Menstrual cycle

Question 1

Which cells do FSH and LH act on?

Answer 1

FSH –> granulosa cells to stimulate follicle growth, permit the conversion of androgens to oestrogens and stimulate inhibin secretion
LH –> theca cells to stimulate production and secretion of androgens

Question 2

What feedback do low-moderate oestrogen levels have?

Answer 2

Negative feedback on the hypothalamus and the anterior pituitary gland.

Question 3

What feedback do high oestrogen levels in the absence of progesterone have?

Answer 3

Positive feedback on the HPG axis.

Question 4

What feedback do high oestrogen levels in the presence of progesterone have?

Answer 4

Negative feedback on the HPG axis

Question 5

What is the effect of inhibin?

Answer 5

Secreted by granulosa cells to selectively inhibit FHS secretion.

Question 6

When in the cycles in the follicular phase?

Answer 6

Days 1-14

Question 7

When in the cycles in the luteal phase?

Answer 7

Days 15-28

Question 8

In a 28-day cycle when does ovulation occur?

Answer 8

Day 14 (14 days before first day on menstrual period).

Question 9

What causes the LH surge during the follicular phase?

Answer 9

Oestrogen levels rise enough to have a positive feedback on the HPG axis.

Question 10

Why does FSH not surge with the LH surge?

Answer 10

Inhibit secreted by granulosa cells selectively inhibits FSH secretion.

Question 11

What is meant by leutinisation of granulosa cells?

Answer 11

Granulosa cells begin to express LH receptors.

Question 12

What is the effect of the LH surge on the dominant follicle?

Answer 12

The follicle ruptures and the mature oocyte is assisted to the fallopian tube by fimbria. Here it remains viable for fertilisation for around 24 hours.

Question 13

What happens to feedback on the HPG axis following ovulation?

Answer 13

Negative feedback.
The follicle remains luteinised, secreting oestrogen and now also progesterone, reverting back to negative feedback on the HPG axis.

Question 14

What is the corpus luteum?

Answer 14

The tissue in the ovary that forms at the site of a ruptured follicle following ovulation. It produces oestrogens, progesterone and inhibin to maintain conditions for fertilisation and implantation

Question 15

What does the corpus luteum produce?

Answer 15

Oestrogens, progesterone and inhibin to maintain conditions for fertilisation and implantation

Question 16

What happens to the corpus luteum if fertilisation does not occur?

Answer 16

The corpus luteum spontaneously regresses after 14 days. There is a significant fall in hormones, relieving negative feedback, resetting the HPG axis ready to begin the cycle again.

Question 17

In case of fertilisation, what secretes hCG?

Answer 17

The syncytiotrophoblast of the embryo produces human chorionic gonadotropin

Question 18

What is the function of hCG?

Answer 18

A luteinising effect, maintaining the corpus luteum.

Question 19

Describe the pattern of oestrogen levels throughout the cycle.

Answer 19

Oestrogen levels rise during the follicular phase and fall during luteal phase. There is a spike in the luteal phase around day 21.

Question 20

Describe the pattern of progesterone levels throughout the cycle.

Answer 20

Progesterone levels remain low during the follucular phase and begin to rise during the luteal phase. If fertilisation does not occur, the levels fall.

Question 21

Describe the pattern of LH levels throughout the cycle.

Answer 21

LH levels initially rise and then fall as oestrogen levels increase (low-moderate). Once oestrogen levels are high, a surge in LH occurs prior to day 14. Then fall.

Question 22

Describe the pattern of FSH levels throughout the cycle.

Answer 22

FSH levels are initially greater than LH during the follicular phase. As inhibin is produced, FSH levels decrease below LH and slightly rise during the LH surge.
FSH levels remain lower than LH throughout the luteal phase.

Question 23

During which stage of the ovarian cycle does the proliferative phase (uterine cycle) occur?

Answer 23

Alongside the follicular phase.

Question 24

What is the function of the proliferative phase (uterine cycle)?

Answer 24

Preparing the reproductive tract for fertilisation and implantation.
Oestrogen initiates fallopian tube formation, thickening of the endometrium, increased growth and motility of the myometrium and production of a thin alkaline cervical mucus (to facilitate sperm transport).

Question 25

During which stage of the ovarian cycle does the secretory phase (uterine cycle) occur?

Answer 25

The secretory phase runs alongside the luteal phase.

Question 26

What is the function of the secretory phase (uterine cycle)?

Answer 26

Progesterone stimulates further thickening of the endometrium into a glandular secretory form, further thickening of the myometrium, reduction of motility of the myometrium, thick acidic cervical mucus production (a hostile environment to prevent polyspermy), changes in mammary tissue and other metabolic changes.

Question 27

When does menses occur?

Answer 27

Alongside the beginning of the follicular phase.

Question 28

What triggers menses?

Answer 28

It occurs in the absence of fertilisation once the corpus luteum has broken down and the internal lining of the uterus is shed.