serous membrane A multi-tissue structure that is comprised of a secretory epithelial layer and a connective tissue layer.[TAO] FMA:9581 GAID:19 MESH:A10.615.789 TAO:0005425 UBERON:0000042 UMLS:C0036760 ZFA:0005425 a smooth membrane consisting of a thin layer of cells which excrete serous fluid. Serous membranes line and enclose several body cavities, known as serous cavities, where they secrete a lubricating fluid which reduces friction from muscle movement. Serosa is not to be confused with adventitia, a connective tissue layer which binds together structures rather than reducing friction between them. Each serous membrane is composed of a secretory epithelial layer and a connective tissue layer underneath. The epithelial layer, known as mesothelium, consists of a single layer of avascular flat nucleated cells (cuboidal epithelium) which produce the lubricating serous fluid. This fluid has a consistency similar to thin mucus. These cells are bound tightly to the underlying connective tissue. The connective tissue layer provides the blood vessels and nerves for the overlying secretory cells, and also serves as the binding layer which allows the whole serous membrane to adhere to organs and other structures.[WP] in FMA, SM = mesothelium + connective tissue. It excludes the cavity. Serous sac = SM + cavity. Note that the SM is a subtype of wall in FMA. multi-tissue structure that is comprised of a secretory epithelial layer (mesothelium) and a connective tissue layer. serosa tunica serosa uberon wall of serous sac mesoderm-derived structure cavity lining