Explanation

In menstrual phase, the production of LH and progesterone decreases. Menstrual cycle [table] Phases | Days | Events ; Menstrual phase | 1-5 | Endometrium breaks down, menstruation begins. The cells of endometrium, secretions, blood and the unfertilized ovum constitute the menstrual flow. Progesterone and LH production is reduced ; Follicular phase (proliferative phase) | 6-13 | Endometrium rebuilds, FSH secretion and oestrogen’s secretion increase ; Ovulatory phase | 14 | Both LH and FSH attain a peak level. Concentration of oestrogen in the blood is also high and reaches its peak, Ovulation occurs ; Luteal phase (secretory phase) | 15-28 | Corpus luteum secretes progesterone. Endometrium thickens and uterine glands become secretory [/table]