The serous ones contain amylase. The mucous ones secrete sialomucins, and mixed units contain both serous and mucous components. Serous acini consist of pear-shaped groups of epithelial cells surrounded by a distinct basement membrane. The epithelial cells have a dense cytoplasm and a basal nucleus. The acini have a central lumen into which secretions flow from the epithelial cells.
Mucous acini are larger than serous acini.
The secretory cells have an abundant cytoplasm filled with clear mucous. The epithelial cells are pyramidal with a flattened basal nuclei. The former pattern is seen typically in the submandibular gland. The gland structure consists of a connective tissue stroma with blood vessels, nerves,lymphatics and ducts. The connective tissue septae divide the glands into lobules.