Science Dumb, basic questions on Mammalian/human reproduction systems

[raharris1973]

Hey all. In the mammalian male, I understand that from puberty onward, through death, males of the species constantly produce viable sperm and exhibit secondary sex characteristics. Hormone levels may drop along with sperm counts and sperm quality, but the males keep "shooting live rounds".

For the mammalian female, it is my understanding, and correct me if I am wrong, that all the eggs that will ever be produced, are produced and present in the body, in the ovaries, at the point of birth. No new eggs are produced throughout life. This is long before female puberty and the development of secondary sex characteristics.

What happens post puberty in the monthly cycle of ovulation is the release of existing eggs to where they can be exposed to fertilization. When fertilization doesn't happen, you have menstruation. The onset of puberty/ovulation coincides with hormonal changes and development of secondary sex characteristics. Ovulation and menstruation eventually end with menopause.

Has it ever been determined what happens in mammals when the entire stock of eggs are removed or ovaries are removed from the female, pre-puberty? Does that prevent puberty, hormonal changes, development of secondary sex characteristics, and menstruation, or does it leave those processes undisturbed? The body doesn't begin to produce substitute eggs does it? I'm not certain if a procedure for removing *all* eggs from the ovaries while leaving those organs intact and leaving none behind has been devised. Does anybody know?

We know that in mammals, even humans, extraction of some eggs and their cryogenic preservation, and their later reinstallation and fertilization is possible, with some degree of success, but I don't know the age of the youngest eligible patients for extraction, and I suspect that the fraction of the egg stock extracted is never more than a sub-sub-decimal percent of the total.

 

[Bear Ribs]

There's actually some very tentative evidence that the old dogma that a woman never produces new eggs is incorrect. In 2004 there was a study by Tilly that showed that mice could grow new eggs, though this was hotly disputed because science doesn't like anybody going against the orthodoxy. In 2016 more information came out suggesting human ovaries also grow new eggs, but this is some really tentative "Huh, that's weird" level data, nothing concrete.

Scientific evidence suggests women’s ovaries can grow new eggs - Global Women Connected

A new study has found the first evidence that suggest the number of eggs a woman is born with, is not all they’ll ever have. The dogma is that the human ovary has a fixed population of eggs and that no new eggs form throughout life. Until now we believed that when the number of...

www.globalwomenconnected.com

 

[Bacle]

There's actually some very tentative evidence that the old dogma that a woman never produces new eggs is incorrect. In 2004 there was a study by Tilly that showed that mice could grow new eggs, though this was hotly disputed because science doesn't like anybody going against the orthodoxy. In 2016 more information came out suggesting human ovaries also grow new eggs, but this is some really tentative "Huh, that's weird" level data, nothing concrete.

Scientific evidence suggests women’s ovaries can grow new eggs - Global Women Connected

A new study has found the first evidence that suggest the number of eggs a woman is born with, is not all they’ll ever have. The dogma is that the human ovary has a fixed population of eggs and that no new eggs form throughout life. Until now we believed that when the number of...

www.globalwomenconnected.com

If women can produce new eggs, even at a slow rate, that changes a lot when it comes to fertility treatments.

It would mean a lot for older women who still want kids if they knew that certain foods or supplements might allow them to regen eggs faster or push off menopause.

Still want to see more evidence besides a few tentative studies, because if that is true, it should show up on a wider scale if people are actually looking for it now.

 

[bintananth]

When fertilization doesn't happen, you have menstruation. The onset of puberty/ovulation coincides with hormonal changes and development of secondary sex characteristics. Ovulation and menstruation eventually end with menopause.

You are very wrong about menstruation and menopause.

Both are actually quite rare among mammals. Only sixteen mammal species are known to have a menstrual cycle. Of those only two aren't primates or bats. The females of only three mammal species are known experience menopause: humans, killer whales, and pilot whales.

 

[raharris1973]

You are very wrong about menstruation and menopause.

Both are actually quite rare among mammals. Only sixteen mammal species are known to have a menstrual cycle. Of those only two aren't primates or bats. The females of only three mammal species are known experience menopause: humans, killer whales, and pilot whales.

Thanks for the details.

The rest of the mammals aside from the three menopausal ones are fertile unto death?

Do they have anything to substitute for menstrual cycle, or lack the uterine tissue build-up that occurs in menstruating mammals.

Am I correct or not on the 'no new eggs after birth' concept?

Is the distinction between a pre-pubescent and post-pubescent (sexually mature) stage universal among all mammal males and females, or does it vary by species?

 

[bintananth]

I'll try to answer all of these as best I can ...

Thanks for the details.

The rest of the mammals aside from the three menopausal ones are fertile unto death?

AFAIK, yes. For menopause to be a benificial survivial trait the species needs to be social enough and long-lived enoughed with a long enough juvenile period that it's better for grandma to help with her grandkids instead of giving birth again.

Do they have anything to substitute for menstrual cycle, or lack the uterine tissue build-up that occurs in menstruating mammals.

Most mammal species have an estrous cycle or mating season where it's pretty obvious to the males that the females are fertile.

Am I correct or not on the 'no new eggs after birth' concept?

I don't know. Possibly.

There's a species of nematode (Caenorhabditis elegans, IIRC) which has only 1,001 cells, including eggs, when mature. Males can fertilize hermaphrodites. Hermaphrodites can only self-fertilize. There are no females.

Is the distinction between a pre-pubescent and post-pubescent (sexually mature) stage universal among all mammal males and females, or does it vary by species?

Most mammal species have either very obvious visual secondary sexual characteristics when mature (a lion's mane, a man's beard, a woman's breasts*, antlers, &c) or don't have any aside from overall size or taking a look at the neither regions. Prior to puberty there's not much difference in outward appearance aside from the neither regions.

*Human women have enlarged mammaries when they aren't nursing. That's pretty much a human-only trait.

 

[WolfBear]

@raharris1973 If you don't mind, I want to ask a new question here on roughly the same theme, but on a different sub-topic:

If a man gets the entire scrotal part of his vas deferens surgically removed (he can also get a bilateral epididymectomy as a part of this package), just how easy/difficult would be to inject RISUG/Vasalgel (a new form of male birth control) into the abdominal part of this man's vas deferens? And would this RISUG/Vasalgel permanently stay there or ever slip out of this man's abdominal vas deferens?