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If you've got a cold,
mucus is hard to miss.
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But what is it, and what does it do
besides making your miserable?
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Your body produces more than a liter
of mucus every day,
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and all the wet surfaces of your body
that are not covered by skin,
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like your eyes,
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nose,
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mouth,
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lungs,
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and stomach get a liberal coating.
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That's why they're known
as mucus membranes.
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Mucus plays lots of roles
in your body.
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It keeps delicate tissues
from drying out and cracking,
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which would expose them to infection.
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It lubricates your eyes so you can blink.
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It protects your stomach lining
from acid.
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It neutralizes threats by removing
or trapping substances
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that could make you sick.
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And finally, it houses and keeps your
body's trillions of bacterial inhabitants,
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your microbiota, under control.
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Mucus contains lots
of different compounds,
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including proteins, fats, and salts.
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But a key component of mucus versatility
is a set of proteins called mucins.
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Mucins are the primary
large molecules in mucus
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and are essential
for giving mucus its slippery feel.
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They belong to a class of proteins
called glycoproteins
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which are built out of both amino acids
and sugars.
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In mucin, long chains of sugar
are attached to specific amino acids
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in the protein backbone.
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The hydrophilic sugar chains help mucin
dissolve in your body's watery fluids.
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Mucus, which is up to 90% water,
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stays hydrated thanks
to these sugar chains.
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Some of these mucins can interact
with other mucin molecules
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to create a complex network
that establishes a barrier
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against pathogens and other invaders.
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That's why mucus is the body's first line
of defense against foreign objects,
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like bacteria and dust.
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It's continuously produced to clear them
from the resperatory tract,
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like a slimy conveyor belt.
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This keeps bacteria from getting
a solid purchase on delicate lung tissue,
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or making it to the blood stream,
where they could cause a major infection.
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Many of those harmful bacteria
also cause diseases
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when they cluster into slimy growths
called biofilms.
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But mucus contains mucins,
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antimicrobial peptides,
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antibodies,
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and even bacteria-hungry viruses
called bacteriophages
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that all work together to prevent
biofilms from forming.
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If microbes do become harmful
and you get sick,
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the body ramps up mucus production
to try to quickly flush out the offenders,
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and the immune system floods your mucus
with extra white blood cells.
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In fact, the greenish mucus often
associated with infections
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gets its color from an enzyme
produced by those white blood cells.
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This multi-pronged approach
to bacterial management
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is one of the main reasons
why we're not sick all the time.
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Even though mucus protects against
the infectious bacteria,
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the vast majority of your body's bacterial
tenants are not harmful,
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and many are actually beneficial.
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That's particularly true
when they live in mucus,
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where they can perform
important functions,
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like synthesizing vitamins,
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suppressing harmful inflamation,
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and controlling the growth
of more harmful species.
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So even though you probably associate
mucus with being ill,
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it's really helping you stay healthy.
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Sure, it might seem gross,
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but can you think of any other substance
that can lubricate,
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keep your body clean,
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fight infection,
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and domesticate a teaming
bacterial population?
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Nope, just mucus.