The Menstrual Cycle
Explaining the menstrual cycle; By: Morgan Simpson
How each hormone level factuates throughout the cycle:
- FSH: In the begining of the cycle FSH starts low then get higher, but then drifts slightly down. Then it reaches its peak and gradually falls down.
- LH: In the begining of the cycle LH starts the same way as FSH, but then it surges up just before clay 14. It is this surge in LH that triggers ovulation.
- Estrogen: When the cycle starts the increasing levels of FSH bring about the maturation of the ovarian follicle. The follicular cells in turn produce increasing levels of estrogen.
- Progesterone: The corpus luteum starts producing increasingly higher levels of progesterone, it also starts producing increasingly higher levels of estrogen.
Hormone level picture citation:
How do endometrial lining change due to hormones?
Description of follicular development based on hormones:
In women, when hormone levels fall towards the end of the menstrual cycle, this is sensed by nerve cells in the hypothalamus. These cells produce more gonadotrophin-releasing hormone which in turn stimulates the pituitary gland to produce more follicle stimulating hormone and luteinising hormone and release these into the bloodstream. The rise in follicle stimulating hormone stimulates the growth of the follicle in the ovary. With this growth, the cells of the follicles produce increasing amount of oestradiol and inhibin. In turn, the production of these hormones is sensed by the hypothalamus and pituitary gland and less gonadotrophin-releasing hormone and follicle stimulating hormone will be released. However as the follicle matures, and more and more estrogen is produced from the follicles, it simulates a surge in luteinising hormone and follicle stimulating hormone which stimulates the release of an egg from a mature follicle – ovulation.
In men, the production of follicle stimulating hormone is regulated by the circulating levels of testosterone and inhibin, both produced by the testes. Follicle stimulating hormone regulates testosterone levels and when these rise they are sensed by nerve cells in the hypothalamus so that gonadotrophin-releasing hormone secretion and consequently follicle stimulating hormone is decreased. The opposite occurs when testosterone levels decrease. This is known as a negative feedback control so that the production of testosterone remains steady. The production of inhibin is also controlled in a similar way but this is sensed by cells in the anterior pituitary gland rather than the hypothalamus.
How do hormone levels change during pregnancy?
Pregnant women experience sudden and dramatic increases in estrogen and progesterone, as well as changes in the amount and function of a number of other hormones. These changes can not only affect mood, they can also create the “glow” of pregnancy, significantly aid in the development of the fetus, and alter the physical impact of exercise and physical activity on the body.