How do fetuses breathe in the womb?

[sevensages]

TL;DR Summary

How do fetuses breathe in the womb?

When human babies are first born, they need to breathe immediately at birth. I don't think think that the umbilical cord carries air to the human fetus to provide oxygen. I don't think human fetuses can get oxygen from liquid (blood) like a fish does because human fetuses don't have gills.

How do 8-month old human fetuses breathe in the womb?

If the human fetuses don't breathe in the womb, how do they get their oxygen?

 

[BillTre]

I don't think human fetuses can get oxygen from liquid (blood) like a fish does because human fetuses don't have gills.

This is wrong.
The mother breathes in air, hemoglobin in the blood binds the oxygen from the air. Some of that blood goes to the mother's side of the placenta (the placenta is a specialized exchange structure) where it is released and then picked up by hemoglobin in the baby's blood and distributed throughout the baby's body as needed.
The baby's hemoglobin has binding properties different from the mothers (different gene's are used to make the different hemoglobin proteins), such that the oxygen is efficiently transferred to the baby's circulation.

Also all vertebrate embryos have at least vestigial gills. As embryonic structures they later become things like lower jaws and a variety of throat structures and organs. In many cases they don't work as gills.

There are some weird animals that have neither lungs nor gills for getting oxygen. Some small species of salamanders just breath (do gas exchange) through their skin. Some hibernating turtles (in a low metabolic state) such water into their butts at the bottom of a pool and do gas exchange across their intestinal lining. Very small embryonic fish don't have functioning gills early in their lives. They also gas exchange across their skin. The combination of being small and not having a very active metabolism makes it possible for these less efficient methods to work for them.

 

[Drakkith]

The placenta, a temporary fetal organ, grows along the inside of the mother's uterus and exchanges gas (and other things) between the fetal and mother circulatory systems.

See here: https://en.wikipedia.org/wiki/Placenta

 

[sophiecentaur]

The baby's hemoglobin has binding properties different from the mothers

This is an incredibly clever system. Haemoglobin is a very smart molecule which binds to Oxygen very loosely. So much so that it picks up O2 molecules in the lung but can release those molecules very easily at the interface in the placenta (and everywhere else in the body.. The foetal Haemoglobin is just a bit 'stickier' then the mother's so it picks up the O2 in the placenta. A very small concentration gradient is all that's needed.

Interesting fact: New-born babies often show signs of jaundice because their liver needs to flush out the old red cells with new ones with the regular haemoglobin. It's not necessarily a sign of malfunction.

Also, there's a brilliant change in plumbing that takes place at birth. The blood is eventually directed away from the umbilical cord and through the lungs so a baby needn't breathe immediately after birth. There's less of a panic than you'd think when the little dear keeps you waiting for its first breath / cry.

 

[BillTre]

This is an incredibly clever system.

Some biologists like to think of this fine tuning of function to the animal's environmental needs as a slow long term learning that is mediated by evolution and imposed on the living things structure and function. They will often say that the organism is the result of it evolutionary history of these engineering modifications of its biology. Its an interaction among the organism's population, and what it can do with its environment, and what it can mutate to (its adjacent possible in the kinds of things it can mutate to.

Interesting fact: New-born babies often show signs of jaundice because their liver needs to flush out the old red cells with new ones with the regular haemoglobin. It's not necessarily a sign of malfunction.

My son had this. We had him in an illuminated vest like thing for a few hours/day. The light broke down the bilirubin which is the problematic chemical.

Also, there's a brilliant change in plumbing that takes place at birth. The blood is eventually directed away from the umbilical cord and through the lungs so a baby needn't breathe immediately after birth.

This is triggered by a thyroxine (hormone from the thyroid gland) spike prior to birth.
Thyroxine also triggers metamorphosis in things like amphibians. Some think the mammalian time around birth is the equivalent to metamorphosis in amphibians.

 

[gmax137]

Nothing to add, just want to say this is a fascinating thread!

