Term 2 Topic - Menstrual Cycle

In my opinion, Biology was easier topic, because understanding concepts were more important than just pure memorization, unlike in Chemistry. However, there were still topics like menstrual cycle, reproductive system and fetal development.

In this post, I will be talking about Menstrual Cycle.

Firstly, there are 5 hormones involved in the menstrual cycle:
1. Gonadotropin Releasing Hormone
2. Follicle Stimulating Hormone
3. Luteinizing Hormone
4. Estrogen/Oestrogen
5. Progesterone


Follicle Stimulating Hormone comes from the brain, released at the start of the cycle. The anterior pituitary gland secretes Follicle Stimulating Hormone and it travels to the ovaries through the blood stream. It binds to the ovaries and stimulates the development of follicles (immature egg with protective layer). Follicle Stimulating Hormone is only responsible for growing the follicle.

The granulosa cells of the follicle secrete Estrogen. Granulosa cells forms around the growing follicle. Estrogen goes to both the uterus and the anterior pituitary gland. It stimulates repair and development of the uterus lining (endometrium). It goes to the anterior pituitary gland and inhibits secretion of Follicle Stimulating Hormone. (Stops the secretion of Follicle Stimulating Hormone)

After a high level of estrogen level, the estrogen stimulates the anterior pituitary gland to produce Luteinizing Hormone. Luteinizing Hormone goes to the ovary where it causes ovulation. Luteinizing Hormone stimulates the Graaffian follicle to release the secondary oocyte (mature egg). The other parts of the Graaffian follicle are stimulated by Luteinizing Hormone to develop into the corpus luteum. The corpus luteum will secrete estrogen, and a new hormone called progesterone.

Progesterone stimulates the uterus to maintain the thickening of the endometrium (uterus lining). In the anterior pituitary gland, Progesterone inhibits the secretion of Luteinizing Hormone. As long as the corpus luteum is there, there will be neither Follicle Stimulating Hormone nor Luteinizing Hormone. The corpus luteum lasts for around 14 days.

If there is no fertilization, the endometrium will break down, and the body will discharge it as blood. This cycle then repeats.