It starts with a tickle in your throat that becomes a cough. Your muscles begin to ache, you grow irritable, and you lose your appetite. It's official: you've got the flu. It's logical to assume that this miserable medley of symptoms is the result of the infection coursing through your body, but is that really the case? What's actually making you feel sick? What if your body itself was driving this vicious onslaught? You first get ill when a pathogen like the flu virus gets into your system, infecting and killing your cells. But this unwelcome intrusion has another effect: it alerts your body's immune system to your plight. As soon as it becomes aware of infection, your body leaps to your defense. Cells called macrophages charge in as the first line of attack, searching for and destroying the viruses and infected cells. Afterwards, the macrophages release protein molecules called cytokines whose job is to recruit and organize more virus-busting cells from your immune system. If this coordinated effort is strong enough, it'll wipe out the infection before you even notice it. But that's just your body setting the scene for some real action. In some cases, viruses spread further, even into the blood and vital organs. To avoid this sometimes dangerous fate, your immune system must launch a stronger attack, coordinating its activity with the brain. That's where those unpleasant symptoms come in, starting with the surging temperature, aches and pains, and sleepiness. So why do we experience this? When the immune system is under serious attack, it secretes more cytokines, which trigger two responses. First, the vagus nerve, which runs through the body into the brain, quickly transmits the information to the brain stem, passing near an important area of pain processing. Second, cytokines travel through the body to the hypothalamus, the part of the brain responsible for controlling temperature, thirst, hunger, and sleep, among other things. When it receives this message, the hypothalamus produces another molecule called prostaglandin E2, which gears it up for war. The hypothalamus sends signals that instruct your muscles to contract and causes a rise in body temperature. It also makes you sleepy, and you lose your appetite and thirst. But what's the point of all of these unpleasant symptoms? Well, we're not yet sure, but some theorize that they aid in recovery. The rise in temperature can slow bacteria and help your immune system destroy pathogens. Sleep lets your body channel more energy towards fighting infection. When you stop eating, your liver can take up much of the iron in your blood, and since iron is essential for bacterial survival, that effectively starves them. Your reduced thirst makes you mildly dehydrated, diminishing transmission through sneezes, coughs, vomit, or diarrhea. Though it's worth noting that if you don't drink enough water, that dehydration can become dangerous. Even the body's aches make you more sensitive, drawing attention to infected cuts that might be worsening, or even causing your condition. In addition to physical symptoms, sickness can also make you irritable, sad, and confused. That's because cytokines and prostaglandin can reach even higher structures in your brain, disrupting the activity of neurotransmitters, like glutamate, endorphins, serotonin, and dopamine. This affects areas like the limbic system, which oversees emotions, and your cerebral cortex, which is involved in reasoning. So it's actually the body's own immune response that causes much of the discomfort you feel every time you get ill. Unfortunately, it doesn't always work perfectly. Most notably, millions of people worldwide suffer from autoimmune diseases, in which the immune system treats normal bodily cues as threats, so the body attacks itself. But for the majority of the human race, millions of years of evolution have fine-tuned the immune system so that it works for, rather than against us. The symptoms of our illnesses are annoying, but collectively, they signify an ancient process that will continue barricading our bodies against the outside world for centuries to come.
