Which hormones are secreted by the anterior pituitary to regulate the menstrual cycle? Select all that apply.

The endometrial cycle aligns with the ovarian cycle and consists of three main phases: menstrual, proliferative, and secretory. The secretory phase coincides with the luteal phase of the ovarian cycle and spans approximately days 15–28. It is regulated primarily by progesterone (normal mid-luteal: 5–20 ng/mL) secreted by the corpus luteum. Progesterone stimulates the endometrial glands to secrete glycogen and other nutrients, making the endometrium thick, vascular, and receptive to implantation. Without fertilization, progesterone levels fall, leading to endometrial breakdown and the start of menstruation.

Rationale for correct answer

C. The secretory phase is driven by progesterone from the corpus luteum and prepares the endometrium for possible implantation. It occurs during the luteal phase of the ovarian cycle.

Rationale for incorrect answers

A. The menstrual phase coincides with the early follicular phase, not the luteal phase. It involves shedding of the functional layer of the endometrium due to hormone withdrawal.

B. The proliferative phase occurs during the follicular phase of the ovarian cycle. It is estrogen-driven and involves rebuilding the endometrium after menstruation.

D. The regenerative phase is not a standard term in the clinical classification of the endometrial cycle. The correct phases are menstrual, proliferative, and secretory.

Take home points

• The secretory phase matches the luteal phase and prepares the uterus for implantation.
• Progesterone from the corpus luteum drives the secretory changes.
• The proliferative phase aligns with follicular phase and is estrogen-dependent.
• Menstrual phase begins with hormone withdrawal and marks the end of the luteal phase.

The menstrual cycle is divided into the menstrual, follicular, ovulatory, and luteal phases, regulated by hormonal fluctuations of estrogen, progesterone, FSH, and LH. The menstrual phase begins on day 1 of the cycle and lasts about 3–7 days, during which the functional layer of the endometrium is shed due to a sudden drop in progesterone (from normal mid-luteal values of 5–20 ng/mL to <1 ng/mL) after corpus luteum regression. FSH (normal: 3–20 IU/L) begins to rise to recruit new follicles. Blood loss ranges from 30–80 mL, and prostaglandins contribute to uterine contractions and cramping.

Rationale for correct answer

D. The menstrual phase involves the shedding of the functional layer of the endometrium due to the withdrawal of progesterone and estrogen. It marks the beginning of a new cycle.

Rationale for incorrect answers

A. The follicular phase follows menstruation and involves regeneration of the endometrium under the influence of rising estrogen levels from developing follicles.

B. Ovulation is the release of an ovum due to the LH surge, around day 14. The endometrium is not shed during this phase; it continues to thicken in preparation for implantation.

C. The luteal phase occurs after ovulation and is marked by progesterone secretion from the corpus luteum to maintain the endometrium. Shedding occurs only if implantation does not happen.

Take home points

• The menstrual phase is when endometrial shedding occurs due to hormonal withdrawal.
• Estrogen and progesterone drop sharply, triggering menstruation.
• The follicular phase is for endometrial regeneration, not shedding.
• Luteal phase maintains the endometrium; shedding starts only if it ends.