endothelium
noun [ C ] medical specialized uk/ˌen.dəʊˈθiː.li.əm/ us/ˌen.doʊˈθiː.li.əm/ endothelia /ˌen.dəʊˈθiː.li.ə/ /ˌen.doʊˈθiː.li.ə/
内皮,内皮层
the thin layer of cells that cover the inside walls of the blood vessels, heart and some other body parts)