Počinje sa grebanjem u vratu pre nego što preraste u kašalj. Počinju da vas bole mišići, postajete razdražljivi, a zatim gubite apetit. Zvanično ste dobili grip. Logično je pretpostaviti da je ovaj mučni skup simptoma posledica infekcije koja vam prolazi kroz telo, ali da li je stvarno tako? Zbog čega se zapravo osećate loše? Šta ako samo vaše telo podstiče taj grozni napad? Najpre se razbolite kada patogen kao što je virus gripa uđe u vaš sistem, zarazi i ubija vaše ćelije. Međutim, ovaj nepoželjni upad ima još jedno dejstvo - on upozorava imuni sistem vašeg tela na vaše loše stanje. Čim postane svesno infekcije, vaše telo priskače u vašu odbranu. Ćelije zvani makrofagi nastupaju kao prva linija napada, tražeći i uništavajući viruse i zaražene ćelije. Nakon toga, makrofagi otpuštaju molekule proteina zvane citokini čiji je posao regrutovanje i organizovanje dodatnih ćelija za uništavanje virusa iz vašeg imunog sistema. Ako je ovo udruženo nastojanje dovoljno jako, uništiće infekciju pre nego što i primetite. Međutim, to samo vaše telo podešava scenu za pravu akciju. U nekim slučajevima, virusi nastave da se šire, čak i u krv i vitalne organe. Da bi izbegao ovu ponekad opasnu sudbinu, vaš imuni sistem mora da pokrene jači napad, usklađujući svoju aktivnost sa mozgom. Otuda proizilaze ti neprijatni simptomi, počevši od nagle temperature, bolova i pospanosti. Zašto prolazimo kroz ovo? Kada je imuni sistem pod ozbiljnim napadom, on luči više citokina, što izaziva dve reakcije. Prvo, živac lutalac, koji prolazi kroz celo telo do mozga, brzo prenosi informacije do moždanog stabla, prolazeći pored važne oblasti za obradu bola. Drugo, citokini putuju kroz telo do hipotalamusa, dela mozga koji je odgovoran za kontrolu temperature, žeđi, gladi i spavanja, između ostalog. Kada primi ovu poruku, hipotalamus proizvodi drugi molekul zvani prostaglandin E2, koji se priprema za rat. Hipotalamus šalje signale koji nalažu vašim mišićima da se zgrče i dovodi do porasta telesne temperature. Takođe vas čini pospanim, a gubite i apetit i osećaj žeđi. Koja je svrha svih tih neprijatnih simptoma? Pa, nismo još sigurni, ali neki imaju teoriju da oni pomažu oporavku. Porast temperature može da uspori bakterije i da pomogne vašem imunom sistemu da uništi patogene. Spavanje omogućava da vaše telo usmeri više energije na borbu protiv infekcije. Kada prestanete da jedete, vaša jetra može da preuzme veći deo gvožđa u krvi, a budući da je gvožđe suštinski važno za opstanak bakterija, to ih delotvorno izgladnjuje. Smanjen osećaj žeđi vas blago dehidrira, čime se umanjuje prenošenje putem kijanja, kašlja, povraćanja ili dijareje. Doduše, treba napomenuti da, ako ne pijete dovoljno vode, ta dehidratacija može postati opasna. Čak i bolovi u telu čine vas osetljivijim, privlačeći pažnju na inficirane posekotine koje se mogu pogoršavati, ili čak izazvati vaše stanje. Pored fizičkih simptoma, zbog bolesti možete biti razdražljivi, tužni i zbunjeni. To je zato što citokini i prostaglandin mogu da prodru čak i do viših struktura u mozgu, ometajući aktivnost neurotransmitera kao što su glutamat, endorfini, serotonin i dopamin. To pogađa oblasti poput limbičkog sistema, koji nadgleda emocije, i vašeg cerebralnog korteksa, koji je u vezi sa rasuđivanjem. Dakle, zapravo je reakcija imunog sistema samog tela ono što izaziva veći deo neugodnosti koju osećate kad god se razbolite. Nažalost, to ne funkcioniše uvek savršeno. Pre svega, milioni ljudi širom sveta pate od autoimunih oboljenja, kod kojih imuni sistem tretira normalne telesne signale kao pretnje, tako da telo napada samo sebe. Međutim, kod većine ljudskog roda, milioni godina evolucije su podesili imuni sistem tako da radi za nas, umesto protiv nas. Simptomi naših bolesti su iritirajući, ali zajedno označavaju prastari proces koji će nastaviti da služi kao prepreka između našeg tela i spoljašnjeg sveta u predstojećim vekovima.