Heat Stroke

Thermostat in a sealed oven

Imagine your body is a kitchen oven with a thermostat (the hypothalamus) set to 98.6°F. Normally, the thermostat reads the air temperature, and if it gets too hot, it opens vents (skin blood vessels widen), turns on a cooling fan (sweating), and signals you to crack a window (find shade). In heat stroke, three things go wrong at once: the outside temperature keeps climbing (extreme heat or hard exercise generates heat faster than it escapes), the vents get blocked (dehydration, drugs, or humidity stop sweating and blood vessel widening from working), and then — here is the critical part — the thermostat itself gets cooked by the heat. Once the thermostat's wiring melts (the hypothalamus's cells are damaged above 104°F), it stops sending any cooling signals at all. The oven temperature keeps climbing with no brakes. Now every part of the oven — the walls, the heating elements, the insulation — gets damaged by the extreme heat. Proteins inside the oven's walls denature (unfold), seals crack (cell membranes become leaky), and the whole system fails. That is what happens to your brain, liver, muscles, and heart when core temperature exceeds 104°F.