[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:07.42,0:00:12.35,Default,,0000,0000,0000,,The finish line's in sight\Nand you put on an extra burst of speed.
Dialogue: 0,0:00:12.35,0:00:15.48,Default,,0000,0000,0000,,As your legs pick up the pace,\Nyour breathing gets deeper,
Dialogue: 0,0:00:15.48,0:00:17.02,Default,,0000,0000,0000,,your heart pounds faster,
Dialogue: 0,0:00:17.02,0:00:20.53,Default,,0000,0000,0000,,and sweat pours over your skin.
Dialogue: 0,0:00:20.53,0:00:23.16,Default,,0000,0000,0000,,How does this substance\Nsuddenly materialize
Dialogue: 0,0:00:23.16,0:00:26.46,Default,,0000,0000,0000,,and what exactly is its purpose?
Dialogue: 0,0:00:26.46,0:00:29.78,Default,,0000,0000,0000,,There are a number of scenarios\Nthat can make us sweat:
Dialogue: 0,0:00:29.78,0:00:30.90,Default,,0000,0000,0000,,eating spicy foods,
Dialogue: 0,0:00:30.90,0:00:31.87,Default,,0000,0000,0000,,nervousness,
Dialogue: 0,0:00:31.87,0:00:33.59,Default,,0000,0000,0000,,and when we're sick.
Dialogue: 0,0:00:33.59,0:00:37.89,Default,,0000,0000,0000,,But exercise is probably the most familiar\Nand common.
Dialogue: 0,0:00:37.89,0:00:41.40,Default,,0000,0000,0000,,In that case, sweating happens \Nas a response to movement
Dialogue: 0,0:00:41.40,0:00:43.90,Default,,0000,0000,0000,,triggered deep inside your cells.
Dialogue: 0,0:00:43.90,0:00:47.09,Default,,0000,0000,0000,,As you increase your pace,\Nyour muscles work harder,
Dialogue: 0,0:00:47.09,0:00:49.85,Default,,0000,0000,0000,,increasing their demand for energy.
Dialogue: 0,0:00:49.85,0:00:52.69,Default,,0000,0000,0000,,A process called cellular respiration
Dialogue: 0,0:00:52.69,0:00:56.91,Default,,0000,0000,0000,,consumes glucose \Nand oxygen to form ATP,
Dialogue: 0,0:00:56.91,0:01:00.54,Default,,0000,0000,0000,,the energy currency of the cell.
Dialogue: 0,0:01:00.54,0:01:05.84,Default,,0000,0000,0000,,Much of this process takes place\Nin structures called mitochondria.
Dialogue: 0,0:01:05.84,0:01:07.28,Default,,0000,0000,0000,,The more you move,
Dialogue: 0,0:01:07.28,0:01:11.71,Default,,0000,0000,0000,,the harder mitochondria work\Nto supply your body with energy.
Dialogue: 0,0:01:11.71,0:01:14.34,Default,,0000,0000,0000,,All this work comes at a cost, though.
Dialogue: 0,0:01:14.34,0:01:18.57,Default,,0000,0000,0000,,As the cells break down the ATP,\Nthey release heat.
Dialogue: 0,0:01:18.57,0:01:23.00,Default,,0000,0000,0000,,The heat stimulates temperature sensors\Nthroughout your body.
Dialogue: 0,0:01:23.00,0:01:27.00,Default,,0000,0000,0000,,Those receptors detect the excess heat\Nbeing produced by your muscle cells
Dialogue: 0,0:01:27.00,0:01:30.71,Default,,0000,0000,0000,,and communicate that information\Nto the hypothalamus,
Dialogue: 0,0:01:30.71,0:01:32.99,Default,,0000,0000,0000,,which regulates body temperature.
Dialogue: 0,0:01:32.99,0:01:34.48,Default,,0000,0000,0000,,The hypothalamus responds
Dialogue: 0,0:01:34.48,0:01:37.82,Default,,0000,0000,0000,,by sending signals out through \Nthe sympathetic nervous system
Dialogue: 0,0:01:37.82,0:01:40.70,Default,,0000,0000,0000,,to the sweat glands in your skin.
Dialogue: 0,0:01:40.70,0:01:42.90,Default,,0000,0000,0000,,These are distributed all over the body
Dialogue: 0,0:01:42.90,0:01:46.79,Default,,0000,0000,0000,,with especially high concentrations\Non the palms of your hands,
Dialogue: 0,0:01:46.79,0:01:48.43,Default,,0000,0000,0000,,the soles of your feet,
Dialogue: 0,0:01:48.43,0:01:50.02,Default,,0000,0000,0000,,and on your head.
Dialogue: 0,0:01:50.02,0:01:52.84,Default,,0000,0000,0000,,When a sweat gland first receives\Nthe signal,
Dialogue: 0,0:01:52.84,0:01:56.12,Default,,0000,0000,0000,,the fluid surrounding the cells\Nin its coiled base
Dialogue: 0,0:01:56.12,0:01:59.99,Default,,0000,0000,0000,,contains high amounts \Nof sodium and chloride.
Dialogue: 0,0:01:59.99,0:02:03.53,Default,,0000,0000,0000,,The cells pump these ions\Ninto a hollow tube
Dialogue: 0,0:02:03.53,0:02:06.18,Default,,0000,0000,0000,,that runs through the sweat gland.
Dialogue: 0,0:02:06.18,0:02:09.76,Default,,0000,0000,0000,,Then, because it's saltier inside\Nthe tube than outside,
Dialogue: 0,0:02:09.76,0:02:13.56,Default,,0000,0000,0000,,water moves into the tube by osmosis.
