Menstruation.cycle

Question

Peaks of LH and FSH production occur during

1.the menstrual.flow phase of the uterine cycle.

2.the beginning of the follicular phase of the ovarian cycle.

3.the period just before ovulation.

4.the Secretary.phase of the uterine cycle

Answer 1

In order to fully understand the events of the menstrual cycle, it's important to look at a graph that shows the amount of each hormone over time - any decent anatomy or physiology textbook will display this information. Best of all is when you can draw this graph on your own and understand how it works. It should include at least FSH, LH, estrogen, and progesterone and ideally would have gonadotropin releasing hormone and possibly inhibin as well.

You should also understand which structures (hypothalamus, pituitary gland, follicle, corpus luteum) produce all of the hormones and understand the functions of these structures.

It's also important to understand how each of the hormones affects the others. Does a hormone inhibit or promote a different hormone?

During the menstrual phase of the uterine cycle (the first few days of the monthly cycle which is also equivalent to the follicular phase of the ovarian cycle) FSH and LH are low, having been suppressed by estrogen and progesterone at the end of the previous cycle. They rise slowly during the follicular phase (FSH stimulates follicle growth) but maintain low levels because low levels of estrogen keep them from rising too high. As the follicle grows under the influence of FSH, more estrogen is produced.

The key event that triggers ovulation (around day 14 of the cycle) is a massive spike in LH. FSH spikes as well, but to a much lesser degree. GnRH production (which promotes FSH and LH) has been building during the first two weeks, but only once estrogen gets to a high enough level (after being released by the follicle) are FSH and LH released.

Post-ovulation (secretory phase), FSH and LH are inhibited by estrogen and especially progesterone. During this time the uterus is preparing for implantation of a fertilized embryo. The ovarian hormones (E & P) are produced by the corpus luteum which is formed after ovulation - this prevents a new follicle from forming which would not be necessary after an oocyte is ovulated and ready to be fertilized.