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#heatstroke #climate #climatechange #heat

"The Heat Will Kill You First" by Jeff Goodell

"On a hot day, the road to heatstroke looks like this: As soon as you step outside, your blood grows warmer, heated by the sun’s radiation and your own rising metabolism. Keeping your core body temperature at around 98 degrees—the happy place for humans—now requires work. Receptors in the preoptic area of your brain’s hypothalamus start to fire, telling your circulatory system to push more blood toward your skin, where the heat can be dissipated. Your sweat glands begin to pump salty liquid from a tiny reservoir at the base of the gland up to the surface of your skin. You sweat. As the sweat evaporates, the heat is carried away.

But the amount of heat your body can dissipate through sweat is limited. Your blood vessels dilate, trying to move as much overheated blood to the surface as possible. But if you don’t find a place to cool off, your core body temperature will rise quickly. And the harder you are working your muscles, the faster it will rise. Your heart pumps madly, trying to push as much blood as possible to your skin to cool off, but it can’t keep up. As your blood is shunted away from your core, your internal organs—your liver, your kidneys, your brain—become starved for blood and the oxygen it carries. You feel light-headed. Your vision dims and narrows. As your core body temperature rises to 101 degrees, 102 degrees, 103 degrees, you feel wobbly—and due to the falling blood pressure in your brain, you will likely pass out. This is in fact an involuntary survival mechanism, a way for your brain to get your body horizontal and get some blood to your head.

At this point, if you get help and can cool down quickly, you can recover with little permanent damage.

But if you fall onto the ground in a place that is exposed to the sun and lie there, the dangers increase. It’s like falling into a hot frying pan. Ground temperatures can be twenty to thirty degrees above air temperature. Your heart becomes desperate to circulate blood and find a way to cool down. But the faster your heart beats, the more your metabolism increases, which generates more heat, which causes your heart to beat even faster. It’s a lethal feedback loop: As your internal temperature rises, rather than cranking up your air conditioner, your body fires up your furnace. If you have a weak heart, that might be the end for you.

At a body temperature of 105 to 106 degrees, your limbs are convulsed by seizures. At 107 and above, your cells themselves literally begin to break down or “denature.” Cell membranes—the thin lipid walls that protect the inner workings of your cells—literally melt. Inside your cells, the proteins essential to life—the ones that extract energy from food or sunlight, fend off invaders, destroy waste products, and so on—often have beautifully precise shapes. The proteins start as long strands, then fold into helixes, hairpins, and other configurations, as dictated by the sequence of their components. These shapes define the function of proteins. But as the heat rises, the proteins unfold and the bonds that keep the structures together break: first the weaker ones, and then, as the temperature mounts, the stronger ones. At the most fundamental level, your body unravels.

At this point, no matter how strong or healthy you may be, your odds of survival are slim. The tiny tubes in your kidneys that filter out waste and impurities in your blood are collapsing. Muscle tissues are disintegrating. You develop holes in your intestines, and nasty toxins from your digestive tract flow into your bloodstream. Amid all this chaos, your circulatory system responds by clotting your blood, cutting off its flow to vital organs. This triggers what doctors call a clotting cascade, which uses up all the clotting proteins in your blood and, paradoxically, leaves you free to bleed elsewhere. Your insides melt and disintegrate—you are hemorrhaging everywhere."