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Myoepithelial cell

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MYOEPITHELIAL CELLS: STRUCTURE, FUNCTION & IDENTIFICATION

Author: Sanketh DS, MDS

INTRODUCTION

The secretory cells present in salivary glands are of two types, called serous and mucous cells. These secretory cells, also called acinar cells are housed in secretory end pieces. The secretory end pieces are continuous with the main excretory duct of the salivary gland through intermediary ducts. The lumen of the end pieces open into the intercalated duct, which is continuous with the striated duct, which in turn opens into the excretory duct of the salivary gland. Also note that the ducts are lined by ductal cells. Now, the secretory end pieces and intercalated ducts are associated with stellate shaped contractile cells called the myoepithelial cells. They are located between the basal lamina and the secretory or ductal epithelial cells. They are also called “basket cells” because they look like a basket holding a secretory unit. The myoepithelial cells have a central body with cytoplasmic extensions embracing the acinar cells. These cells however, are more fusiform shaped and have lesser cytoplasmic extensions when associated with the ductal cells. The cells are called “myo-epithelial” due to the fact that they are primarily derived from epithelial cells but exhibit certain characteristics of smooth muscle cells.

STRUCTURE

Myoepithelial cells have a central body with 4-8 cytoplasmic processes. These processes may further branch out to secondary and tertiary processes thus securely hugging the acinar cells. They have a flattened nucleus in their cell body with cytoplasmic organelles around it. The plasma membrane of the cell appears to run parallel to the membrane of the adjacent acinar or ductal cell. The plasma membrane of the myoepithelial cell has small invaginations called caveolae. The myoepithelial cell is attached to the adjacent acinar or ductal cell through desmosomal junctions. It has to be remembered that myoepithelial cells have smooth muscle like properties but are primarily epithelial cells having an ectodermal origin. They have features of smooth muscle cells in that they have contractile actin and myosin filaments. However, they also harbour cytokeratin filaments and desmosomal junctions, both characteristic of epithelial cells.

FUNCTIONS

1. The main function of the myoepithelial cell is to contract and help squeeze out secretory products from the secretory end pieces to the ducts and finally to the oral cavity.
2. The repeated contractions of the myoepithelial cell helps in maintaining patency of the ducts.
3. Myoepithelial cells have also been postulated to maintain the structural integrity of the secretory end pieces and the cell polarity of the secretory acinar cells.
4. Interestingly, studies report that myoepithelial cells have a protective function in that they may secrete proteins that may have anti-cancer effects, like tumor-suppressor activity and anti-angiogenic activity. Tumor suppressor activity refers to inhibition of growth of cancerous cells while the anti-angiogenic activity refers to the inhibition of proliferation of blood vessels, which may be a source of nutrition for cancer cells.
5. Another controversial and speculated function of the myoepithelial cell, is the transport of metabolites through the multiple membrane infoldings called the caveolae.

IDENTIFICATION

Myoepithelial cells can be identified through numerous stains and methods like hematoxylin and eosin stains, fluorescent stains, special stains like silver staining and immunohistochemical markers like α-SMA, CK-14, CK-17,calponin, integrin and p63.

REFERENCES

Chitturi RT, Veeravarmal V, Nirmal RM, Reddy BV. Myoepithelial Cells (MEC) of the Salivary Glands in Health and Tumours. J Clin Diagn Res. 2015 Mar;9(3):ZE14-8.

Shah AA, Mulla AF, Mayank M. Pathophysiology of myoepithelial cells in salivary glands. J Oral Maxillofac Pathol. 2016 ;20(3):480-490.

Nanci A. Tencate’s Oral Histology. Development, Structure and Function. 8th ed. Elsevier;2013.

Kumar GS. Orban’s Oral Histology and Embryology.13th ed. Elsevier;2011.

Avery JK.Oral development and Histology.3rd ed. Thieme Medical Publishers;2002.

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