develops_from simple squamous epithelium mesoderm endothelium A layer of epithelium that lines the heart, blood vessels (endothelium, vascular), lymph vessels (endothelium, lymphatic), and the serous cavities of the body[MESH]. Simple squamous epithelium which lines blood and lymphatic vessels and the heart[FMA] BTO:0000393 CALOHA:TS-0278 EFO:0002548 FMA:63916 GAID:520 MESH:D004727 The term 'endothelium' has been either restricted to the continuous cell layer of the vertebrates, as we are assuming here, or applied to all the cells able to adhere to the luminal surface of the vascular basement membrane (Casley-Smith 1980) UBERON:0001986 UMLS:C0014257 endothelial galen:Endothelium uberon meso-epithelium