Thyroxine also triggers metamorphosis in things like amphibians. Some think the mammalian time around birth is the equivalent to metamorphosis in amphibians.

Wow.

 

[BillTre]

Nothing to add, just want to say this is a fascinating thread!


Wow.

Biological evolution is a long and winding road.

 

[Drakkith]

More 'wow' factor for everyone:

One of the primary proteins necessary for the development of the placenta (Syncytin-1) is believed to be of viral origin. That is, millions of years ago a retrovirus infected a germ cell in one of our ancestors. This provirus (viral genome integrated into the DNA of a cell) was then passed to the animal's offspring and then their offspring and so forth. Over time the DNA of the provirus accumulated errors, inactivating most of it, but leaving the gene for one of its proteins intact. This protein is crucial for the attachment of the placenta to the uterus.

Mammals exist today as they are because we coopted the DNA of a retrovirus. And this is not the only time this has happened!

 

[sophiecentaur]

And this is not the only time this has happened!

That sort of mechanism could explain the apparent phenomenon of 'Punctuated Equilibrium' which the proponents of intelligent design explain in terms of a need for some sort of devine intervention. Yet another limited view (due to our very finite intellectual capacity) which leads to a desire for some sort of god figure rather than acceptance of everything being well beyond our comprehension. Frankly, I don't mind accepting my limitations.
(Frequently pointed out by other contributors to PF. )

 

[jim mcnamara]

really good thread...

 

[sophiecentaur]

@Drakkith I liked your 'like' . Meant in the nicest possible way, I'm sure.

 

[ShadowKraz]

Mammals exist today as they are because we coopted the DNA of a retrovirus. And this is not the only time this has happened!

Not just mammals either. I wonder how much of evolution has been due to co-opting such as this and how much is from mutation of existing genes.

 

[sophiecentaur]

Not just mammals either. I wonder how much of evolution has been due to co-opting such as this and how much is from mutation of existing genes.

Every Genetic Engineer should have a warning about this over the bathroom mirror. It's quite scary actually and enthusiasm could lead to serious problems.

 

[ShadowKraz]

Every Genetic Engineer should have a warning about this over the bathroom mirror. It's quite scary actually and enthusiasm could lead to serious problems.

The only problem I have with genetic engineering is that our species doesn't take the time to think things all the way through, but instead stops thinking when we have an answer we like (for whatever reason). Granted, we don't usually have all the information that might make our thinking better, but that alone should give us pause to stop and either re-think or find out. Yes, the basis of science is doing that but we can all bring up examples where scientists were simply quite human and didn't re-think or find out more.

 

[BillTre]

You guys are really underestimating the current regulations and safeguards currently existing for recombinant DNA procedures.

In addition, while complaining about that you completely overlook the virtually unregulated and much more poorly defined "natural" breeding operations involved in things like making crosses between two different crop species. In molecular manipulations single specific changes are usually made and have to be tested in a number of ways before they can be released for widespread use. Genetic crosses are mostly completely unregulated and involve hundreds or thousands of genetic changes throughout the genome.

 

[ShadowKraz]

You guys are really underestimating the current regulations and safeguards currently existing for recombinant DNA procedures.

In addition, while complaining about that you completely overlook the virtually unregulated and much more poorly defined "natural" breeding ...

No, I'm not, I'm saying we simply do not have the data to know for certain that we aren't going to make a major mistake, maybe even quite a few. And, no, I haven't overlooked 'natural breeding' programs. They are also a big risk for mistake due to insufficient knowledge. I didn't mention them as they were not the subject of the comments so far.
I'm very much in favor of genetic research and experimentation for the very fact that we don't really know what risks we are taking yet. My issue is with implementation; money/profit is generally the deciding factor, not the possible risks involved. This reflects back to my earlier statement about our species habit of stopping thinking when we have an answer we like.

 

[berkeman]

I'm very much in favor of genetic research and experimentation for the very fact that we don't really know what risks we are taking yet.

