mésothelium

The mésothelium (mesothelium) is a single layer of specialized squamous epithelial cells that lines the body’s serous cavities and internal organs. It forms the pleura (lining the lungs and thoracic cavity), the peritoneum (abdominal cavity), the pericardium (heart sac), and related structures such as the tunica vaginalis.

Mesothelial cells arise from the embryonic mesoderm and create a continuous, semi-permeable surface. Their apical surfaces are often microvillus-rich and they rest on a thin basement membrane supported by connective tissue. Intercellular junctions allow both barrier function and selective transport.

Principal functions include reducing friction between moving organs by secreting a lubricating serous fluid, facilitating the transport of cells and particles across the cavity, regulating fluid and solute exchange, and contributing to local immune responses and tissue repair. Mesothelial cells secrete cytokines, growth factors, and extracellular matrix components and can undergo phenotypic changes during inflammation or wound healing.

Clinically, the mesothelium is notable as the site of malignant mesothelioma, a cancer most commonly linked to asbestos exposure. Other conditions include serositis, effusions, and postoperative adhesions. Diagnosis and research use histological appearance and immunohistochemical markers such as calretinin, WT1, and cytokeratins to distinguish mesothelial cells from other epithelia.