Salivary Glands
The glands of the oral cavity may be classified as serous, mucous or mixed according to the nature of their secretory product(s). The basic unit of structure is a saccular or tubular arrangement of mucous and serous secretory epithelial cells enclosing a lumen. One or several of these secretory units may empty into a small intralobular duct which joins others to form progressively larger intralobular, the interlobular ducts and finally the interlobar and excretory ducts. Portions of the intralobular ducts are involved in altering the ionic composition of the secretion. The glands are usually well vascularized, and are under control of the autonomic nervous system.
In H & E stained sections, the cells making up a mucous alveolus are columnar or pyramidal, with colorless or mildly basophilic non-granular cytoplasm. The nucleus is very flattened at the extreme base of the cell. Cell boundaries between adjacent cells are usually clear. In a serous acinus, the cell boundaries are not distinct, and the component pyramidal cells are usually smaller and more basophilic than those of mucous acini. The nucleus lies in the basal cytoplasm, but is oval or round and not flattened against the base of the cell. The apical cytoplasm is less abundant, and ideally contains an accumulation of acidophilic secretory granules although these are often lost in preparation.
Since the precise chemical nature of mucous and serous secretions of various organs can differ, mucous and serous acini from various locations are not necessarily identical in histological appearance, although the above descriptions include overall characteristics generally observed.
Secretory acini are scattered throughout the oral cavity, but three groups of acini form named anatomical entities, the three paired salivary glands. Of these, the parotids and submandibulars (submaxillaries) are more clearly defined as distinct organs, while the sublinguals are embedded within the tongue. The salivary glands produce about 1–2 liters of saliva per day