Reproductive Fact of the Day #4: Which hormones are involved in the menstrual cycle and what do they do?
There are four main players when it comes to hormones involved in the menstrual cycle:
- Estrogens (this a family of hormones, not just a single hormone, for example, estradiol is an estrogen)
- FSH (follicle stimulating hormone
- LH (Luteinizing hormone)
They all have different effects. Estrogen is responsible for stimulating the growth of the endometrium while progesterone maintains it. LH surges and induces ovulation and FSH stimulates the follicles to grow until ovulation.
The day you start your period is considered day 1 of the cycle. Ovulation occurs about 14 days before you start your period, this is the approximate half-way point if your cycle is 28 days long.
At day one, estrogen and progesterone levels are low (because the lining is being shed). LH is also low at day one, but FSH is in the process of stimulating the ovaries to grow a mature follicle (there is a feedback mechanism from the maturing follicle that prevents other follicles from being ovulated and this happens in only one ovary).
A few days prior to ovulation (day 14 on the above chart) estrogen peaks. This induces progesterone to be released to maintain the endometrial lining. LH and FSH both surge at ovulation and the mature follicle (containing the ovum) ruptures, releasing the ovum into the abdominal cavity.
The follicle remnants left behind turn into the corpus luteum which produces progesterone, estrogen, and a substance that inhibits FSH (this makes sense because if we’ve released an egg, we don’t want our follicles to continue to mature in case of pregnancy). The progesterone makes the lining of the uterus thicker for implantation in case of pregnancy.
If no pregnancy occurs, eventually the progesterone stops being produced by the corpus luteum (which atrophies and dies after awhile if pregnancy does not occur), the lining is shed, and the cycle begins again.