The Menstrual Cycle Consists of Two Interconnected Cycles
- The ovarian cycle, which focuses on egg development and release.
- The uterine cycle, which prepares the uterus for a potential pregnancy.
The Menstrual Cycle
The menstrual cycle is a recurring sequence of physiological changes in the female reproductive system, typically lasting about 28 days, that prepares the body for potential pregnancy.
Remember: FSHand oestradiol work together to prepare the egg and the uterus for potential fertilization.
Hormones Are The Key Players in the Menstrual Cycle
- To understand the menstrual cycle, it’s essential to know the primary hormones involved and their roles.
- These hormones interact through positive and negative feedback mechanisms to regulate the ovarian and uterine cycles:
Follicle-Stimulating Hormone (FSH)
Stimulates the growth of ovarian follicles and oestradiol production.
Luteinizing Hormone (LH)
Triggers ovulation and supports the formation of the corpus luteum.
Oestradiol
A form of estrogen that promotes the growth of the uterine lining (endometrium) and regulates FSH and LH via feedback loops.
Progesterone
Maintains the endometrium, preparing it for implantation, and inhibits FSH and LH to prevent new follicle development.
Don't let "oestradiol" throw you off, it is used officially (and more specifically) to mean "estrogen"
The Ovarian Cycle Is A Three-Stage Process Involving Egg Development and Release
1. Follicular Phase (Days 1–14)
- FSH Stimulates Follicle Growth: Multiple follicles begin to develop in the ovary, but only one becomes dominant.
- Rising Oestradiol Levels: The maturing follicle produces increasing amounts of oestradiol, which promotes follicle development and thickens the uterine lining.
- Positive Feedback: High oestradiol levels trigger a surge of LH.
- Associate positive feedback with a "green light" (LH surge leading to ovulation)
- Associate negative feedback with a "red light" (progesterone preventing new follicle development).
2. Ovulation (Day 14)
- LH Surge: The surge in LH causes the dominant follicle to rupture, releasing the egg into the oviduct (fallopian tube).
- Completion of Meiosis: The oocyte completes the first stage of meiosis, preparing it for fertilization.
