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  • Our story is about a girl named Iris.

  • Iris is very sensitive.

  • So much that she is always in tears.

  • She cries when she's sad,

  • when she's happy,

  • and even tears up when things just get to her.

  • She has special lacrimal glands to make new tears

  • and special tubes, called lacrimal puncta,

  • to drain old ones away.

  • And she cries so much that she goes through

  • ten ounces of tears per day,

  • thirty gallons a year!

  • In fact, if you look closely,

  • you'll see that she's crying a little bit all the time.

  • The basal tears that Iris constantly produces

  • form a thin coating of three layers

  • that cover her and keep dirt and debris away.

  • Right next to Iris is the mucus layer,

  • which keeps the whole thing fastened to her.

  • On top of it is the aqueous layer,

  • which keeps Iris hydrated,

  • repels invasive bacteria,

  • and protects her skin, or cornea, from damage.

  • And, finally, there is the lipid layer,

  • an oily outer film that keeps the surface smooth

  • for Iris to see through,

  • and prevents the other layers from evaporating.

  • Normally, Iris goes about her day

  • without really noticing the basal tears

  • doing their thing.

  • That's kind of their whole point.

  • But one day, she meets a girl named Onion.

  • Iris is immediately smitten.

  • Onion looks gorgeous in her bright purple jacket,

  • and she smells terrific.

  • So, Iris invites Onion to her house for dinner,

  • but when she comes in and takes off her jacket,

  • something terrible happens.

  • You see, when Onion's jacket is removed,

  • a chemical reaction happens,

  • converting the sulfoxides that make her smell so great

  • into sulfenic acid,

  • which then becomes a nasty substance with a long name:

  • syn-Propanethial S-oxide.

  • The gas stings Iris,

  • and suddenenly, she can't help it,

  • she starts weeping uncontrollably.

  • These reflex tears are different from the basal tears that Iris is used to.

  • Because they're designed

  • to wash away harmful substances, or particles,

  • they're released in much larger amounts,

  • and their aqueous layer contains more antibodies

  • to stop any microorganisms that may be trying to get in, as well.

  • Both Iris and Onion are devastated.

  • They know they can't continue their relationship

  • if Iris is going to hurt and cry

  • every time Onion takes off her jacket.

  • So, they decide to break up.

  • As Onion walks out the door,

  • Iris stops crying.

  • And immediately starts again.

  • Only now, she's not crying reflex tears

  • but emotional tears.

  • When someone is either too sad or too happy,

  • it feels like a loss of control,

  • which can be dangerous.

  • So, emotional tears are sent in

  • to stabilize the mood as quickly as possible,

  • along with other physical reactions,

  • such as an increased heart rate

  • and slower breathing.

  • But scientists still aren't sure

  • exactly how or why the tears themselves are helpful.

  • They may be a social mechanism

  • to elicit sympathy or show submission.

  • But some studies have also found

  • that emotional tears contain higher levels

  • of stress hormones,

  • such as ACTH and enkephalin,

  • an endorphin and natural pain killer.

  • In this case, emotional tears are also directly calming Iris down,

  • as well as signaling her emotional state to others.

  • Sorry things didn't work out with Onion, Iris,

  • but don't worry.

  • As long as you have all three kinds of tears

  • working to keep you balanced and healthy,

  • it will get better.

  • You'll see.

Our story is about a girl named Iris.

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B2 TED-Ed iris onion basal jacket emotional

【TED-Ed】Why do we cry? The three types of tears - Alex Gendler

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    阿多賓 posted on 2014/03/12
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