The parotid salivary glands produce serous secretions. The synthesized products are accumulated and stored in secretory (zymogen) granules of cytoplasm #1, #2, #3 until a neural or humoral stimulus to secrete is received by such a cell. The granules are concentrated in the apical cytoplasm near lumina of an acinus that is a secretory unit of the gland. Some cisterns of rough endoplasmic reticulum #1, #2, where secretory products are actually synthesized, are seen in the perinuclear space. Golgi apparatus is also usually found there; it is a site to form the secretory granules. The acinar lumen is quite narrow. Simultaneous release of a large secretory volume into this limited space of the acinar lumen leads to secretions exerting pressure in the initial portions of glandular ducts. The pressure is maintained by a flow of fluids and ions from the intercellular (interstitial) space #1, #2 into the acinar lumen.

Small granules, whose contents are not so dense, belong to the machinery of minor secretion. They are necessary to provide sites of zymogen granule attachment and to let them easily fuse with the plasma membrane.