Epithelial tissue functions in

This type of tissue covers most exposed areas of the body and lines the body cavities such as blood and lymph vessels, the digestive tract, and glands. These cells function in:

Protection - they form a barrier that is special for their need (like keeping in liquids or allowing the passage of certain materials). Skin cells protect against foreign invasion and permit homeostasis (keeping the internal environment at a certain desired level). This includes keeping certain substances in their proper place in the body, such as blood in vessels and gastric juice in the digestion system.

Structure / support - they line cavities keeping everything in order.

Secretion - certain cells have the task of secretion, these are found scattered in the appropriate epithelial layers (often times in ducts which are in glands).