Which statement defines homeostasis?

• A. The body's tendency to maintain a stable internal environment.
• B. The process of blood circulation.
• C. A method of muscle contraction.
• D. The study of organs.

Answer: (A)

Homeostasis is the body's tendency to keep its internal environment stable even when external conditions change. It works through continuous monitoring of variables such as temperature, pH, fluid balance, and glucose levels, with sensors and control centers coordinating effectors like sweat glands, muscles, kidneys, or hormone responses to bring things back to normal. This regulation happens mainly through negative feedback, creating a dynamic balance that keeps cells and organs functioning properly. For example, when body temperature rises, cooling responses kick in; when it drops, warming responses activate. The other statements describe a specific process (like moving blood), a mechanism (muscle action), or a field of study (anatomy/physiology), rather than the overall balancing act that defines homeostasis.