Salivary gland histology

• The submandibular gland is a compound tubuloalveolar gland.
• It is surrounded by a capsule of moderately dense connective tissue, from which septa divide the gland into lobes and lobules.
• The secretory endpieces consist of a more or less spherical mass of cells called an acinus (pl. acini). 
• The cells of the acini appear triangular in sections, with their apex directed toward the lumen, and their base resting on a basement membrane. 
• They secrete their product in a merocrine fashion into the lumen. 
• Contractile cells called myoepithelial cells or basket cells lie between the basement membrane and the plasma membrane of the secretory cells. 
•  Myoepithelial cells posess many actin-containing microfilaments, which squeeze on the secretory cells and move their products toward the excretory ducts. They can sometimes be identified in standard histological preparations.
• Acini can be either serous or mucous.
•  The secretion of serous cells is thin, watery and proteinaceous. 
• Serous cells have a rounded nucleus and secretory granules in their cytoplasm. 
• They are joined near their apical surfaces by junctional complexes. 
• Mucous cells secrete a viscous, glycoprotein-rich product, which is stored as mucinogen granules.
•  The nuclei are typically flattened against the base of the cells (unless the cells have just discharged their contents, in which case they look more like serous cells). 
• Mucous cells typically look pale and empty in standard histological sections, because their granules are lost during preparation.
•  Its mucous acini are quite frequently capped with a serous demilune, a crescent of serous cells around one or more of their surfaces.

Types of Ducts

• There are three types of ducts in the submandibular gland: intercalated, secretory (aka striated) and excretory ducts.
•  Intercalated ducts are slender ducts continuous with the terminal acini, and lined with flat, spindle-shaped cells. They secrete bicarbonate ion into and absorb chloride ion from the acinar product. 
• Secretory ducts have eosinophilic cuboidal to columnar cells with basal striations. These result from infoldings of the basal membranes in which are found many mitochondria. Secretory ducts resorb sodium and secrete potassium
• Both intercalated and secretory ducts are found within the parenchyma of the gland and are therefore intralobular ducts.
• The largest ducts are the excretory ducts. They are found in the connective tissue septa, and are therefore interlobular ducts. 
• They ultimately connect with the oral cavity. 
• Their epithelium is variable, it can be simple cuboidal, stratified cuboidal, stratified columnar or pseudostratified. 
• Near the oral cavity, it becomes stratified squamous.
•  Excretory ducts do not change the secretory product.

Credit:http://www.courseweb.uottawa.ca/medicine-histology/english/gastrointestinal/Salivary.htm