What characteristic is unique to epithelial tissues?

Epithelial tissues are indeed characterized by their avascularity, meaning they do not contain blood vessels. Instead, they receive nutrients and oxygen through diffusion from the underlying connective tissues. This lack of direct blood supply is important for the function of epithelial tissues, which serves various crucial roles, including protection, absorption, and secretion.

In contrast, highly vascularized tissues, which are rich in blood vessels, are typically found in connective tissues rather than epithelial ones. While multiple cell types can be present in certain tissues, epithelial tissues generally consist of closely packed cells of similar types, often organized in layers. Innervation is a feature of many tissues, but the presence or absence of blood vessels stands out as a defining characteristic for epithelial tissues, emphasizing their unique physiological structure and function.