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Common Cold

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Question: What happens during a Common cold inside the body? I want to know what actually happens inside the body during a common cold. Like is there a membrane that is affected? What is cough and why and how is it produced during a cold? Also why do people tend to catch cold when exposed to temperature extremes? Why do we feel weak during the cold? Do the glucose reserves in the muscles get depleted or what is it?

Answer: The common cold is a rhinovirus that effects the cells in the upper respiratory tract. Once it affects the cells, it triggers the sneeze and cough reflexes. This is good for the virus, because not only does it mutate rapidly (by the time you sneeze, you are most likely sneezing a different genome strain than effected you to begin with), but it promotes the spread of the virus to other hapless souls! Unlike other respiratory viruses that kick off the interferon system to fight infection, rhinoviruses interfere with interferon production. Why is this important? Because as the result of this evasion strategy, you get a runny nose and fever, caused by the innate immune system's inflammatory reaction to the virus, rather than the flu-like symptoms you would get if you had the flu. Because rhinoviruses are cytolytic (e.g. they kills the cells they infect), the innate system is on the lookout for excess cell death. Once it sees this happening, the innate system is so powerful, that it can eradicate the virus within a couple /few days. The cough is from a natural process in the body called the "mucosal escalator". There are 2-version, the 'up' and 'down' versions. In the 'down' version, which is relevant here, the mucus from the nasal cavity is moved 'down' to be swallowed. Once in the stomach, it's destroyed. This sounds good, right? Well...not so. When getting moved down, the temperature cools. What does rhinoviruses look for so they can replicate? Cool temperatures. Hence, the escalator actually helps the virus spread. Fortunately, the virus is also a weakling and the immune system can handle it at this point. As for a cold causing a cold, that's just a old wives tale. If that was the case, then everybody in colder climates would have colds virtually all the time, which, obviously, does not happen. Your immune response, the ability for the virus to remain labile in an environment and exposure to others who are transmitting a cold play more importance than the cold temperatures itself. You feel weak because the immune system is fighting a battle. Generally though a cold will make you feel more miserable rather than weak. Glucose reserves will not be really be affected because it's not causing a major systemic infection that limits appetite. You might feel lousy, but it won't stop you from eating pizza!

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