Mesothelium Health Dictionary

n. the tissue that covers the external surface of the body and lines hollow structures (except blood and lymphatic vessels). It is derived from embryonic ectoderm and endoderm. Epithelial cells may be flat and scalelike (squamous), cuboidal, or columnar. The latter may bear cilia or brush borders or secrete mucus or other substances (see goblet cell). The cells rest on a common basement membrane, which separates epithelium from underlying *connective tissue. Epithelium may be either simple, consisting of a single layer of cells; stratified, consisting of several layers; or pseudostratified, in which the cells appear to be arranged in layers but in fact share a common basement membrane (see illustration). See also endothelium; mesothelium. —epithelial adj.... epithelium

(serosa) a smooth transparent membrane, consisting of *mesothelium and underlying elastic fibrous connective tissue, lining certain large cavities of the body. The *peritoneum of the abdomen, *pleura of the chest, and *pericardium of the heart are all serous membranes. Each consists of two portions: the parietal portion lines the walls of the cavity, and the visceral portion covers the organs concerned. The two are continuous, forming a closed sac with the organs essentially outside the sac. The inner surface of the sac is moistened by a thin fluid derived from blood serum, which allows frictionless movement of organs within their cavities. Compare mucous membrane.... serous membrane

(synovium) the membrane, composed of mesothelium and connective tissue, that forms the sac enclosing a freely movable joint (see diarthrosis). It secretes the lubricating synovial fluid.... synovial membrane