Explain the role of epithelial tissue in the human body, providing examples of its different types and their specific functions.

Epithelial tissue forms the covering and lining of external and internal surfaces of the body. Its main roles include protection, secretion, absorption, filtration, and sensation. Examples include squamous epithelium (found in the lining of blood vessels and alveoli, facilitating diffusion), cuboidal epithelium (found in kidney tubules and glandular ducts, involved in secretion and absorption), columnar epithelium (found in the lining of the intestine, specialized for absorption and secretion), and stratified squamous epithelium (found in the skin, providing protection against abrasion).