How does an ostrich egg breathe?

[snorkack]

Birds are warm blooded, with intense metabolism.

How does an ostrich egg/chick breathe?

A mammal young of similar size has placenta. Air is actively breathed into mother´s lungs, then the blood is circulated to womb, where it is across a thin membrane from the young mammal´s placenta and circulating blood there.

Whereas an ostrich chick may have blood circulation and placenta inside the egg... but then there is a thick eggshell.
How does adequate amount of air to meet the intense metabolism of a big ostrich chick get through the thick eggshell by mere diffusion? Surely the skin of a a human baby is bigger, thinner and more permeable to air than the shell of an ostrich egg... if ostrich egg does not need mouth to inhale into lungs then what does a child need throat for?

 

[jim mcnamara]

Could I ask you to stop making assumptions, please.
A fetus does not breathe air, which your post seems to indicate. The placenta provides oxygenated blood. Human babies breathe air after they come out of Mom.
Not before.

Chicks in an egg are the same. No breathing of consequence up until just before they crack open the egg.

First off, does the egg allow chicks to mature and to hatch? Yes. So how does it work - which is what you are asking. Early embryos in an egg are not homeothermic, so their energy and O₂ requirements are reduced. A lot. In fact, altricial (or helpless at birth ) birds require mother's warmth well after hatching, precocial birds require much less brooding, except in bad weather. Mom bird and/or Dad bird and sometimes the sun provide the energy for maintaining body warmth of unhatched chicks. Result: few calories to be burned using oxygen to maintain body temperature.

Okay so your assumptions about O₂ got a tune up.

Next, the answer: diffusion of oxygen in /CO₂ out. Through the shell. Here is a discussion about egg shells which has lots of points, I think. It compares chicken eggs with ostrich, and has good diagrams.
https://pdfs.semanticscholar.org/3ea5/4a1ac775c99c27986ccb10c4952f37eb77a9.pdf

 

[Dale]

Birds are warm blooded, with intense metabolism.

How does an ostrich egg/chick breathe?

A bird egg is not warm blooded. That is why it must be incubated.

 

[BillTre]

If you have them available to you, you could get hold of some fertilized chicken eggs (or any other bird, but chicken development has a well determined sequence to direct your viewing and eggs are often available).

If you crack a few eggs open after they have been developing for a couple of weeks or so, you will see that in inside surface of the egg shell has a lot of blood vessels.

The blood in them is driven by the beating of the embryo's heart and carries oxygen in the blood from the surface of the egg (under the egg shell) back to the developing embryos. The shell allows gas exchange through it and the layer of blood vessels and acts somewhat like a lung or gill.
Prior to the development of the blood system at the egg's surface, gas exchange would be driven by diffusion to the developing embryo (which would have even smaller oxygen needs early in development. Also the embryo is not that far from the surface of the egg, which would make it easier to the needed gas exchange to occur.

Like others have said, the metabolic need for oxygen in embryos is not so great compared to a active, self-heating bird flying around.

There are other cases of organisms not having normal lungs or gills and still getting sufficient gas (oxygen and carbon dioxide) exchange, like lungless salamanders which use their moist skin surface for gas exchange.
A baby's skin can't do this, too thick for much gas to pass through, not enough vasculature (blood vessels) to support enough gas exchange to the interior of the organism.