What body system includes skin, hair, nails, sweat glands, and sebaceous glands?

The integumentary system is the correct answer because it encompasses all components mentioned in the question: skin, hair, nails, sweat glands, and sebaceous glands. This system serves several vital functions, including protection against environmental hazards, regulation of body temperature, and sensation. The skin acts as a barrier protecting internal organs and tissues, while hair and nails provide additional protection and play roles in sensory functions.

In contrast, the muscle system is primarily responsible for movement and maintaining posture, the endocrine system involves hormone production and regulation, and the skeletal system provides structural support and facilitates movement through the connections between bones and muscles. Thus, each of those other systems handles different biological functions that do not include the structures specified in the question. The integumentary system is uniquely designated to encompass the protective and regulatory characteristics attributed to the skin and its associated components.