Final answer:
The nervous system is the key player in responding to environmental input to maintain homeostasis. It works in conjunction with other systems like the integumentary system to regulate the body's internal environment in response to external changes.
Step-by-step explanation:
The system that gets input from the outside environment and responds to protect homeostasis is the nervous system. Sensory receptors within the nervous system detect changes in the environment, such as temperature, light, sound, and send this information to the brain. The brain then processes the information and sends signals to other body systems to make the necessary adjustments to maintain homeostasis. For example, if the body needs more oxygen, the respiratory system will increase breathing rate, and the circulatory system will work to deliver more oxygen to cells in need.
The integumentary system, which includes the skin, also plays a role in maintaining homeostasis by serving as a barrier against environmental changes, helping to regulate body temperature, and enabling sensory perception.