Menstrual flow onset caused by?

[m25]

Does decreased level of estrogen alone during the luteal phase cause the onset of menstrual flow, or is it the decreased level of both estrogen and progesterone that causes the onset of menstrual flow?

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[tdod]

Does decreased level of estrogen alone during the luteal phase cause the onset of menstrual flow, or is it the decreased level of both estrogen and progesterone that causes the onset of menstrual flow?

I am not sure about this, but my understanding is that E & P are high during the luteal phase b/c they are being secreted by the corpus luteum. however, the corpus luteum eventually dies (unless pregnancy occurs) and ceases to secrete E & P. Progesterone is important for encouraging the endometrium to continue growing; I would assume that, without progesterone, the endometrium is shed.

 

[Hadi7183]

@tdod is right. Progesterone is essential for the maintenance of endometrium ; reduced progesterone level --> menstruation.