Is the epithelium vascularized? How do nutrients and oxygen reach the epithelium? Why is this feature a significant evolutionary acquisition?
Epithelia are not vascularized (capillaries do not directly reach their cells). The epithelium exchanges substances by dispersal with the connective tissue situated under it.
As the epithelia are not vascularized minuscule skin injuries or scratches that occur all the time do not trigger bleeding and do not expose the blood to contamination from external agents. This is an significant protective method discovered by evolution.