The Lungs Travelator -cilia and mucous

epithelium showing cilia and mucous glandsFrom the nose all the way down through the conducting portion of the lungs ( the first 16 of the 23 divisions) there is a continous level of activity protecting your body from unwanted inhaled particles. You have a few types of mucous cells scattered along the respiratory system, the goblet cells and submucosal glands. Healthy lungs will produce about 100ml every day. Cilia waft to keep it moving, so it is moved to our throat from our nose or up from the lungs and when healthy we swallow it without even noticing.
Mucous is Great Stuff. And if you can refrain from going ‘Gross – that’s too much information already’, just read on and I hope I can inspire you to have a healthy respect for it.  You know how dry your mouth gets if you breathe through it all day, so imagine how dry and open to infection all your airways would be without constant moisturising.


So its not watery like saliva, it has proteins in it which make it a bit gooey to trap dust or bacteria or smoke chemicals, a bit like fly paper holds onto unsuspecting insects. It has salts to equalise it to our body fluids, and even some white blood cells and enzymes to engulf or destroy any organisms in the air.

Colour is a touchy subject for some and this bit shouldn’t be read out at the meal table…

Mucous is normally clear, but if it turns yellow and then green it is a sign your body is fighting off some bugs. The green colour comes from a green enzyme produced by a certain type of white blood cell, the neutrophils, which are always the first on the scene, and they are short lived so it just shows that a lot of them were present and gave up their lives to work on your behalf.
If the mucous is occasioanlly streaked brown, it means that a normal response of your lungs to infection, an inflammatory process, was going on in your lungs, and some superficial blood vessels got red and swollen and may have broken to disharge some blood, a normal part of the process.
BUT if it happens a lot or if you have red blood in your sputum it is important to go and see a doctor soon.
If you drink a lot of dairy food, you may find your mucous may also look milky and white.

Cilia are tiny motors

These are the travelators that keep the mucous moving.  They are 1000 times smaller than a human hair so although you will know that it takes powerful microscopes to let you see an individual cell, there are hundreds of these tiny work horses on the surface of each cell.  Biologist Michael McDarby has a great image for you to click on to show cilia in motion. They complete about 15 of these cycles a minute, so move mucous at about 10 mm a minute up toward the throat. Michael J. Welsh, an investigator at teh Howard Hughes Medical Institute says that “Cilia are almost like a little antenna” He found that cilia could sense bitter material in the airways and beat 25% faster than normal to expel it. (source)

The cilia are themselves bathed with a liquid called perciliary fluid, so only the cilia tips are in contact with the mucous. There needs to be a balance between the amount of thin Perciliary fluid and mucous for effective clearance.
perciliary lining   In a disease called cystic fibrosis where there is a reduced volume of perciliary fluid, the cilia are unable to function effectively and mucous collects. The perciliary fluid is also reduced when you are dehydrated.



2nd cross section of cilia

AND inside each tiny tiny cilia there are nine sets of double microtubules around the diameter and one set in the middle that work like muscles to move the cilia in the wave motion that McDarby drew.

So here we are again, blown away by the fact in my last article that we swallow 100 million macrophages a day from the alveoli, and now trillions of these work horses doing a thankless job in our lungs!

We are very spoilt.