part of part of endothelium outflow tract outflow tract endothelium MA:0000490 VHOG:0001524 It is assumed that during evolution, a circulatory system composed of the heart and endothelial tubular system first formed in vertebrates, medial smooth muscle then appeared for regulation of the system, and innervation of the muscle tissue took place. This sequence of development assumed for phylogenesis is actually realized in the ontogenetic processes.[well established][VHOG] UBERON:0004699 An endothelium that is part of a outflow tract [Automatically generated definition]. heart endothelium