Image: submandibular salivary gland of a rat, stained with hematoxylin and eosin.
Serous acini: serous glandular cells show a pyramidal shape with a wide basal surface. Many granules are observed in the cytoplasm, which are secretory vesicles known as zymogen granules. The large amount of rough endoplasmic reticulum makes the basal part of the cell to stain darker with hematoxylin, while the upper part is more eosinophilic due to the high content of proteins.
Mucous acini: mucous cells are more rounded cells that store their products in the so-called mucin granules. They stain poorly with standard techniques, but are intensely colored with staining for carbohydrates, such as PAS staining.
Excretory ducts: they are tubes that gather the released products from the glandular cells. The walls of the excretory ducts are made up of one cell thick layer when they are close to the acini of the gland.
Connective tissue: the salivary gland is limited by a layer of connective tissue.