What is the function of epithelial tissue in our body?

Functions of epithelial tissue:

i. Epithelial tissue covers the body outside and lines the various cavities inside.ii. Epithelial tissue lines the hollow organs, body cavities, blood vessels and ducts.iii. Cells are rested on thin, doubled layered, non-cellular basement membrane.iv. Epithelial tissue has nerve supply of its own.v. Epithelial tissue is avascular (a = without, vascular = vessel), i.e. it lacks its own blood supply and hence, obtains nutrients which diffuse out of blood vessels.vi. Epithelial tissue has the power of division and regeneration. The old injured dead cells are sloughed off regularly and are replaced by new ones.

The higher you go up the less oxygen there is 

only b