Epithelial tissues usually occur as structurally minor, but functionally important components of complex organs in the animal body. Some of the most important functions of epithelial tissue are as follows: absorption, secretion, transcellular transport (of molecules across epithelium), protection barrier (e.g. the skin), selective permeability (controlling movement of material) and detection of sensations (via hair cells, taste buds and the retina). As you can see, this type of tissue can be very diverse in both form and function. The cells are closely packed and can be arranged into one or more layers. Epithelial tissue typically lines the different surfaces of the body. It also contributes to forming solid organs and glands.