Histology of the major salivary glands.

Major salivary glands are characterized by the presence of numerous excretory units that consist of acini and a peculiar duct system. Under normal conditions, sebaceous glands are annexed to the duct system in the parotid and the submaxillary glands. The excretion of the saliva is assisted by the myoepithelial cells, which play an important role in the morphology of several kinds of salivary gland tumors. Interstitial lymphocytes give rise to the formation of lymph nodes in the parotid gland. Heterotopic salivary tissue is found in many locations throughout the head and neck. Age-induced variations and reactive changes include oncocyte proliferation, fatty infiltration, squamous and mucous metaplasia, hyperplasia, atrophy, and regeneration. An analysis of the normal salivary gland structure permits a morphogenetic approach to an understanding of the variability in histologic types of salivary gland tumors.