Histology of Parotid Gland\ Serous Salivary Gland Histology

What Are The Salivary glands?
Exocrine glands with ductal and acinar portions
Acinar portion is serous, mucinous or mixed
Acini are lined by luminal cells, which are enclosed by myoepithelial cells

Serous acini:
Dense, basophilic, PAS+ intracytoplasmic secretory granules containing amylase
Have central lumen that is rarely visible by H&E
Mucinous / mucous acini:
Larger than serous acini
Irregular pattern
Cells have abundant cytoplasm with clear mucin, well rounded basal nuclei and are arranged around empty lumina
Produce acid (positive for Alcian blue and mucicarmine) and neutral (PAS+) sialomucins
Myoepithelia cells:
Surround acini and intercalated ducts and mediate contraction
Have both epithelial and mesenchymal structures and functions and are important in the morphology of most salivary gland tumors
Myoepithelial cells surrounding intercalated ducts are more spindled and have fewer processes than those surrounding acini
Ducts:
Either intercalated, striated or interlobular, all with outer basal cells and inner luminal cells
Intercalated ducts have reserve cells that regenerate acinar tissue and terminal duct system
All epithelium is PAS+ (Pathol Int 1999;49:500)
Sebaceous glands are attached to parotid and submandibular ducts and are considered part of normal holocrine differentiation (holocrine secretions are produced within the cell, then are released into the lumen after rupture of the plasma membrane), based on the occurrence of salivary tumors with sebaceous differentiation (Am J Surg Pathol 1989;13:879)
Sebaceous type glands are mixed with salivary gland acini in 10 - 40% of normal parotid glands, often in periductal locations in interlobular ducts; either single, isolated sebaceous type cells within serous or mucinous salivary acini or as fully developed sebaceous glands
Salivary glands are made up of secretory acini (acini - means a rounded secretory unit) and ducts. There are two types of secretions - serous and mucous. The acini can either be serous, mucous, or a mixture of serous and mucous.

A serous acinus secretes proteins in an isotonic watery fluid.
A mucous acinuss secretes secretes mucin - lubricant

In a mixed serous-mucous acinus, the serous acinus forms a serous demilune around mucous acinus, as shown in the diagram.

The secretory units merge into intercalated ducts, which are lined by simple low cuboidal epithelium, and surrounded by myoepithelial cells.

These ducts continue on as striated ducts. These have a folded basal membrane, to enable active transport of substances out of the duct. Water resorption, and ion secretion takes place in the striated ducts, to make saliva hypotonic (reduced Na,Cl ions and increased carbonate, and potassium ions).
The striated ducts lead into interlobular (excretory) ducts, lined with a tall columnar epithelium.
The glands are divided into lobules by connective tissue septa. Each lobule contains numerous secretory units, or acini

.Parotid gland:
Serous acini only; contain numerous basophilic zymogen granules; nuclei are uniform, round and in the basal half of the cell
Intercalated ducts are long in comparison to striated ducts
Striated ducts are larger than intercalated ducts, 3 - 6x size of acinus; striations are due to folds in basal plasma membranes
Contains small lymph nodes near or within the gland, which arise from interstitial lymphocytes
Resembles pancreatic tissue but parotid gland had adipocytes and pancreatic tissue has islets and centroacinar cells
Submandibular gland:
Predominantly serous but also mucinous acini
Mucous cells are the most active and therefore the major product of the submandibular gland is saliva which is mucoid in nature
Sublingual gland:
Predominantly mucinous but also serous acini