Menstrual Flow and Hormones

Progesterone:
Menstrual flow occurs due to a lack of progesterone. Progesterone is a hormone that is produced by the ovaries during the second half of the menstrual cycle. It plays a crucial role in preparing the uterus for a potential pregnancy. If pregnancy does not occur, progesterone levels drop, leading to the shedding of the uterine lining, which results in menstruation.

FSH (Follicle-Stimulating Hormone):
FSH is another hormone that plays a key role in the menstrual cycle. It is responsible for stimulating the growth of ovarian follicles, which contain the eggs. During menstruation, FSH levels are low as the body prepares for the next cycle of egg development.

Oxytocin and Vasopressin:
While oxytocin and vasopressin are important hormones involved in childbirth and water regulation, they do not directly impact menstrual flow. Oxytocin is known as the "love hormone" and is involved in labor and breastfeeding. Vasopressin helps regulate water balance in the body.
In conclusion, the lack of progesterone is the primary factor in initiating menstrual flow. This hormonal imbalance triggers the shedding of the uterine lining, resulting in menstruation. While FSH, oxytocin, and vasopressin play important roles in other physiological processes, they do not directly influence menstrual flow.