Women and Men's fertility

[mooeypoo]

I was watching a science show about the beginning of new life (yes, sex! ) and I understood that women are fertile (generating eggs) since BEFORE their birth.

 

Anyone knows why so early?

And why - if women are generating eggs since birth - do men only start to generate fertile sperm from puberty onwards?

 

~moo

[Cookie]

Girls are not really "fertile" until puberty either. Fertility requires ovulation, and while girls have all the eggs they'll ever have before they're born, they don't begin ovulating until puberty.

 

And really, to say that girls have "eggs" before they're born is a bit of a misnomer - they actually have follicles, which will, under hormonal stimulation, develop into eggs.

 

Cookie

[Ms. DNA]

Eggs develop from oocytes, which are contained in follicles.

[Glider]

Isn't Oocyte just the biological term for egg?.

[mooeypoo]

Well naturally girls are only fertile when they start to have periods, that wasn't suposed to be my question but it was MY MISTAKE I used the wrong word.

Fertilize shouldn't be the word...

 

The question should be more of - why girls have eggs from such a young age, while buys start to have sperm only in puberty (at least thats what I underrstood from that movie, correct me if i'm wrong...)

[Ms. DNA]

Glider said in post # :

Isn't Oocyte just the biological term for egg?.

 

I've seen the terms used interchangably, but I've also seen "oocyte" used to refer to an immature egg. The precursor cells that produce eggs and sperm have to divide twice (meiosis), and oocytes are "frozen" between cell divisions. One of them each month in a fertile woman will divide again, and one daughter cell will get most of the cytoplasm and form the mature egg. Here's a link:

 

http://www.medfac.leidenuniv.nl/heelkunde_onderwijs/IMM/imm39.html

 

As to mooeypoo's question, I think sperm only survive a few days; they're being constantly created and reabsorbed. It's easier to make sperm than eggs anyway, since you can create four sperm cells from a single precursor. So it wouldn't make sense to store them the way immature eggs are. But someone else here might know more about sperm than I do.

[mooeypoo]

It sounds logical, but still -- if it's easier to make sperm than egg, shouldn't the effect be the other way around? Males starting to produce sperm from birth and females only starting from puberty?

[Ms. DNA]

I should have been clearer about why it's easier to make sperm instead of eggs. Sperm cells do not need as much cytoplasm and associated organelles as eggs do. You can split a precursor cell into four sperm, and they'll all be viable. But an egg needs to retain as much of its cytoplasm and organelles as possible; otherwise, it won't survive. When the precursor of an egg cell goes through meiosis, one daughter cell is almost the same size as the original cell, and the other daughter is very small and consists mostly of genetic material. The small daughter cell is called a polar body; it isn't viable. So if you're making gametes, you can make four sperm from one precursor, but you get only one egg and three polar bodies if you're making eggs. I probably should have said it's more efficient to make sperm, but I was in a hurry to get to lunch.

 

Does that make sense, mooeypoo? And has this answered your question?

[mooeypoo]

It explains why eggs are harder to make than sperm, which (being a female) this sounds obvious. Or, well I'd like to think it's obvious, concidering the "troubles" us girls go through to get the damn egg

 

The think is that if indeed eggs are HARDER TO MAKE then I still don't understand why nature made females start manufacturing them SINCE BIRTH (or even before) if it's OBVIOUS it's not needed until AT LEAST puberty.

Plus, it's a known fact that females have a relatively small amount of eggs for their entire life - so it now sounds even less reasonable that nature would START manufacturing those small amount of eggs at such young and non-needed age of the girl.

 

But thanks, it helped me realise what that "making" process requires

 

~moo

[Cookie]

We don't manufacture eggs throughout our lifetimes. All the eggs a woman will ever have are present at birth. Just a thought though...since eggs are continually lost over a woman's lifetime, maybe it's nature's way of making sure that we're not having babies when we're too old to carry them to term?

 

I don't know...just throwing out ideas - your question is a good one.

 

Cookie

[mooeypoo]

Ahhhhhhh that makes more sense (the "carrying all the eggs a women will ever have" part) kewl, okay now it makes more sense.

 

Though, still, I don't get why biologically the differences between male reproduction and female reproduction are so different.

Maybe because the male is "throwing" around his sperm (in nature, animals do it all the time) in an attempt to fertilize as many females as possible, while females are the "picky" (also, from what I gather its the same with animals) ones who need to actually MAKE the 'best possible child'... or yeh something like that... if that makes any sense.

 

About your question, I have no idea but it sounds true... good one, I'd like to hear an answer too

 

~moo

[BrainMan]

It is just a simple solution to store all the components needed beforehand. It is then just a matter of stimulating the right tissues with reproductive hormones for the eggs to develop fully and be released. The question is not why this happens with females, the question is why this doesn't happen with males.

 

Unlike females, who produce one (or a few) eggs a month, males must be able to produce huge quantities of sperm on the fly. If Iggie the caveman can knock up two different females in a two hour period of time, so much the better for his genes. But all these sperm need the right environment to live in, and dont live very long anyway. If men had all the sperm (along with the proper living environment for those sperm) they would need at birth, they would have to lug around giant sack-like organs the size of a football field. Sadly, if this was the strategy Iggie used, he would not easily have survived in the brutish real world of yester-years.

 

Not a bad just-so story, was it?

[mooeypoo]

Actually quite a good one

 

hehe makes sense.