Q. Which one of the following events is correctly matched with the time period in a normal menstrual cycle?
(a) Release of egg: 5th day
(b) Endometrium regenerates: 5-10 days
(c) Endometrium secretes nutrients for implantation: 11-18 days
(d) Rise in progesterone level: 1-15 days
Solution :
Correct option : B The menstrual cycle can be divided into four phases: menstruation, proliferative, ovulatory and secretory phase. Day 1-5 (menstruation phase) experience lower estrogens and progesterone level, which in turn results in disintegration of endometrium and menses. Day 5-13 (proliferative phase) is marked by endometrium thickening under influence of estrogens as secreted by developing follicle. Ovulation refers to rupture of mature Graafian follicle and release of ovum/egg in body cavity on 14th days of 28 days menstrual cycle. Ovulatory phase is followed by luteal phase (day 15-28) in which LH stimulates the formation of corpus luteum from ovulated Graafian follicle, which in turn secretes estrogens and progesterone. In absence of fertilization, progesterone and estrogens exert negative feedback control over the anterior pituitary’s secretion of LH and cause degeneration of corpus luteum in the ovary within 10 days of its formation .The lower progesterone level, as caused by the disintegration of corpus luteum, results in disintegration of endometrium thereby initiating the next menstrual cycle (day 1-5). A progesterone level is at peak during day 15-28 (the secretory phase) and is at minimum/absent during menses (day1-5).Endometrial stromal cells contain lipids, glycogen, oxygen and essential minerals, which provide nutrition to developing embryo from the day of implantation (5th / 7th day of ovulation) to first eight weeks of pregnancy. Placenta takes over the function of providing nutrition to the fetus during the second trimester. Thus, the correct answer is option B.
