The parotid glands are the largest of the major salivary glands. They are composed of alveoli containing only serous secretory cells. Adipose tissue often occurs in the parotid gland and may be one of its distinguishing features. The facial nerve (cranial nerve VII) passes through the parotid gland; large cross sections of this nerve, often found in routine H&E sections of the gland, may also be of help in identifying the parotid. Mumps, a viral infection of the parotid gland, can damage the facial nerve.
Figure 1, parotid gland, human, H&E X160.
The parotid gland in the human is composed entirely of serous acini (A) and their ducts. However, numerous adipose cells (AC) are usually distributed throughout the gland. Both the serous acini and their duct system in the parotid gland are comparable in structure and arrangement to the same components in the submandibular gland. Within the lobule, the striated ducts (StD) are readily ob served. They exhibit a simple columnar epithelium. The intercalated ducts are smaller; at the low magnification of this figure, they are difficult to recognize. A few intercalated ducts (ID) are indicated. The lower portion of the figure reveals an excretory duct (ED) within a connective tissue septum (CT). The epithelium of this excretory duct exhibits two layers of nuclei and is either pseudostratified or, possibly, already true stratified epithelium.
Figure 2, parotid gland, monkey, glutaralde-hyde-osmium tetroxide fixed, H&E X640.
The serous cells are optimally preserved in this specimen and reveal their secretory (zymogen) granules. The granules appear as fine dot-like objects within the cytoplasm. The acinus in the upper right of the figure has been cut in cross section and reveals the acinar lumen (AL). The small rectangle drawn in the acinus represents an area comparable to the electron micrograph shown as Figure 15.24. The large acinar profile to the left of the striated duct (StD) shows that the acini are not simple spheres but, rather, irregular elongate structures. Because of the small size of the acinar lumen and the variability in sectioning an acinus, the lumen is seen infrequently.
A cross-sectional profile of an intercalated duct (ID) appears on the left of the micrograph; note its simple cuboidal epithelium. A single flattened nucleus is present at the top of the duct and may represent one of the myoepithelial cells that are associated with the beginning of the duct system as well as with the acini (A). The large duct occupying the center of the micrograph is a striated duct (StD). It is composed of columnar epithelium. The striations (S) that give the duct its name are evident. Also of significance is the presence of plasma cells (PC) within the connective tissue surrounding the duct. These cells produce the immunoglobulins taken up and resecreted by the acinar cells, particularly secretory IgA (slgA).
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