Apple #361: Mucus

Fair warning: this first Daily Apple of this new year will be quite high on the Ew scale. I had a cold (maybe also mixed in with a bit of flu) that lasted a couple of weeks, and I'm still using a lot of tissues every day. So I have many questions about mucus. It is a very strange substance. And our bodies manufacture it. Happily and willingly. All the time.

So get ready to say "Ew!" at least once, if not several times, as you read this.

First of all, what is it?

• Dorland's Medical Dictionary defines mucus as follows: "the free slime of the mucus membrane, composed of [mucin] the secretion of its glands, various salts, desquamated cells, and leukocytes."

• Translation: mucus is made of:

1. water
   
2. salts
3. mucin, which is a nitrogen-rich, gooey protein
4. dead cells that have been sloughed off
5. white blood cells
   

• It lines not just your nose, but also your throat, lungs, ears, intestinal tract, urinary tract, and if you're female, your vagina.

• So, phlegm, sputum, boogers, even ear wax (though it's a specialized type) -- it's all mucus.

All these places are lined with mucus. As are many other parts of the body.
(Chart from Live Wire Learning)

• As my copy of Gray's Anatomy puts it, you've got mucus membranes any place where an internal organ might come in contact with anything external.

• You've even got mucus membranes under your tongue.
  

What is its purpose?

• Primarily, mucus is a protective substance.
  

• Its gooiness helps trap any unwanted particles. It acts like a glue which snags any dust or tiny nasties floating around in the air. Those things get trapped in your mucus, but that means they don't make it all the way into your lungs or your intestine where they'd really cause a problem. If they're in the mucus in your nose, you can just sneeze or cough the stuff out of you, no big deal.

• The white blood cells in the mucus are another key part of mucus' ability to protect you from the nasties. They help to fight against bacteria and viruses and other nasties that can make you sick, right on the spot.

White blood cells. Their hairy-looking shape allows the cells to trap and engulf the nasties.
(Photo from the University of Iowa)

• In addition, most mucus membranes sit on top of a bunch of lymphatic vessels -- vessels which deliver substances that can fight against bacteria and cancer cells. So the mucus traps and keeps the nasties in place, and whatever the white blood cells can't conquer, the lymph vessels will try to defeat.

• Finally, most of the places lined with mucus are also lined with cilia, tiny little hairs. The tiny little hairs keep things moving out. They move along the mucus, and they move along anything else that's trapped in there.

Cilia in the lungs.
(Photo from Wikipedia)
Biologist Michael McDarby has a really cool diagram showing cilia in motion.

• The moistness of mucus also helps to humidify the air you breathe in. Have you ever been in really cold weather, so cold the inside of your nose feels like it freezes? If you have, then you know what it would feel like to inhale without the benefit of mucus: the air feels really cold and also piercing because it's way too dry.
  

• The moistness is also useful in other passages. In the intestine, it helps food move along more easily. In the vagina and cervix, in addition to helping prevent infection, the mucus also tries get things moving farther in -- specifically, the spermatozoa toward the egg.

Mucus: aiding and abetting the cause of life, even here.
(Photo from Wikipedia)


Other stuff to know

• The word "mucus" comes from the Greek word mussesthai which means, "to blow the nose."

• Most of the time, mucus is clear.

• When it turns yellow and then green, that means it's fighting off some sort of nastiness.
  

• The yellow and green colors don't come from the nasty thing, but from the white blood cells which are hard at work.

• If you drink a lot of dairy, your mucus may also turn white, or milky.

• Medical professionals debate a lot about whether certain colors are associated with which type of white blood cells, or whether you can tell the difference between an allergic reaction and the presence of viruses, etc. Because they're not really sure what the color indicates, they just tell people that you can't diagnose anything based on mucus color alone.
  

• Our bodies produce one to two quarts of the stuff per day. Normally, we don't pay any attention and swallow whatever mucus drains from our nose into the throat.

• When it makes more than two quarts, that's when we notice it.

Motor oil is sold in one-quart containers. When your nose is making lots of mucus, it's making about the same amount as what you'd get in two of these quart bottles. That's a lot of mucus.
(Photo from Alphaworkx)


This is 1-3/4 quart, or about the upper limit of what your body produces in mucus, per day.
(Photo from Amazon, sourced from Road Food.com)

• If you've got a cold or some sort of infection, your body will produce extra mucus. Because it's staying on site, so to speak, you'll feel it clogging up your sinuses and in your lungs.

• Drinking lots of liquids can help moisturize everything and keep things moving. Eating warm soup or drinking warm tea or taking steamy baths or showers can help loosen the goo, too.

This has been me, more or less, for the past three weeks: tissues and herbal tea, ad infinitum.
(Photo from Barnard College)


In a lot of horror movies, you know the alien or the monster has been there by the mysterious, mucus-like, ectoplasmic goo they leave behind (think of the library scene in Ghostbusters, and all the goo that always drips off the alien in the Alien movies).

But that's actually an injustice to mucus. I'm very pleased to realize that mucus is on our side, fighting the good fight. Who knew, mucus is one of the good guys?

You might also be interested in my entry about sneezing.

Sources
OneLook, mucus and mucin
Cari Nierenberg, "You Think It's Mucus, but It's Not," ABC News Medical Unit, December 10, 2008
Jessica Saras, About Mucus, eHow
SinusWars, What is mucus?
Steven B. Harris, M.D., Mucus color Usenet thread
My copy of the OED
My copy of Gray's Anatomy