Heat Illness and Hypothermia

Your body's furnace with a broken thermostat

Imagine your body is a house with a furnace (metabolism), a thermostat (hypothalamus), and windows that open and close (skin blood vessels and sweat glands). Normally the thermostat reads the temperature inside and adjusts—opening windows to dump heat when it's too hot, closing them and turning up the furnace when it's too cold—to keep the house at exactly 37°C. In heat illness, the outside is so hot (or you're exercising so hard your furnace is roaring) that even wide-open windows and maximum sweating can't cool you down fast enough; the temperature inside keeps climbing past the safe zone because the heat pouring in exceeds what can escape. In hypothermia, the outside cold or a broken thermostat (from alcohol or brain injury) means the windows stay open or the furnace can't kick on, so heat drains out faster than the body can replace it, and the temperature plummets. Either way, once the inside temperature drifts too far from 37°C, the walls and wiring of the house (your cells) start to malfunction: proteins cook and tangle in heat, or enzymes freeze and stop working in cold, until the whole system fails.