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They contain serous acini, a grouping of serous cells that secrete serous fluid, isotonic with blood plasma, that contains enzymes such as alpha-amylase. Serous glands are most common in the parotid gland and lacrimal gland but are also present in the submandibular gland and, to a far lesser extent, the sublingual gland.
An acinus (/ ˈ æ s ɪ n ə s /; pl.: acini; adjective, acinar / ˈ æ s ɪ n ər / or acinous) refers to any cluster of cells that resembles a many-lobed "berry", such as a raspberry (acinus is Latin for "berry").
Each acinus consists of a single layer of cuboidal epithelial cells surrounding a lumen, a central opening where the saliva is deposited after being produced by the secretory cells. The three forms of acini are classified in terms of the type of epithelial cell present and the secretory product being produced - serous, mucoserous, and mucous.
Submucosal means that the actual gland resides in the connecting tissue below the mucosa. The submucosa is the tissue that connects the mucosa to the muscle outside the tube. The glands themselves are quite complex. The mucus factory is at the bottom, in the submucosa, it is composed of many little sacs (acini) where the mucus originates.
Serous glands secrete a watery, often protein-rich, fluid-like product, e.g. sweat glands. Mucous glands secrete a viscous product, rich in carbohydrates (such as glycoproteins), e.g. goblet cells. Sebaceous glands secrete a lipid product. These glands are also known as oil glands, e.g. Fordyce spots and meibomian glands.
Further, because the secretory cells are of both serous and mucous types, the submandibular gland is a mixed gland, and though most of the cells are serous, the exudate is chiefly mucous. It has long striated ducts and short intercalated ducts. [7] The secretory acinar cells of the submandibular gland have distinct functions.
After sectioning the serous cells resembled the common demilune shape, and were so named. [2] When the gland has this demilunar structure, it has mucoserous acini producing both serous and mucous secretions. Slice of submandibular gland. H&E staining, the structure of the red stained cytoplasm on the left is the serous demilunes.
The mucous salivary glands are similar in structure to the buccal and labial glands. They are found especially at the back part behind the vallate papillae, but are also present at the apex and marginal parts. In this connection, the anterior lingual glands require special notice.