Lecture 7 - The Menstrual Cycle

Question 1

Is gamete production continous or periodic in males & females?

Answer 1

Continous in males (required), periodic in females

Question 2

What are the 2 cycles that occur in parallel in the menstrual cycle?

What is the average length of the menstrual cycle?

Answer 2

1) Ovarian cycle - split into follicular & luteal phase
2) Uterine cycle - split into period, proliferative & secretory phase

• 28 days but can vary from 21 to 35 days

Question 3

What are GnRH analogues/antagonists used to treat clinically?

Answer 3

1) Endometriosis - suppresses menstrual cycle and prevents cells from going through normal menstrual cycle
2) Infertility - can be caused by constant releases of GnRH, so with the analogues we can return GnRH to normal pulsatile release.

Question 4

What occurs during the early follicular phase of the ovarian cycle?

Answer 4

• Granulosa cells secrete activin, which stimulates FSH production (positive feedback).
• Little to no oestrogen production (as oestrogen in low levels inhibits FSH) .
• FSH stimulates follicle growth by increasing number of cells within growing follicle. This causes theca cells to appear, so we have enhanced aromatase function enabling follicle to produce oestrogen

Question 5

What occurs during the late follicular stage of the ovarian cycle?

Answer 5

• Dominant follicle granulosa cells produce oestrogen and inhibin
• Oestrogen initially (at low levels) exert negative feedback on FSH but increases LH receptors on granulosa cells in prep for ovulation
• Inhibin inhibits FSH

Question 6

What occurs during the ovulatory phase of the ovarian cycle (Day 14)

Answer 6

• Oestrogen rises independent of FSH (due to growth of follicle). Goes past threshold and now exerts positive feedback to cause surge in LH.
• Surge in LH triggers ovulation. Inhibin still inhibiting FSH.
• Granulosa cells start secreting progesterone (due to LH)

Question 7

What occurs during the luteal phase of the ovarian cycle?

Answer 7

• Follicle is leutinised and becomes corpus luteum.
• Corpus luteum secretes oestrogen and progesterone. Exert negative feedback on LH
• Inhibin still secreted, providing negative feedback on FSH.

Question 8

What drives proliferation of the uterus and secretion of the uterus during the uterine cycle?

Answer 8

Oestrogen drives proliferation

Progesterone + Oestrogen drives secretion

Question 9

What are the 3 layers of the uterus seen histologically?

Answer 9

1) Endometrium - split into functional layer which is shed in menstruation and basal layer which produces new functional layer.

2) Myometrium
3) Perimetrium

Question 10

What happens at the end of the menstrual cycle if fertilisation doesn’t occur?

Answer 10

Corpus luteum degrades into corpus albicans. Causes massive drop in oestrogen, progesterone & inhibin. Loss of negative feedback causes slow rise in FSH, activin is released and cycle starts again with menstruation

Question 11

What happens at the end of the menstrual cycle if fertilisation does occur?

Answer 11

Syncytiotrophoblast produced hCG which maintains corpus luteum until placenta forms where it can produce hormones and maintain pregnancy

Question 12

Give a summary of the actions of oestrogen and progesterone

Answer 12

Below