Menstrual Cycle Phases | Female Reproductive System | Follicular Luteal Proliferative Secretory

The video introduces the topic of the female menstrual cycle, which is covered as part of an NCLEX review series for maternity. The goal is to understand each phase, what happens in it, when it occurs, and the role of hormones.

A typical menstrual cycle is 28 days, with ovulation occurring around day 14. The primary goal of the reproductive cycle is reproduction. The ovaries and uterus work together, undergoing three phases each: Ovarian (follicular, ovulation, luteal) and Uterine (menstrual, proliferative, secretory). These phases are interconnected, with ovarian changes preparing the uterus for potential pregnancy.

The follicular phase (cycle days 1-13) focuses on maturing a follicle and egg for release. The hypothalamus releases gonadotropin-releasing hormone, stimulating the anterior pituitary to release FSH and LH. FSH stimulates follicles to grow, but only one matures into a Graafian follicle. As the follicle grows, it releases estrogen, which initially causes a dip in FSH and LH, but a massive peak of estrogen signals egg readiness, leading to an LH surge.

Corresponding with the early follicular phase, the menstrual phase (cycle days 1-6) is when bleeding occurs as the stratum functionalis layer of the endometrium is shed. This happens because pregnancy did not occur in the previous cycle, causing a drop in progesterone and estrogen levels, initiating a new cycle.

Following the menstrual phase, the proliferative phase (cycle days 7-14) rebuilds the stratum functionalis. Estrogen secreted by the growing follicle drives this rebuilding, preparing the uterus for implantation. Estrogen also thins cervical mucus, making it more sperm-friendly.

Around day 14, the ovulation phase occurs, where the egg is released about 24-36 hours after the LH surge. The ovum is swept into the fallopian tube by the fimbriae, and it lives for 24 hours. The most fertile days are typically cycle days 9-16. If sperm is present, fertilization most commonly occurs in the ampulla of the fallopian tube. A woman's basal body temperature may dip at ovulation and then increase.

The luteal phase (cycle days 15-28) and the uterine secretory phase (cycle days 15-28) work together. After ovulation, the Graafian follicle transforms into the corpus luteum, which acts as a temporary endocrine structure. It secretes large amounts of progesterone and some estrogen to prepare the endometrium for potential implantation. If no pregnancy occurs, the corpus luteum degenerates, leading to a drop in hormones and the start of a new menstrual cycle.

If fertilization and implantation occur, the embryo releases hCG (human chorionic gonadotropin). HCG prevents the corpus luteum from degenerating, allowing it to continue producing progesterone and estrogen to maintain the pregnancy until the placenta takes over around 8-10 weeks.