How does menstruation proceed during one period?
The answer is both. Different women experience menstruation differently depending on the levels of different hormones in their body, personal medical conditions, medications, on their age, and the activities they do in their lives. Bleeding is due to the sloughing off of the highly vascularized endometrial lining of uterus which is no longer receiving the appropriate levels of progesterone for its maintenance from the corpus luteum, in the absence of an implanted embryo in the uterus. You can imagine how different this common event would be if a woman was taking warfarin, had a bleeding or coagulation disorder, had polycystic ovarian syndrome, was a runner, or was a 13-year-old vs a 41-year-old. It varies!

Source:


Welt et al. Physiology of the Normal Menstrual Cycle. Last updated Feb 28, 2014. http://www.uptodate.com/contents/physiology-of-the-normal-menstrual-cycle. 
http://www.womenshealth.gov/publications/our-publications/fact-sheet/menstruation.html