Cytology of normal mesothelial cells, with typical features.[1] Wright's stain
Histology of the peritoneal mesothelial lining, and underlying fibrous tissue. H&E stain.
PrecursorSomatopleuric mesenchyme
THH2., H3.
Anatomical terminology

The mesothelium is a membrane composed of simple squamous epithelial cells of mesodermal origin,[2] which forms the lining of several body cavities: the pleura (pleural cavity around the lungs), peritoneum (abdominopelvic cavity including the mesentery, omenta, falciform ligament and the perimetrium) and pericardium (around the heart).

Mesothelial tissue also surrounds the male testis (as the tunica vaginalis) and occasionally the spermatic cord (in a patent processus vaginalis). Mesothelium that covers the internal organs is called visceral mesothelium, while one that covers the surrounding body walls is called the parietal mesothelium. The mesothelium that secretes serous fluid as a main function is also known as a serosa.


Mesothelium derives from the embryonic mesoderm cell layer, that lines the coelom (body cavity) in the embryo. It develops into the layer of cells that covers and protects most of the internal organs of the body.


The mesothelium forms a monolayer of flattened squamous-like epithelial cells resting on a thin basement membrane supported by dense irregular connective tissue. Cuboidal mesothelial cells may be found at areas of injury, the milky spots of the omentum, and the peritoneal side of the diaphragm overlaying the lymphatic lacunae. The luminal surface is covered with microvilli. The proteins and serosal fluid trapped by the microvilli provide a slippery surface for internal organs to slide past one another.


Micrograph of benign mesothelial cells. Peritoneal wash. Pap stain.
Cytology of reactive mesothelium, with typical features. The main causes of reactive mesothelium are infection, trauma and cancer.[3] Wright's stain.

The mesothelium is composed of an extensive monolayer of specialized cells (mesothelial cells) that line the body's serous cavities and internal organs. The main purpose of these cells is to produce a lubricating fluid that is released between layers,[4] providing a slippery, non-adhesive, and protective surface to facilitate intracoelomic movement.

A layer of mesothelial cells grown in cell culture, featuring the typical "cobblestone" appearance.

The mesothelium is also implicated in the transport and movement of fluid and particulate matter across the serosal cavities, leukocyte migration in response to inflammatory mediators, synthesis of pro-inflammatory cytokines, growth factors, and extracellular matrix proteins to aid in serosal repair, and the release of factors to promote the disposition and clearance of fibrin (such as plasminogen). Mesothelial cells are capable of phagocytosis and are antigen-presenting cells. The secretion of glycosaminoglycans and lubricants may protect the body against infection and tumor dissemination.

Role in disease

See also


  1. ^ Image by Mikael Häggström, MD. Sources for mentioned features:
    - "Mesothelial cytopathology". Libre Pathology. Retrieved 2022-10-18.
    - Shidham VB, Layfield LJ (2021). "Introduction to the second edition of 'Diagnostic Cytopathology of Serous Fluids' as CytoJournal Monograph (CMAS) in Open Access". CytoJournal. 18: 30. doi:10.25259/CMAS_02_01_2021. PMC 8813611. PMID 35126608.
  2. ^ Victor P. Eroschenko (2008). Di Fiore's atlas of histology with functional correlations. Lippincott Williams & Wilkins. pp. 31–. ISBN 978-0-7817-7057-6. Retrieved 28 May 2011.
  3. ^ Image by Mikael Häggström. MD.
    Reference for findings and causes: "Reactive Mesothelial Cells". LabCE.
  4. ^ Leopold G. Koss; Myron R. Melamed (2006). Koss' diagnostic cytology and its histopathologic bases. Lippincott Williams & Wilkins. pp. 124–. ISBN 978-0-7817-1928-5. Retrieved 28 May 2011.