The correct answer is option 4, the hypothalamus. The hypothalamus is a small but vital gland located in the brain. It plays a crucial role in maintaining temperature homeostasis, which is the body`s ability to regulate and maintain a stable internal temperature. The hypothalamus contains specialized cells called thermoreceptors that detect changes in body temperature. When the body gets too hot, the hypothalamus triggers sweating and dilates blood vessels to help cool down the body. On the other hand, when the body is too cold, the hypothalamus stimulates shivering and constricts blood vessels to conserve heat. In this way, the hypothalamus acts as the body`s thermostat, maintaining a constant temperature within a narrow range.