I’m pretty sure I’ll get my terminology wrong, but here goes.
How does the blood/uterus lining detach from the uterine wall ? What mechanism is used ?
Is it just lots of little muscle contractions (which we feel as cramps) that sort of shake the lining off, or does it peel off due to a hormone, or something else entirely ?
Thanks in advance.
You’re kidding, right? You can get to SDMB and you can’t get to Google? Did you forget to pay the bill this month?
The Museum of Menstruation ( I kid you not ).
Menstruation: The Biological Details. This one seems to answer your detailed O.P. better than the other two, but I will leave them in there anyway.
Cultural Perception of Menstruation
Personally, since I’m a maleDoper, the sum total of my Menstrual knowledge is best presented by this word-on statement delivered to me once by the Wifestrocity:
:eek: MESSAGE RECIEVED !
Hope this helps stamp out some Menstrual Ignorance. ( I just had to find a way to write the word “menstrual” just one more time in this thread. Oops, there I did it again.) 
Cartooniverse
Thank you for the links, Cartooniverse. The third link did contain the answer to my question, which if anybody else is interested, is hormones.
FWIW, I did try Google, but I’m obviously not as talented a googler as you, so please accept my deepest and most humble apologies. [/sarcasm]
I came up with plenty of sites about menstruation… my god there’s a lot out there, but didn’t come across one that specifically answered my question. So thank you for finding one that did, but please don’t assume that I didn’t check first. I did, and came up with many sites like the others you offered which don’t answer my question.
With wings she didn’t like? Huh. Well, I suppose I can see it being an issue if you are somehow going to show the outside of the panties to anyone, but for safety’s sake give me wings any day!!!
–Nenya Elizabeth, chiming in with her TMI dose for the day
I like the way the Evil Nazi Groundhogs worked their way in here.
Damn, those guys are everywhere.
I’m sorry, Goo. I was being a bit too much of a wise-ass for a G.Q. Thread. I should have just offered the info I found without the cracks. Finding the site that offers the best info is the most gratifying PART of Googling, and if we all cast our minds back to the dark fetid days BEFORE Google, we’ll once again kneel down and bow our heads and say a hearty thank you to the Powers That Be for inventing Google at all, because IMHO there is NO way to have found that site, without using as intuitive a search engine as Google.
Anyway, I am sorry, I didn’t mean to snipe at you so hard. 
But then, it wouldn’t be the Straight Dope, it’d be Ask Marylyn Savant ( heaven help us all ). :eek:
Cartooniverse
No worries, Cartooniverse, I bit hard too, when I probably shoulda let it slide. Hopefully my googling will get to your level soon
Thanks again for the info, my new wise-ass friend
And, to give a much more thoughtful and rigorously looked into answer to your O.P., it seems that while the site I gave you gives a good explanation of what CAUSES the sloughing off, the exact mechanism seems to me to sound almost like Losing a scab. Once the connective cellular layers are rendered useless, the body literally lets go of that material.
In the case of the scab, it falls away cleanly since it’s dry and crusty by that time. In the case of the uterine lining, it’s a bit slower and, shall we say, more cumbersome. I guess due to the slight variations in the death of individual cells, instead of having the blood-rich tissue lining the uterus be expelled all at the same time ( a la the Placental Delivery post-partum ), it happens in shreds and bits over a few days, typically. The endocrine system may trigger it’s release of the tissues, but they all slough off at slightly different moments. ( If I had a method of predicting exactly WHEN most of it would slough off, I’d be a wealthy man and the Prince of Periods )
Also, now that I read that last graph, I realize that the Placenta is not rooted along the entire surface of itself to the uterine wall, but rather is linked in only one spot, the Umbilicus. It makes for an easier departure.
Let us walk through the Gardens and contemplate the meaning of this, Grasshopper… so much to learn…
[Amusing Mentor Moment here, the other 22,000 of you may just move along. Nothing to see here, nothing at all… 
)
Re : the extra bonus information. Thanks, and I bet you now know way more about the sloughing of the uterine wall than you ever wanted to. Now go dazzle the wife with your knowledge and understanding, O Master.
Cool, I always wanted to be someone’s grasshopper when I was growing up