[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:07.71,0:00:12.48,Default,,0000,0000,0000,,It starts with a tickle in your throat\Nthat becomes a cough.
Dialogue: 0,0:00:12.48,0:00:14.48,Default,,0000,0000,0000,,Your muscles begin to ache,
Dialogue: 0,0:00:14.48,0:00:15.96,Default,,0000,0000,0000,,you grow irritable,
Dialogue: 0,0:00:15.96,0:00:17.92,Default,,0000,0000,0000,,and you lose your appetite.
Dialogue: 0,0:00:17.92,0:00:20.82,Default,,0000,0000,0000,,It's official: you've got the flu.
Dialogue: 0,0:00:20.82,0:00:24.10,Default,,0000,0000,0000,,It's logical to assume that this\Nmiserable medley of symptoms
Dialogue: 0,0:00:24.10,0:00:27.29,Default,,0000,0000,0000,,is the result of the infection\Ncoursing through your body,
Dialogue: 0,0:00:27.29,0:00:29.19,Default,,0000,0000,0000,,but is that really the case?
Dialogue: 0,0:00:29.19,0:00:31.93,Default,,0000,0000,0000,,What's actually making you feel sick?
Dialogue: 0,0:00:31.93,0:00:37.40,Default,,0000,0000,0000,,What if your body itself\Nwas driving this vicious onslaught?
Dialogue: 0,0:00:37.40,0:00:42.26,Default,,0000,0000,0000,,You first get ill when a pathogen\Nlike the flu virus gets into your system,
Dialogue: 0,0:00:42.26,0:00:44.92,Default,,0000,0000,0000,,infecting and killing your cells.
Dialogue: 0,0:00:44.92,0:00:47.48,Default,,0000,0000,0000,,But this unwelcome intrusion \Nhas another effect:
Dialogue: 0,0:00:47.48,0:00:51.23,Default,,0000,0000,0000,,it alerts your body's immune system\Nto your plight.
Dialogue: 0,0:00:51.23,0:00:56.59,Default,,0000,0000,0000,,As soon as it becomes aware of infection,\Nyour body leaps to your defense.
Dialogue: 0,0:00:56.59,0:01:00.86,Default,,0000,0000,0000,,Cells called macrophages charge in\Nas the first line of attack,
Dialogue: 0,0:01:00.86,0:01:05.50,Default,,0000,0000,0000,,searching for and destroying the viruses\Nand infected cells.
Dialogue: 0,0:01:05.50,0:01:10.55,Default,,0000,0000,0000,,Afterwards, the macrophages release\Nprotein molecules called cytokines
Dialogue: 0,0:01:10.55,0:01:11.100,Default,,0000,0000,0000,,whose job is to recruit
Dialogue: 0,0:01:11.100,0:01:16.99,Default,,0000,0000,0000,,and organize more virus-busting cells \Nfrom your immune system.
Dialogue: 0,0:01:16.99,0:01:19.30,Default,,0000,0000,0000,,If this coordinated effort \Nis strong enough,
Dialogue: 0,0:01:19.30,0:01:23.41,Default,,0000,0000,0000,,it will wipe out the infection\Nbefore you even notice it.
Dialogue: 0,0:01:23.41,0:01:27.19,Default,,0000,0000,0000,,But that's just your body setting\Nthe scene for some real action.
Dialogue: 0,0:01:27.19,0:01:29.92,Default,,0000,0000,0000,,In some cases, viruses spread further,
Dialogue: 0,0:01:29.92,0:01:32.54,Default,,0000,0000,0000,,even into the blood and vital organs.
Dialogue: 0,0:01:32.54,0:01:35.01,Default,,0000,0000,0000,,To avoid this sometimes dangerous fate,
Dialogue: 0,0:01:35.01,0:01:38.24,Default,,0000,0000,0000,,your immune system must launch\Na stronger attack,
Dialogue: 0,0:01:38.24,0:01:41.29,Default,,0000,0000,0000,,coordinating its activity with the brain.
Dialogue: 0,0:01:41.29,0:01:43.71,Default,,0000,0000,0000,,That's where those unpleasant symptoms\Ncome in,
Dialogue: 0,0:01:43.71,0:01:45.76,Default,,0000,0000,0000,,starting with the surging temperature,
Dialogue: 0,0:01:45.76,0:01:46.83,Default,,0000,0000,0000,,aches and pains,
Dialogue: 0,0:01:46.83,0:01:48.31,Default,,0000,0000,0000,,and sleepiness.