Sorry, I'm having trouble parsing this sentence. Is there a word missing perhaps?

 

[ShadowKraz]

Sorry, I'm having trouble parsing this sentence. Is there a word missing perhaps?

No. What do you think it means?

 

[berkeman]

No. What do you think it means?

I'm confused that you say you are "in favor" of genetic research and experimentation because it's dangerous and we don't understand what we are doing. That seems like a strange mindset to me.

 

[sophiecentaur]

“BUT for the very fact”?

I have to agree. Scientists and medics are far too optimistic about their ideas and plans. Regulations about experimentation are influenced by financial interests - big pharma , oil. etc.
Genetic research is such an attractive prospect. We need protecting from ourselves. ‘Natural’ breeding if enough of a danger as it is.

 

[berkeman]

“BUT for the very fact”?

My that's a big BUT!

 

[BillTre]

No, I'm not, I'm saying we simply do not have the data to know for certain that we aren't going to make a major mistake, maybe even quite a few.

One can say this about almost anything.

And, no, I haven't overlooked 'natural breeding' programs. They are also a big risk for mistake due to insufficient knowledge. I didn't mention them as they were not the subject of the comments so far.

It seems an out of proportion reaction to genetic engineering then when all the other stuff that is going on.

My issue is with implementation; money/profit is generally the deciding factor, not the possible risks involved. This reflects back to my earlier statement about our species habit of stopping thinking when we have an answer we like.

This makes it sound like your hammer is this argument which you use on all those things you don't understand well, like the recent history of genetics perhaps.

 

[Tom.G]

The only problem I have with genetic engineering is that our species doesn't take the time to think things all the way through, but instead stops thinking when we have an answer we like (for whatever reason).

Isn't that the way evolution works? If it survives it must be "good" in some aspect.

Reference amoeba to fish, dinosaurs to Humming birds, apes to homosapiens.

Seems like a rather pointless discussion.

For further info, see this thread:
https://www.physicsforums.com/posts/7080456

 

[Andy Resnick]

Late to this thread, but regarding the OP topic- fetal breathing movements do occur in utero, but these are associated with neurological and muscle development and not with gas exchange. It's also possible that fetal breathing movements help coordinate the action of airway cilia so that they all beat in the same direction.

It's worth mentioning that the fetus is also urinating in utero due to kidney development. Make of that what you will....

"First breath" is the most important respiratory event of life, and yet is particularly difficult to study. There are profound changes not just to the airway epithelium (secretory -> absorptive) but also the circulatory system (since the pulmonary arteries need to start functioning) that must occur within seconds.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4526381/

https://www.amazon.com/Textbook-Fetal-Physiology-Geoffrey-Thorburn/dp/0198577486?tag=pfamazon01-20

https://www.amazon.com/Lung-Scientific-Foundations-Ronald-Crystal/dp/0397516320?tag=pfamazon01-20 (chapter 6)

 

[DeBangis21]

Nothing to add, just want to say this is a fascinating thread!


Wow.

Ditto. Plain technical discussions.

 

[sophiecentaur]

TL;DR Summary: How do fetuses breathe in the womb?

If the human fetuses don't breathe in the womb, how do they get their oxygen?

Back to the OP: it's amazing how this is not better known. The misconception is found in many societies and cutures. So much so that in many societies, pregnant women will avoid having a bath in case they 'drown' their unborn baby.

Likewise, new mothers in some societies are discouraged from feeding their new born infant with the (clear) colostrum that the breasts produce initially on the grounds that it is 'bad stuff'. In fact, of course, it is highly suitable for new-borns (surprise surprise)

Also, there are some very strange notions about how, when and where to cut the umbilical cord. As if all other mammals would actually need a pair of scissors! For most mammals, the placenta is delivered shortly after the young arrives and soon just separates all on its own - much to the delight of the waiting crows. Afaik, the first aid device for a DIY human birth is just tl let the placenta sit there until medics arrive.