Final Study Guide: Menstrual Cycle & Ovulation Process

Menstruation (Menses)

• GnRH and a balance between activin and inhibin from the granulosa cells contribute to the rise of FSH levels, which stimulates a number of follicles.
• The pulsatile secretion of FSH from the anterior pituitary gland rescues a dominant ovarian follicle from apoptosis by days 5 to 7 of the cycle.
• Estrogen and FSH increase FSH receptors in the granulosa cells of the primary follicle, making them more sensitive to FSH.
•  FSH and estrogen combine to induce production of LH receptors on the granulosa cells of the primary follicle, promoting LH stimulation and increasing follicular estrogen secretion.
• As estrogen levels rise, FSH levels drop due to an increase in inhibin-B secreted by the granulosa cells in the dominant follicle.
• The decrease in FSH levels reduces the growth of the less-developed follicles.
• Estrogen causes the cells of the endometrium to proliferate and stimulates production of LH.

• Ovulation marks the beginning of this phase.The ovarian follicle transforms into a corpus luteum.
• Pulsatile secretion of LH from the anterior pituitary stimulates the corpus luteum to secrete progesterone, initiating the secretory phase of endometrial development.
• Glands and blood vessels in the endometrium branch and curl throughout the functional layer, and the glands begin to secrete a thin glycogen-containing fluid. If conception occurs, the nutrient-laden endometrium is ready for implantation.
• Human chorionic gonadotropin (HCG) is secreted 3 days after fertilization by blastocytes and maintains the corpus luteum after implantation, which occurs around day 6 or 7.HCG can be detected in maternal blood and urine 8 to 10 days after ovulation.

• The production of estrogen and progesterone continues until the placenta can adequately maintain hormonal production.
• If conception and implantation do not occur, the corpus luteum degenerates and ceases production of progesterone and estrogen.
• Without progesterone or estrogen to sustain it, the endometrium becomes ischemic and disintegrates, leading to menstruation and the start of a new cycle.

• Ovulatory cycles typically last between 24 to 26.5 days.
• The primary ovarian follicle requires 10 to 12.5 days to develop.
• The luteal phase is relatively fixed at 14 days (+/- 3 days).
• Menstrual blood flow usually lasts 3-7 days but can range from 1 to 8 days and still be considered normal.