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Epithelium
Types of epithelium
Anatomical terminology[edit on Wikidata]

The vaginal epithelium is the the inner lining of the vagina and is composed of several cell layers that are not keratinized and whose superficial cell layers are flattened (multi-layered squamous epithelium). The cell layer directly adjacent to the basal membrane is called the basal layer, the middle cell layers as the middle or intermediate layer, and then the superficial layer. In the course of the reproductive cycle, the vaginal epithelium is subject to normal, cyclic changes, which are mainly due to the influence of estrogens . With the rise of estrogens before the follicle jump cell proliferation with increase of the cell layers, the cells mature and a partial cornification of the epithelial cells are triggered. Although hormonal changes take place in other sections of the female reproductive system, the vaginal epithelium reacts to much lower levels of hormones than, for example, the uterine lining. The structure of the vaginal epithelium is an indicator of estrogen levels. Some Langerhans cells and melanocytes are also present in the epithelium.

Development

The epithelium of the vagina originates from three different precursors during embryonic and fetal development. These are the vaginal squamous epithelium of the lower vagina, the columnar epithelium of the endocervix, and the squamous epithelium of the the upper vagina. The distinct origins of vaginal epithelium may impact the understanding of vaginal anomalies. Vaginal adenosis is the presence of other reproductive tissue within the muscular layer and epithelium of the vaginal wall. It often contains glandular tissue and appears as a raised, red surface.

Lytic cells and microbiota

Without estrogenic activity, the vaginal epithelium consists of only a few cell layers, and when sampled, only small round cells are obtained that originate directly from the basal layer (basal cells) or the cell layers (parabasal cells) immediately above it. The parabasal cells form a five- to ten-layer cell layer. They are slightly larger than the basal cells and multipotent cells, which are the starting point of epithelial cells located further on the surface. The parabasal cells can also differentiate into histiocytes or glandular cells. Estrogen influences the changing ratios of nuclear constituents to cytoplasm. As a result of cell aging, cells with shrunken, seemingly foamy cell nuclei (intermediary cells ) develop from the parabasal cells. These can be distinguished by means of the nuclear-plasma relation into "upper" and "deep" intermediate cells. Intermediate cells make abundant glycogen and store it. The further nuclear shrinkage and the formation of mucopolysaccharides are hallmarks of superficial cells. The mucopolysaccharides form a keratin-like cell scaffold. Fully keratinized cells without a nucleus are called 'floes'. Intermediate and superficial cells are constantly exfoliated from the epithelium. The glycogen from these cells is converted to sugars and then fermented by the bacteria of the vaginal flora to lactic acid. The the cells decompose (cytolysis) within a week's time. Cytolysis occurs only in the presence of glycogen-containing cells, that is, when the epithelium is degraded to the upper intermediate cells and superficial cells. In this process, the cytoplasm is primarily dissolved. The cell nuclei remain.

Cell characteristics

Cell junctions

The junctions between epithelial cells regulate the passage of molecules, bacteria and viruses by functioning as a physical barrier. The three types of structural adhesions between epithelial cells are: tight junctions, adherens junctions, and desmosomes. "Tight junctions (zonula occludens) are composed of transmembrane proteins that make contact across the intercellular space and create a seal to restrict paracellular diffusion of molecules across the epithelial sheet. Tight junctions also have an organizing role in epithelial polarization by limiting the mobility of membrane-bound molecules between the apical and basolateral domains of the plasma membrane of each epithelial cell. Adherens junctions (zonula adherens) connect bundles of actin filaments from cell to cell to form a continuous adhesion belt, usually just below the tight junctions."

Disease transmission

Sexually transmitted infections, including HIV are rarely transmitted across intact and healthy epithelium. These protective mechanisms are due to: frequent exfoliation of the superficial cells, low pH, and innate and acquired immunity in the tissue. Research into the protective nature of the vaginal epithelium is recommended and would help to design of topical drugs and microbicides.

History

Vaginal epithelium has been studied since 1910 by a number of histologists.

References

1. Up to 26 layers have been identified! See Pathology, American Society for Colposcopy and Cervical; Mayeaux, E. J.; Cox, J. Thomas (2011-12-28). Modern Colposcopy Textbook and Atlas. Lippincott Williams & Wilkins. ISBN 9781451153835.
2. Hans Friedrich Nauth (2014) (in German), Gynäkologische Zytodiagnostik (2. ed.), Stuttgart: Georg Thieme, p. 22, ISBN 978-3-13-131092-7 
3. ^ Karl Knörr, Henriette Knörr-Gärtner, Fritz K. Beller, Christian Lauritzen (2013) (in German), Geburtshilfe und Gynäkologie: Physiologie und Pathologie der Reproduktion (3. ed.), Berlin: Springer, pp. 24–25, ISBN 978-3-642-95584-6 
4. ^ Anderson, Deborah J.; Marathe, Jai; Pudney, Jeffrey (2014-06-01). "The Structure of the Human Vaginal Stratum Corneum and its Role in Immune Defense". American Journal of Reproductive Immunology. 71 (6): 618–623. doi:10.1111/aji.12230. ISSN 1600-0897.
5. ^ Pathology, American Society for Colposcopy and Cervical; Mayeaux, E. J.; Cox, J. Thomas (2011-12-28). Modern Colposcopy Textbook and Atlas. Lippincott Williams & Wilkins. ISBN 9781451153835.
6. "Vaginal Cytology: Introduction and Index". www.vivo.colostate.edu. Retrieved 2018-02-06.
7. ^ Reich, Olaf; Fritsch, Helga. "The Developmental Origin of Cervical and Vaginal Epithelium and Their Clinical Consequences". Journal of Lower Genital Tract Disease. 18 (4): 358–360. doi:10.1097/lgt.0000000000000023.
8. Domino, Frank J. (2010). The 5-Minute Clinical Consult 2011. Lippincott Williams & Wilkins. ISBN 9781608312597.
9. ^ Hans Friedrich Nauth (2014) (in German), Gynäkologische Zytodiagnostik (2. ed.), Stuttgart: Georg Thieme, p. 23, ISBN 978-3-13-131092-7 
10. Axel Wehrend (2010) (in German), Leitsymptome Gynäkologie und Geburtshilfe beim Hund, Stuttgart: Enke, p. 17, ISBN 978-3-8304-1076-8 
11. Nunn, Kenetta L.; Forney, Larry J. (2016-09-30). "Unraveling the Dynamics of the Human Vaginal Microbiome". The Yale Journal of Biology and Medicine. 89 (3): 331–337. PMC 5045142. PMID 27698617.
12. ^ Blaskewicz, Caitlin D.; Pudney, Jeffrey; Anderson, Deborah J. (2011-07-01). "Structure and Function of Intercellular Junctions in Human Cervical and Vaginal Mucosal Epithelia". Biology of Reproduction. 85 (1): 97–104. doi:10.1095/biolreprod.110.090423. ISSN 0006-3363.

• Vagina
• Human female reproductive system
• Mammal female reproductive system
• Women and sexuality
• Women's health
• Anatomy
• Gynaecology
• Epithelium