Q. What event marks the beginning of the menstrual cycle? What is the blood concentration of FSH, LH, estrogen and progesterone in this phase of the cycle?
By convention the menstrual cycle begins at the day that menses begins and Menses is the endometrial hemorrhage excreted through the vaginal canal. At these days the hormones LH, FSH, progesterone and estrogens are in low concentration.