Endothelial as an adjective is of or pertaining to the endothelium. while Epithelium as a noun is a membranous tissue composed of one or more layers of cells which forms the covering of most internal and external surfaces of the body and its organs; internally including the lining of vessels and other small cavities, and externally being the skin.
Part of speech: adjective
Definition: Of or pertaining to the endothelium.
Part of speech: noun
Definition: A membranous tissue composed of one or more layers of cells which forms the covering of most internal and external surfaces of the body and its organs; internally including the lining of vessels and other small cavities, and externally being the skin.
We hope you now know whether to use Endothelial or Epithelium in your sentence.