Cytodifferentiation of the Salivary glands

Once the events surrounding the morphogenesis of the salivary glands are well under way, the cells of the glands begin to be specified. This cytodifferentiation is initially begun around the time of the beginning of epithelial morphogenesis. In the mouse submandibular gland cytodifferentiation begins at about the 16th embryonic day. For the parotid gland it does not begin until several days after birth. The submandibular gland also differentiates late, around the 17th embryonic day, as it is the last of the three major salivary glands to begin morphogenesis. As cytodifferentiation begins, the epithelial cells begin to change shape (Handbook of Physiology, 1989). The early cells of the glands differentiate into the specialized cells of the acini, and become columnar in shape, changing from the primitive cuboidal shape. The acini cells combine to make up the terminal end of the salivary gland, the lobule, and secrete materials into the differentiated stalk cells which empty into the oral cavity.

These acini are exocrine glands which secrete a mucin glycoprotein and glutamine/glutamic acid-rich proteins when they function in the submandibular gland (Moreira, 1991). The differentiated acinar cells of the parotid glands are serous cells, producing a watery fluid with globular proteins and digestive enzymes. The acini of the sublingual gland has both serous and mucous secretions; mucous excretions are viscous since they are filled with mucin. These cells types arise separately at embryonic day 18 (Moreira, 1991). The secretions of the acinar cells are accounted for by the amplification of the Golgi bodies ability to process the newly made secretory proteins (Handbook of Physiology, 1989).

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