Science Questions

Where does phlegm come from?

Sun, 31st Oct 2010

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Question

Max Roberts asked:

I've been a bit sick lately, and I've been wondering where all the yellow phlegm I've been coughing up comes from.

I understand that there's a tube connecting my lungs with my mouth, but I don't see where so much phlegm can be held!

Answer

We posed this question to Dr Suzy Lishman...

Suzy -   There is a tube connecting the lungs to the mouth and thatís called the trachea.  Itís the Nose Blowone you can feel - if you just feel the front of your throat just under the Adamís apple, thatís the trachea.  Thatís lined by mucous membranes, the epithelial cells that produce mucus, which is a thick liquid that forms a phlegm. 

It has several functions; itís partly a lubricant, so it stops the airways from drying out when you breath dry air in and out, and it also helps get rid of bacteria and things that you really don't want to have down in your lungs.  They get stuck in this sticky mucus that lines the airways and then it can be coughed up, and it keep it away from the lungs. 

What happens when you get a cold is, in reaction to the extra irritation of your airways, these epithelial cells produce more and more mucus.  When you're fit and healthy, the mucus is normally clear and white, but if you get an infection, it can go yellow or even green, as you cough up all the bacteria and the dead cells that your lungs don't want.

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I get mine at phlegm are us. :D (Sorry, but I'm in a fairly jocular mood).  ;D Pmb, Tue, 22nd Oct 2013

When your lower airways (trachea, bronchi or lung) get inflamed they can be constantly producing phlegm, so when you cough up a certain amount, the new one will be produced. It's not that all the phlegm has to be in the airways at a certain moment.    healthresearch, Sat, 2nd Nov 2013

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