have a C-shaped appearance. The cartilage gap, where the trachea is adjacent to the esophageal wall, is spanned by a fibroelastic membrane. It contains the trachealis muscle and numerous seromucous glands. In this specimen, the tracheal ring has been transformed, in part, to bone, a process that occurs in aging. The darker-staining material represents number of mucous cells increases during chronic irritation of the air passages.

• 1Brush cells have the same general features as those described for the respiratory epithelium of the nasal cavity (Fig. 18.9a). They are columnar cells that bear blunt microvilli. The basal surface of the cells is in synaptic contact with an afferent nerve ending (epitheliodendritic synapse). Thus, the brush cell is regarded as a receptor cell.

• Small granule cells are respiratory representatives of the general class of enteroendocrine cells of the gut and gut derivatives (Fig. 18.9b). Their presence is explained by the development of the respiratory tract and lungs from an evagi-nation of the primitive foregut. Small granule cells usually occur singly in the trachea and are sparsely dispersed among the other cell types. They are difficult to distinguish from basal cells in the light microscope without special techniques such as silver staining, which reacts with the granules. The nucleus is located near the basement membrane; the cytoplasm is somewhat more extensive than that of the smaller basal cells. With the transmission electron cartilage, whereas the lighter-staining material has been replaced by bone tissue. The very light areas (arrows) are marrow spaces. X3.25. b. This high-magnification photomicrograph shows an area of the tracheal ring that has partially transformed into bone. The top of the micrograph shows the tracheal mucosa and submucosa. Below is part of the tracheal ring. In this particular region, however, a substantial portion of the cartilage has been replaced by bone tissue and marrow. The bone tissue exhibits typical lamellae and osteocytes. The cartilage tissue, in contrast, exhibits nests of chondrocytes. xlOO.

microscope (TEM), a thin, tapering cytoplasmic process is sometimes observed extending to the lumen. Also, with the TEM, the cytoplasm exhibits numerous, membrane-bounded, dense-core granules. In one type of small granule cell the secretion is a catecholamine. A second cell type produces polypeptide hormones such as serotonin, calcitonin, and gastrin-releasing peptide (bombesin). Some small granule cells appear to be innervated. The function of these cells is not well understood. Some are present in groups in association with nerve fibers, forming neuroepithelial bodies, which are thought to function in reflexes regulating the airway or vascular caliber. • Basal cells serve as a reserve cell population that maintains individual cell replacement in the epithelium. Basal cells tend to be prominent because their nuclei form a row in close proximity to the basal lamina. Although nuclei of other cells reside at this same general level within the epithelium, they are relatively sparse. Thus, most of the nuclei near the basement membrane belong to basal cells.

goblet eel Is

0 0

Post a comment