Which of the following systems includes skin, hair, and nails?

The integumentary system is the body's largest organ system and comprises the skin, hair, nails, and various associated glands. It serves several critical functions, including protection against environmental hazards, regulation of body temperature, sensation, and the synthesis of vitamin D. The skin acts as a barrier to pathogens, while hair and nails provide additional protection and have specific roles such as aiding in temperature regulation and enhancing sensory perception.

In contrast, the nervous system is primarily responsible for coordinating the body’s response to internal and external stimuli through signaling. The muscular system facilitates movement and is composed of muscle tissue, helping in tasks ranging from voluntary actions to involuntary processes. The skeletal system provides structural support, protection to vital organs, and works in conjunction with the muscular system to facilitate movement. None of these systems include skin, hair, and nails, confirming that the integumentary system is the correct answer.