Dialogue: 0,0:01:48.31,0:01:51.17,Default,,0000,0000,0000,,So why do we experience this?
Dialogue: 0,0:01:51.17,0:01:53.52,Default,,0000,0000,0000,,When the immune system is under\Nserious attack,
Dialogue: 0,0:01:53.52,0:01:55.91,Default,,0000,0000,0000,,it secretes more cytokines,
Dialogue: 0,0:01:55.91,0:01:57.100,Default,,0000,0000,0000,,which trigger two responses.
Dialogue: 0,0:01:57.100,0:02:02.02,Default,,0000,0000,0000,,First, the vagus nerve, which runs through\Nthe body into the brain,
Dialogue: 0,0:02:02.02,0:02:05.34,Default,,0000,0000,0000,,quickly transmits the information\Nto the brain stem,
Dialogue: 0,0:02:05.34,0:02:09.42,Default,,0000,0000,0000,,passing near an important area\Nof pain processing.
Dialogue: 0,0:02:09.42,0:02:12.99,Default,,0000,0000,0000,,Second, cytokines travel through\Nthe body to the hypothalamus,
Dialogue: 0,0:02:12.99,0:02:15.92,Default,,0000,0000,0000,,the part of the brain responsible\Nfor controlling temperature,
Dialogue: 0,0:02:15.92,0:02:16.90,Default,,0000,0000,0000,,thirst,
Dialogue: 0,0:02:16.90,0:02:17.79,Default,,0000,0000,0000,,hunger,
Dialogue: 0,0:02:17.79,0:02:18.92,Default,,0000,0000,0000,,and sleep,
Dialogue: 0,0:02:18.92,0:02:20.56,Default,,0000,0000,0000,,among other things.
Dialogue: 0,0:02:20.56,0:02:22.08,Default,,0000,0000,0000,,When it receives this message,
Dialogue: 0,0:02:22.08,0:02:24.43,Default,,0000,0000,0000,,the hypothalamus produces\Nanother molecule
Dialogue: 0,0:02:24.43,0:02:28.100,Default,,0000,0000,0000,,called prostaglandin E2,\Nwhich gears it up for war.
Dialogue: 0,0:02:28.100,0:02:32.76,Default,,0000,0000,0000,,The hypothalamus sends signals\Nthat instruct your muscles to contract
Dialogue: 0,0:02:32.76,0:02:35.66,Default,,0000,0000,0000,,and causes a rise in body temperature.
Dialogue: 0,0:02:35.66,0:02:37.40,Default,,0000,0000,0000,,It also makes you sleepy,
Dialogue: 0,0:02:37.40,0:02:40.74,Default,,0000,0000,0000,,and you lose your appetite and thirst.
Dialogue: 0,0:02:40.74,0:02:43.90,Default,,0000,0000,0000,,But what's the point of all of these\Nunpleasant symptoms?
Dialogue: 0,0:02:43.90,0:02:45.61,Default,,0000,0000,0000,,Well, we're not yet sure,
Dialogue: 0,0:02:45.61,0:02:48.83,Default,,0000,0000,0000,,but some theorize that they aid\Nin recovery.
Dialogue: 0,0:02:48.83,0:02:51.52,Default,,0000,0000,0000,,The rise in temperature can slow bacteria
Dialogue: 0,0:02:51.52,0:02:54.59,Default,,0000,0000,0000,,and help your immune system\Ndestroy pathogens.
Dialogue: 0,0:02:54.59,0:02:58.64,Default,,0000,0000,0000,,Sleep lets your body channel\Nmore energy towards fighting infection.
Dialogue: 0,0:02:58.64,0:03:03.31,Default,,0000,0000,0000,,When you stop eating, your liver can\Ntake up much of the iron in your blood,
Dialogue: 0,0:03:03.31,0:03:06.27,Default,,0000,0000,0000,,and since iron is essential \Nfor bacterial survival,
Dialogue: 0,0:03:06.27,0:03:09.23,Default,,0000,0000,0000,,that effectively starves them.
Dialogue: 0,0:03:09.23,0:03:12.67,Default,,0000,0000,0000,,Your reduced thirst makes \Nyou mildly dehydrated,
Dialogue: 0,0:03:12.67,0:03:14.96,Default,,0000,0000,0000,,diminishing transmission through sneezes,
Dialogue: 0,0:03:14.96,0:03:15.80,Default,,0000,0000,0000,,coughs,
Dialogue: 0,0:03:15.80,0:03:16.70,Default,,0000,0000,0000,,vomit,
Dialogue: 0,0:03:16.70,0:03:17.90,Default,,0000,0000,0000,,or diarrhea.
