Detailed Menstrual Cycle – including hormonal changes
The Follicular phase (Day 1 to 14):
This phase lasts from day 1 of your cycle (the start of menstrual bleeding) to roughly day 14 (the ovulation). During the Follicular phase you will notice the menstrual bleeding, but your ovaries are actually also preparing the next ovulation. The pituitary gland in the brain releases FSH (Follicle stimulating hormone). It causes the follicles in the ovaries to proceed to the surface of the ovary. Follicles are fluid-filled sacs which each contain an egg. One of the follicles becomes dominant and develops into an egg. As the follicle becomes more dominant it produces the hormone estrogen, which also triggers a thickening of the endometrium (the lining of the uterus). This estrogen level increase during the egg’s develops and peak just before ovulation. When the levels of estrogen reach the highest levels, it stimulates the production of gonadotropin-releasing hormone (GnRH), which results in the brain making luteinizing hormone (LH). Talking about intricacy: When LH and LSH reach a peak near day 12, the ovaries release a small peak in testosterone which increases libido, just on the most fertile day. Cool right?
By the way, ovulation tests usually measure the levels of LH and LSH in the urine to help determine the most fertile day.
Ovulatory Phase (Day 14)
The peaks of LH and LSH coming together cause the release of the mature egg. The egg travels down the fallopian tube where it is fertilized if there is sperm present.
Luteal Phase (Day 14 to 28)
After the egg is released, the levels of LH and LSH return to normal. The closure of the follicle in the ovaries (corpus luteum) produces progesterone. If the egg is fertilized by a sperm cell the corpus luteum continues to produce progesterone which keeps the endometrial lining from being shed. If the progesterone levels drop when there is no fertilization the endometrial lining is shed during menstruation.
PCOS fact: With PCOS, Polycystic Ovulatory Syndrome there are higher level of LH throughout the cycle. With LH levels being high throughout the cycle there is often no LH peak and therefore no ovulation. It results in a lot of nearly mature follicles (cysts). Hence the name polycystic.