The integumentary system is the body's largest organ system, composed primarily of the skin, but also including structures like hair, nails, and various glands. Its primary functions are protective, providing a physical barrier against pathogens, chemicals, and extreme temperatures. The structure consists of multiple layers, including the epidermis, which provides waterproof protection, and the dermis, which contains connective tissue, blood vessels, and nerves. Beyond protection, the system plays critical roles in thermoregulation, metabolic processes via vitamin D synthesis, and sensory function through associated nerve endings.