serosa

Serosa, or serous membrane, is a smooth, slippery membrane that lines major body cavities and covers the external surfaces of many viscera. It consists of a layer of simple squamous epithelium (mesothelium) supported by connective tissue and secretes serous fluid, which lubricates movements of organs within the cavity. A serosa typically has two layers: a parietal layer that lines the cavity and a visceral layer that covers the organs, with a potential space between them containing serous fluid.

Major serous membranes include the peritoneum (abdominopelvic cavity), pleura (around the lungs), and pericardium (around the heart). The peritoneum forms specialized folds such as mesenteries and omenta and lines the abdominal cavity. Intraperitoneal organs are covered by visceral peritoneum on their external surfaces; retroperitoneal structures usually lack a complete serosa and are instead sheathed by adventitia or are only partially covered.

Developmentally, serosae arise from the coelomic mesothelium of the embryonic mesoderm, forming the serous membranes that enclose the ventral body cavities and their viscera.

Clinical relevance: serous membranes can become inflamed (serositis) or produce excess fluid (serous effusion) in disease; peritoneal inflammation can cause ascites and adhesions among viscera.