Explain the following phases in the menstrual cycle of a human female :
(i) Menstrual phase
(ii) Follicular phase
(iii) Luteal phase

Explanation

(a) (i) The cycle starts with the menstrual phase when menstrual flow occurs and its losts for 3-5 days . The menstrual flow results due to break down of endometrial lining of the uterus and its blood vessels which forms liquid that comes out through vagina.
(ii) The menestrual phase is followed by the follicular phase. During this phase , the primary follicles in the ovary grown to become a fully mature graffian follicle and simutaneusely the endometrium of uterus regenerates through proliferation . the secretion of gonadotropins increase gradually during the follicule phase and stimulates follicular development as well as secretion of estrogens by the growing follicles.
(iii) Luteal phase during which the remairing part of the graffian follicle transfrom as the corpus luteum . the corpus luteum secretes large amounts of progesterone which is essential for maintenance of the endometrium.