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  • Look inside this incubator.

  • These eggs were laid 21 days ago

  • and this one is just about to hatch.

  • If you listen you can hear the chick

  • pecking at the inside of its shell.

  • Soon it will break through

  • and take its first breath of fresh air.

  • It's a dramatic moment, that first breath

  • - one shared by so many creatures -

  • including ... us.

  • But hold on, think about this: When you were in the womb

  • you got oxygen from your mother through your umbilical cord.

  • But for the last 21 days this chick has been cut off from its mother - sealed inside an egg.

  • So how does it get oxygen?

  • An egg seems like a perfectly self-contained system.

  • The yolk and the white contain all the nutrients you need

  • to build a baby chick.

  • As with a human baby, all this construction requires oxygen

  • and that's the one thing that isn't stored inside the egg.

  • So where does it come from?

  • Well take a look at this.

  • When you magnify an egg's shell a thousand times

  • you can see the calcium carbonate crystals that make up the shell

  • and here and there -- tiny holes.

  • One thousandth of an inch across.

  • And these tiny holes let outside air filter in.

  • So oxygen can pass through the shell but the chick growing inside

  • doesn't have working lungs yet.

  • How does it get that oxygen into its bloodstream?

  • Well, a few days after an egg is laid

  • something amazing happens.

  • When you hold a fertilized egg up in front of a bright light, you can see it:

  • a delicate network of blood vessels that grows out of the embryo's abdomen

  • and presses up against a membrane just inside the shell.

  • Oxygen from the air comes in through the tiny holes in the shell

  • then diffuses into the embryo's blood.

  • And the growing chick gets rid of carbon dioxide at the same time.

  • It all looks remarkably similar to your early days in the womb

  • There was a yolk sac, at least at first,

  • and a network of blood vessels growing out from

  • the place where your belly button now is.

  • But instead of pressing up against the edge of a shell

  • your blood vessels reached the wall of the womb

  • where they joined with an outer membrane to form the placenta.

  • In the placenta, oxygen from your mother diffused into your bloodstream.

  • It really is an exact mirror of what's going on in the eggs of birds and reptiles.

  • While all this is happening, lungs are developing.

  • We humans don't fill those lungs with air until after we're born.

  • But chicks get a head start.

  • That's because the whole time oxygen is coming in through the shell.

  • Moisture is slowly evaporating out.

  • That creates an empty space that gradually fills with air.

  • A day or so before the chick is ready to hatch,

  • it starts to move.

  • It punctures that air pocket and fills its lungs.

  • It then has just enough oxygen to battle out of the egg

  • and take its first breath of fresh air.

  • This is Skunk Bear, NPR's science show

  • Please subscribe to our channel

  • and check out our other videos!

Look inside this incubator.

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B2 中上級

鳥が卵の中に酸素を取り込む方法 (How Birds Get Oxygen Inside Their Eggs)

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    Anbe2623 に公開 2021 年 01 月 14 日
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