Development of secretory units of mouse submandibular gland

Summary The fine structure of the secretory units of the mouse submandibular gland was studied according to the developmental sequence. The embryonic submandibular gland consists of terminal tubules and ducts. Myoepithelium is associated only with the terminal tubules, and the cells of the primary intercalated ducts show characteristics of the young striated duct cells. The major changes shortly after birth consist of: 1) opening of the secretory lumina, 2) increasing rough ER and its altered configuration, 3) dilatation of Golgi cisternae and 4) changes in the granular structure. These findings suggest that the salivary secretion first occurs after birth, and acinar differentiation or transformation of the secretory cells of the terminal tubules is induced and profoundly affected by the commencement of the secretory activity. In the intercalated ducts this process is somehow inhibited, and the granular cells found in the adult can be considered as the remnants of the secretory cells of the terminal tubules.