Dialogue: 0,0:03:17.90,0:03:20.81,Default,,0000,0000,0000,,Though it's worth noting that if you don't\Ndrink enough water,
Dialogue: 0,0:03:20.81,0:03:23.62,Default,,0000,0000,0000,,that dehydration can become dangerous.
Dialogue: 0,0:03:23.62,0:03:26.26,Default,,0000,0000,0000,,Even the body's aches \Nmake you more sensitive,
Dialogue: 0,0:03:26.26,0:03:29.96,Default,,0000,0000,0000,,drawing attention to infected cuts\Nthat might be worsening,
Dialogue: 0,0:03:29.96,0:03:32.92,Default,,0000,0000,0000,,or even causing your condition.
Dialogue: 0,0:03:32.92,0:03:34.73,Default,,0000,0000,0000,,In addition to physical symptoms,
Dialogue: 0,0:03:34.73,0:03:37.11,Default,,0000,0000,0000,,sickness can also make you irritable,
Dialogue: 0,0:03:37.11,0:03:37.82,Default,,0000,0000,0000,,sad,
Dialogue: 0,0:03:37.82,0:03:39.23,Default,,0000,0000,0000,,and confused.
Dialogue: 0,0:03:39.23,0:03:41.30,Default,,0000,0000,0000,,That's because cytokines and prostaglandin\N
Dialogue: 0,0:03:41.30,0:03:44.38,Default,,0000,0000,0000,,can reach even higher structures \Nin your brain,
Dialogue: 0,0:03:44.38,0:03:46.96,Default,,0000,0000,0000,,disrupting the activity \Nof neurotransmitters,
Dialogue: 0,0:03:46.96,0:03:47.93,Default,,0000,0000,0000,,like glutamate,
Dialogue: 0,0:03:47.93,0:03:49.05,Default,,0000,0000,0000,,endorphins,
Dialogue: 0,0:03:49.05,0:03:50.24,Default,,0000,0000,0000,,serotonin,
Dialogue: 0,0:03:50.24,0:03:52.17,Default,,0000,0000,0000,,and dopamine.
Dialogue: 0,0:03:52.17,0:03:56.26,Default,,0000,0000,0000,,This affects areas like the limbic system,\Nwhich oversees emotions,
Dialogue: 0,0:03:56.26,0:04:00.70,Default,,0000,0000,0000,,and your cerebral cortex,\Nwhich is involved in reasoning.
Dialogue: 0,0:04:00.70,0:04:03.38,Default,,0000,0000,0000,,So it's actually the body's own\Nimmune response
Dialogue: 0,0:04:03.38,0:04:07.92,Default,,0000,0000,0000,,that causes much of the discomfort\Nyou feel everytime you get ill.
Dialogue: 0,0:04:07.92,0:04:10.91,Default,,0000,0000,0000,,Unfortunately, it doesn't always\Nwork perfectly.
Dialogue: 0,0:04:10.91,0:04:16.21,Default,,0000,0000,0000,,Most notably, millions of people\Nworldwide suffer from autoimmune diseases,
Dialogue: 0,0:04:16.21,0:04:21.20,Default,,0000,0000,0000,,in which the immune system treats\Nnormal bodily cues as threats,
Dialogue: 0,0:04:21.20,0:04:23.72,Default,,0000,0000,0000,,so the body attacks itself.
Dialogue: 0,0:04:23.72,0:04:25.69,Default,,0000,0000,0000,,But for the majority of the human race,
Dialogue: 0,0:04:25.69,0:04:29.48,Default,,0000,0000,0000,,millions of years of evolution\Nhave fine-tuned the immune system
Dialogue: 0,0:04:29.48,0:04:32.70,Default,,0000,0000,0000,,so that it works for, \Nrather than against us.
Dialogue: 0,0:04:32.70,0:04:35.22,Default,,0000,0000,0000,,The symptoms of our illnesses \Nare annoying,
Dialogue: 0,0:04:35.22,0:04:38.74,Default,,0000,0000,0000,,but collectively, \Nthey signify an ancient process
Dialogue: 0,0:04:38.74,0:04:43.13,Default,,0000,0000,0000,,that will continue barricading our bodies\Nagainst the outside world
Dialogue: 0,0:04:43.13,0:04:44.73,Default,,0000,0000,0000,,for centuries to come.