What is the relationship between the estrogen level and the LH level in the menstrual cycle? What is the function of LH in the menstrual cycle and when does its blood concentration reach a peak?

The enhance in the blood concentration of estrogen with the growing of the ovarian follicle causes the hypophysis to secrete LH. In this phase LH acts together with FSH promoting the maturation of the follicle that at the 14th day ruptures releasing the female gamete (ovulation). After the release of the ovum LH acts stimulating the formation of the corpus luteum, a structure made from the remaining follicular mass. The LH concentration is at maximum at the 14th day of the cycle.