The skin is one of the best examples in the body for illustrating the correlation of form with function. Instead of looking at it from the viewpoint of its organization, this article takes each function and matches it with the cells meeting that need: keratinocytes for durability and cohesion for mechanical protection; epidermal intercellular substances to form an inpermeable barrier; melanocytes for ultraviolet protection; Langerhans cells for immune response; Merkle cells for sensation; hair follicles, sweat glands, extensive vascular supply, and adipose tissue for thermoregulation; and free and encapsulated nerve endings for sensation.