Dialogue: 0,0:02:13.56,0:02:18.27,Default,,0000,0000,0000,,As what's called the primary secretion\Nbuilds up in the bottom of the tube,
Dialogue: 0,0:02:18.27,0:02:24.06,Default,,0000,0000,0000,,water pressure pushes it up\Ninto the long straight part of the duct.
Dialogue: 0,0:02:24.06,0:02:25.82,Default,,0000,0000,0000,,Before it seeps onto the skin,
Dialogue: 0,0:02:25.82,0:02:29.97,Default,,0000,0000,0000,,cells lining the tube will reclaim\Nas much salt as possible
Dialogue: 0,0:02:29.97,0:02:32.06,Default,,0000,0000,0000,,so the process can continue.
Dialogue: 0,0:02:32.06,0:02:35.15,Default,,0000,0000,0000,,The water in sweat absorbs \Nyour body's heat energy
Dialogue: 0,0:02:35.15,0:02:39.03,Default,,0000,0000,0000,,and then evaporates off of you\Nwhen it reaches the surface,
Dialogue: 0,0:02:39.03,0:02:43.50,Default,,0000,0000,0000,,which in turn lowers your temperature.
Dialogue: 0,0:02:43.50,0:02:46.49,Default,,0000,0000,0000,,This process, \Nknown as evaporative cooling,
Dialogue: 0,0:02:46.49,0:02:49.48,Default,,0000,0000,0000,,was an important adaptation \Nfor our ancestors.
Dialogue: 0,0:02:49.48,0:02:53.20,Default,,0000,0000,0000,,This cooling effect isn't only helpful\Nduring exercise.
Dialogue: 0,0:02:53.20,0:02:56.80,Default,,0000,0000,0000,,We sweat in many other scenarios, too.
Dialogue: 0,0:02:56.80,0:03:02.27,Default,,0000,0000,0000,,Eating particularly spicy food makes some\Npeople sweat profusely from their faces.
Dialogue: 0,0:03:02.27,0:03:06.77,Default,,0000,0000,0000,,That happens because spices trigger\Nthe same neural response in the brain
Dialogue: 0,0:03:06.77,0:03:12.60,Default,,0000,0000,0000,,that activates temperature receptors,\Nwhich usually respond to increased heat.
Dialogue: 0,0:03:12.60,0:03:15.94,Default,,0000,0000,0000,,Sweating is also part of \Nthe fight or flight response
Dialogue: 0,0:03:15.94,0:03:19.99,Default,,0000,0000,0000,,stimulated by stressful scenarios,\Nlike asking someone on a date
Dialogue: 0,0:03:19.99,0:03:22.29,Default,,0000,0000,0000,,or interviewing for a job.
Dialogue: 0,0:03:22.29,0:03:25.82,Default,,0000,0000,0000,,This happens because adrenaline\Nstimulates muscle activity
Dialogue: 0,0:03:25.82,0:03:28.75,Default,,0000,0000,0000,,and causes blood vessels to widen,
Dialogue: 0,0:03:28.75,0:03:33.48,Default,,0000,0000,0000,,two responses that increase heat\Nand trigger the sweating response.
Dialogue: 0,0:03:33.48,0:03:36.78,Default,,0000,0000,0000,,And sweating also occurs \Nwhen we get sick.
Dialogue: 0,0:03:36.78,0:03:39.52,Default,,0000,0000,0000,,When we're feverish,\Nwe sweat because infections
Dialogue: 0,0:03:39.52,0:03:43.28,Default,,0000,0000,0000,,stimulate the hypothalamus \Nto increase muscle activity,
Dialogue: 0,0:03:43.28,0:03:46.95,Default,,0000,0000,0000,,which in turn releases \Nmore energy as heat.
Dialogue: 0,0:03:46.95,0:03:49.02,Default,,0000,0000,0000,,That increases your overall temperature,
Dialogue: 0,0:03:49.02,0:03:54.48,Default,,0000,0000,0000,,a protective mechanism that makes your\Nbody less habitable for infectious agents.
Dialogue: 0,0:03:54.48,0:03:58.16,Default,,0000,0000,0000,,Like with running, sweating helps\Nyour body vent that heat.
Dialogue: 0,0:03:58.16,0:04:00.56,Default,,0000,0000,0000,,When the fever's over \Nor you've won your race,
Dialogue: 0,0:04:00.56,0:04:03.96,Default,,0000,0000,0000,,your temperature receptors \Nsense the decrease in heat
Dialogue: 0,0:04:03.96,0:04:08.47,Default,,0000,0000,0000,,and the hypothalamus brings \Nyour sweating response to an end.
Dialogue: 0,0:04:08.47,0:04:10.35,Default,,0000,0000,0000,,In some cases, like after a run,
Dialogue: 0,0:04:10.35,0:04:13.00,Default,,0000,0000,0000,,the hypothalamus also signals\Nto your body
Dialogue: 0,0:04:13.00,0:04:16.45,Default,,0000,0000,0000,,that you need to replenish the water\Nthat you've oozed out.
Dialogue: 0,0:04:16.45,0:04:19.41,Default,,0000,0000,0000,,So, when you're pushing yourself\Nto reach that next goal,
Dialogue: 0,0:04:19.41,0:04:23.39,Default,,0000,0000,0000,,you can think of sweat as your body's\Nvery own calibrator,
Dialogue: 0,0:04:23.39,0:04:26.19,Default,,0000,0000,0000,,enabling you to go that extra mile.