Read the graph given above and correlate the uterine events that take place according to the hormonal levels on
(i) 6 - 15 days
(ii) 16 - 25 days
(iii) 26 - 28 days (if the ovum is not fertilised )
(b) Specify the sources of the hormones mentioned in the graph.

Explanation

(i) It is the follicular phase where the FHS stimulates the overian follicles to secrete estrogen which in ture stimulates the proliferation of the endometrium of the uterine wall . The endometrial lining begins to thicken.
(ii) Secretion of progesterone maintains the endometrium which is neccessary for implantation of fertilised ovum and other events of pregnancy.
(iii) When fertilisation does not take place, the endometrium, disintegrates, leading to menstruation making a new cycle.
(iv) Oestrogen is secreted by the ovarian follicle and progesterone is secreted by the corpus luteum.