Which of the following variables is commonly regulated by negative feedback to maintain homeostasis?

• A. Core body temperature
• B. Hair color
• C. Blood type
• D. Kidney stone formation

Answer: (A)

Negative feedback loops keep body conditions near a stable set point, with core body temperature as a classic example. The hypothalamus acts like a thermostat, sensing small shifts from the normal temperature. If the core gets too hot, the body responds by increasing heat loss—sweating and vasodilation of skin blood vessels—to cool down. If the core gets too cold, warming mechanisms kick in—shivering and vasoconstriction—to raise or conserve heat. These responses push the temperature back toward the set point, reducing the original deviation.

Hair color and blood type are determined by genetics and remain constant, not adjusted by feedback to maintain a body-wide balance. Kidney stone formation is a pathological process related to urine chemistry and does not function as a normal homeostatic variable controlled by negative feedback.