A lolling tongue is not a cute accessory; it is the front end of a cooling system that lets many dogs keep running long after humans slow down. While sweat glands handle most excess heat in humans, canine skin contributes little to cooling. Instead, dogs turn their mouth, tongue and upper airways into an evaporative plant sized for motion.
During panting, rapid breaths move large volumes of air over the moist surface of the tongue and through the nasal turbinates, driving evaporative cooling and convective heat loss. Warm blood from working muscles and a rising core temperature flows through dense capillary networks in these tissues, where heat diffuses out and water molecules carry it away as vapor. This supports a high metabolic rate during running, because the heat generated by muscle contraction can be exported quickly enough to avoid dangerous hyperthermia.
The lungs further scale this system. Each panting cycle pulls cooler ambient air deep into the respiratory tree, increasing the gradient for heat transfer between blood and air. Blood vessels near the brain also benefit: selective cooling in nasal and cranial regions helps protect neural tissue even as the body works hard. Limb mechanics then add leverage: long legs, elastic tendons and efficient gait reduce wasted energy, meaning less heat must be dissipated for every meter covered.
