Hormone levels during the menstrual cycle.

For both male and female reproduction, it really helps to remember that the first hormone in the chain is gonadotropin-releasing hormone (GnRH), released by the hypothalamus to stimulate the release of pituitary gonadotropins - follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the anterior pituitary gland. In both males and females these two hormones act to promote gametogenesis and androgen/estrogen secretion.

During the first 11 days of the cycle, estrogen exerts negative feedback control over the secretion of LH and FSH. This decrease in FSH causes the regression of all the follicles except the emerging dominant follicle. Eventually, however, the estrogen levels increase to such a degree that the mode of control regarding LH shifts from negative feedback to positive feedback. In other words, estrogen increases rapidly in the late follicular phase and triggers the LH surge.

Hormonal control of the menstrual cycle is rarely understood from the first source. This is a topic for which learning is really helped by getting a number of narrations.