Explain the changes that occur in the ovary and uterus during menstrual cycle in human females. Mention the influence of pituitary and ovarian hormones in bringing these changes.
[5 marks]

Menstrual cycle:

1. In a life cycle, a woman’s body is vulnerable to a variety of changes. The cycle of these changes occur in women every month, positively for pregnancy is called the menstrual cycle.
2. When an ovum is unfertilised, the uterus lining sheds and leads to a haemorrhage, called menstruation.
3. The duration of a menstrual cycle is usually 28 days. But, under different physiological conditions, it may vary anywhere between 20 and 40 days.

Changes in ovaries and uterus in menstrual cycle:

1. The menstrual cycle is divided into four phases- menstrual phase, follicular phase, ovulatory phase and luteal phase.
2. Menstrual phase- day 1, uterus lining which is prepared for implantation starts to shed which lasts 3 to 5 days.
3. Follicular phase- in this phase, the primary follicle starts developing into a mature Graffian follicle. The endometrium (the inner lining of the uterus) also starts proliferating. The uterus starts preparation for another pregnancy.
4. Ovulatory phase- mid-cycle phase, this is the phase in which ovulation takes place i.e., day 13-17. The end of the follicular phase along with the ovulation period defines the fertilisation period.
5. Luteal phasei It is the post-ovulation phase, where the fate of the corpus luteum is decided. If fertilisation occurs, pregnancy starts. If fertilisation doesn’t occur, it marks the onset of another cycle.

Influence of the pituitary and ovarian hormones:

1. Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) are secreted by the anterior pituitary.
2. FSH stimulates the growth of ovarian follicles that secrete estrogen.
3. Progesterone is secreted by the corpus luteum.
4. The secretion of FSH and LH gradually increases during the follicular phase.
5. They stimulate the development of follicles and the release of estrogen from them.
6. Estrogen stimulates the proliferation of the endometrium. (Follicular phase)
7. The level of LH and FSH peaks in the middle of the cycle.
8. LH induces ovulation. (Ovulatory phase)
9. There is a sudden surge in LH level just before ovulation.
10. After ovulation, the ruptured follicle develops into the corpus luteum, which secretes progesterone, hence the level of progesterone increases in the luteal phase.
11. Progesterone is required for the maintenance of the endometrium for implantation.(Luteal phase)
12. In the absence of fertilisation, corpus luteum regresses and progesterone level decreases.
13. It leads to the disintegration of the endometrium and menstrual flow occurs.(Menstrual phase)

Diagram:

Diagram: Changes in uterus, ovaries, ovarian hormones and pituitary

hormones in menstrual cycle. ​