Menstrual Cycle Physiology: the Uterine Cycle

The endometrium has receptors for ovarian hormones! Changes in structure and secretory capacity of the endometrium occur in response to hormonal changes in the ovarian cycle.

Note: The drop in progesterone concentration that triggers menses is the physiologic basis of the progesterone withdrawal challenge

(used to test if a woman is hypo-estrogenized). If a woman is making estrogen (i.e. if ovaries/follicles are functioning), endometrium will be built up, so a short course of progesterone (10-14 days) will induce menses within 3 days once the progesterone is stopped. If woman is hypo-estrogenized (i.e. ovarian failure, menopause) -> no endometrium -> no menses upon termination of progesterone.



Note: The drop in progesterone concentration that triggers menses is the physiologic basis of the progesterone withdrawal challenge (used to test if a woman is hypo-estrogenized). If a woman is making estrogen (i.e. if ovaries/follicles are functioning), endometrium will be built up, so a short course of progesterone (10-14 days) will induce menses within 3 days once the progesterone is stopped. If woman is hypo-estrogenized (i.e. ovarian failure, menopause) -> no endometrium -> no menses upon termination of progesterone.



 • The days of high blood progesterone concentration leads to: Death of the outer endometrium tissue, Hemorrhaging of blood vessels in endometrium; washes dead tissues out through vagina -> Menses (shedding of endometrium)

 • Estrogen secreted during the follicular phase stimulates endometrial growth: Endometrial cells enlarge and divide, Blood vessel networks in the endometrium expand, # of progesterone receptors incr -> Readies endometrium for implantation

 • Progesterone from the corpus luteum stimulates endometrial secretion of: Nutrient-rich mucus, Incr glycogen content -> Provides a suitable, nutritious substrate for the (possibly fertilized) ovum



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