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  • You know how it feelsthat crushing headache, a building pressure in your face, and thick mucus dripping down the back of your throat.

  • Sinusitis, or sinus infections, are incredibly common and no fun whatsoever.

  • Anywhere from thirty to thirty five million sinus infection diagnoses are made every year in the US.

  • They're one of those sicknesses that usually go away on their own, but they're a nuisance nonetheless.

  • And in fact, our tendency to get sinus infections might actually be a quirk of human evolution.

  • There's dust, pollution, and pathogens like viruses and bacteria in every breath we take, and one tool that our body uses to keep us healthy is our nasal cavities.

  • Within the fleshy nose itself, hair and mucus catch big dust particles, which is a good first line of defense for keeping our lungs clean.

  • From there, our breath enters a series of air-filled chambers behind the facial bones called the paranasal sinuses.

  • Paranasal for around the nose, sinus for empty space.

  • Their first job is to warm and humidify air, making it easier to breathe when it gets down to the lungs.

  • The next line of defense is mucusand it's totally normal.

  • We're all secreting at least a little mucus all the time.

  • Each of our sinuses are lined with cells that can make more or less mucus depending on the situation.

  • They're also coated in cells that have little hair-like structures called cilia.

  • These things wiggle back and forth to keep this mucus moving down collection ducts in each of our sinuses where they drain into the nasal cavity, then into the throat.

  • This becomes more complicated when you get a sinus infection.

  • Which is exactly what it sounds like: infection from pathogens or allergens that stick around in your sinuses, like from a cold or flu, which then causes inflammation of these mucus membranes.

  • Most of the time, these pipes and chambers flow freely, and we can take big clear breaths.

  • But when sinuses have to deal with germs, it results in clogged up noses and difficulty breathing.

  • Viruses cause the majority of sinus infections, but bacteria can trigger them as well.

  • When you do get a sinus infection, that wet mucus gets thicker and more viscous, which causes the typical symptoms: congestion, headache, and difficulty breathing.

  • And those symptoms might be made worse by the plumbing of our sinuses.

  • Each sinus has a mucus collection duct, or what are called ostia, to shuttle its discarded mucous to the nose and throat.

  • It's basically plumbing for snot.

  • Well for most of our sinuses like the frontal sinuses behind the forehead or the sphenoid sinuses a few centimeters behind our eyes, the collection duct is towards the bottom of the sinus.

  • The ethmoid sinus has a bunch of tiny cavities that it drains out of, but it still drains downward.

  • The big exception then is the maxillary sinuses: the ones behind our maxillas, or upper lip and cheeks area.

  • These are our biggest sinuses, at about 15 milliliters, and the ones that most often get infected.

  • And for most humans, we have one collection duct towards the top innermost wall of the maxillary sinus.

  • Having the collection duct at the top of sinus might keep us from draining all that collected snot more efficiently.

  • Which, in turn, might predispose humans to sinus infections.

  • On one hand, if you have a sinus infection, your cilia have to wick a bunch of thick, viscous mucus towards the collection duct against gravity,

  • and that mechanism tends not to work as well when we have an infection.

  • So we end up with more and more bacteria which creates infinite snot and makes symptoms worse.

  • On the other hand, that duct might act like an overflow drain.

  • That's why it sometimes helps to lie down or bend forward when you have a sinus infection: it helps drain mucus towards the ducts.

  • Obviously that doesn't remove the infection, but it might help for a little bit.

  • Ultimately, the location of the maxillary ostia is a consequence of evolving from ancestors that walked around on four legs.

  • Asking whether our bodies would work better if it had different anatomy is a hard question to test scientifically, so researchers might compare our anatomy to a different animal's.

  • Like in the past decade, scientists published a paper where they filled human sinuses and goat sinuses with a saline solution and measured how quickly they drained.

  • In an upright position, the human sinuses didn't drain that well, but when they were tilted forward, they drained as quickly as the goats' did.

  • On a practical level, different scientists also showed that moving into the quadrupedal head position, essentially just leaning forward, does relieve sinusitis symptoms.

  • That makes them think that the location of the sinus ostia was appropriate for our four legged ancestors, but not for modern humans on two legs.

  • But, it's also worth remembering that everyone has slightly different nasal anatomy which might predispose some people to sinus infections more than others.

  • While our sinuses might be designed less than ideally, having a big brain was more important, so we're left with the nasty, snotty consequences of evolution.

  • While we can't go back in time to say if this was a good or bad design, our sinuses are something that make us human.

  • Thanks for watching this episode of Seeker Human.

  • We're so excited to get more episodes of Human to you just a little bit, so make sure you're subscribed on YouTube and following us on social media

You know how it feelsthat crushing headache, a building pressure in your face, and thick mucus dripping down the back of your throat.

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Why Do Humans Get So Many Sinus Infections?

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    林宜悉 posted on 2020/12/26
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