Name: 鳥類如何在蛋內獲取氧氣 (How Birds Get Oxygen Inside Their Eggs)
Uploaded: 2021-01-14T08:34:44.000Z
Duration: 3 min 11 s
Description: 【看影片學英語】數萬部 YouTube 影片，搭配英漢字典即點即查，輕鬆掌握單字發音與用法，長久累積看電影不必再看字幕。

It's a dramatic moment, that first breath

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.

An egg seems like a perfectly self-contained system.

The yolk and the white contain all the nutrients you need

As with a human baby, all this construction requires oxygen

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

When you magnify an egg's shell a thousand times

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

And these tiny holes let outside air filter in.

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

How does it get that oxygen into its bloodstream?

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

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

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.

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

That creates an empty space that gradually fills with air.

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

It punctures that air pocket and fills its lungs.

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

字幕列表影片播放

鳥類如何在蛋內獲取氧氣 (How Birds Get Oxygen Inside Their Eggs)

subscribe

delicate

develop

exact