How is epithelial tissue classified?

The tissues present in the human body are classified into four types: the epithelial tissue, the connective tissue, the muscle tissue, and the nervous tissue. The epithelium tissue is one of the primary tissue types present in the body that forms boundaries between different environments. The  epithelial tissue is responsible for the formation of a protective covering on the outer side of the organs, lining the inside of body cavities and also for the formation of various glands. Since this tissue completely surrounds the body organs, it is required to facilitate the passage of molecules across itself so that the organs can obtain adequate amounts of nutrition. Further, the tissue is responsible for carrying out the functions such as absorption and secretion of chemicals.