After puberty human female shows cyclic changes in her reproductive system . Explain structural and hormonal changes in the uterus .

Explanation

(a) Menstrual phase : When the ovum is not fertilized the high level progesterone inhibits secretion of Luteinising Hormone (LH) and LH level decreases . This results in decreases in level of progesterone from corpus luteum. When the amount of progesterone further decreases and stimulates anterior pituitary to secrete Follicle Stimulating Harmone (FSH) and proliferative phase begins the basal part of endometrium remains intact and thickness is only about 1mm.
(b) Proliferative phase : In this phase the primordial follicle of the ovary develops into Graafian follicle . Many primordial follicles are present in the ovary.
Changes in uterus : Oestrogen secreted by follicular cells of ovary stimulate endometrial glands . Thickness of endometrium grows to about 3 mm to 5 mm .
(c) Ovulatory phase : Ovulation is the process in which there is rupture of Graafian follicle with discharge of ovum into abdominal cavity . It is uder influence of LH . A sudden rise in level of LH stimulates ovulation which occurs usually on 14 th day of menstrual cycle .
(d) Secretory phase : Corpus luteun in ovary secrets progesterone . It causes further groeth of endometrial glands . Uterine gland secrets fluid which is rich in glycongen for nourishing the dividing embryo . It is also called uterine milk. Thus , further increases in thickness of endometrium takes place ( 5mm to 6 mm ) . If fertilisation occurs , embryo is implanted in thickened endometrium.