What Triggers Your Cervix to Close?

What is it that triggers your cervix to close after your period? Does it get a message from your uterus that it is empty? Is it on a timer? Guessing no because some people have short periods and some have long? So how does it know when to close! Google isn't helping me and I'm curious. I've been thinking about it all because I usually only have two to three days of menstrual flow and during this particular cycle I happened to notice my cervix was high and closed basically at the end of day two of bleeding. Why do some woman have short periods and some long? Is it an indication of anything?

Anyone??

Hormones. They're on a cycle, different for everyone.

I'd say it is more the trigger telling it to open (hormones) has disapeared.

Here's a quick pic showing the process -

3599

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Here's a quick pic showing the process -

3599

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Hahah

Awesome Keike. Really informative :)