Scarleteen

Hi, this is my first post in Scarleteen.
I had this odd question in my head this afternoon while I was passenger in a Uber car.
When menstruation/period happens, it pulls out the whole uterine lining or a part will stay in the uterus?.
There will be a part of uterine lining that will never be flowed?.

P.D.: Sorry about my english level, I'm not a english-mother language-speaker.

Thanks.

Your English is fine.

Yes, the whole uterine lining comes out during a period. There's more information if you want it about the menstrual cycle here: On the Rag: A Guide to Menstruation