The maintains a steady internal environment for the body.

Hypothalamus

The hypothalamus maintains a steady internal environment for the body.  

The hypothalamus is a complex part of the brain that is located under the thalamus and above the pituitary gland. One of the main roles of the hypothalamus is to maintain homeostasis by keeping the human body in a balanced condition. The hypothalamus plays a part in various important functions of the body such as appetite and weight control, body temperature, emotions, sleep cycles, stress, blood pressure and levels of hormones in the circulation.

answer; i believe that the correct answer is (lung);

yes? sounds right, but you didn’t ask a question.