Final answer:
The integumentary system, which includes the skin, hair, and nails, protects the body and helps maintain homeostasis; it is also the body's largest organ system.
Step-by-step explanation:
The body system that includes the skin is called the integumentary system. This system comprises not only the skin but also hair and nails, which are accessory structures. The integumentary system is vital for protecting the body, sensing the environment, and helping to maintain homeostasis. The skin serves as a barrier, shielding internal structures and fluids from harmful microorganisms and toxins. Furthermore, it is the body's largest organ system, encompassing approximately 16 percent of an adult's body weight and covering an area of 1.5 to 2 m².