Menstrual Cycle

Question 1

What controls the menstrual cycle?

Answer 1

HPG axis

Hypothalamic-pituitary-gonadal axis

Question 2

Describe the HPG axis

Answer 2

Hypothalamus - produces GnRH (gonadotrophin releasing hormone) - acts on anterior pituitary

Anterior pituitary - produces FSH (follicle stimulating hormone) and LH (luteinising hormone) - act on ovary

FSH - acts on granulosa cells - produce inhibin and oestrogen

LH - acts on theca cells - produce androgens

Question 3

What are the 2 different cycles that make up the menstrual cycle?

Answer 3

Ovarian cycle

Uterine cycle

Question 4

What are the phases of the ovarian cycle?

Answer 4

Follicular phase

Luteal phase

Question 5

What happens in the follicular phase?

Answer 5

FSH rises -> stimulates follicle growth
First mature follicle produces oestrogen
Oestrogen inhibits other follicle growth
Oestrogen reaches peak = LH surge (~day12)
Increased LH = follicle membrane thins
24-48hrs post surge - follicle ruptures = ovulation

Question 6

What is the first mature follicle also known as?

Answer 6

Graafian follicle

Question 7

What are the effects of oestrogen?

Answer 7

Endometrial thickening
Cervical mucus thinning
Inhibition of LH production

Question 8

What happens in the luteal phase?

Answer 8

LH + FSH -> stimulate follicle to change to corpus luteum
Corpus luteum produces progesterone
No pregnancy = fall in LH + FSH -> degeneration of corpus luteum
Loss of corpus luteum -> fall in progesterone -> menstruation

Question 9

What are the effects of progesterone?

Answer 9

Endometrium becomes receptive to implantation
Increased body temp

Negative feedback -> fall in LH + FSH

Question 10

What are the phases of the uterine cycle?

Answer 10

Proliferative phase
Secretory phase
Menses

Question 11

What happens in the proliferative phase?

Answer 11

Rise in oestrogen levels

Repair + growth of functional endometrial layer

• increased thickness
• increased vascularity
• increased no. of secretory glands

Question 12

What happens in the secretory phase?

Answer 12

Increased progesterone level

• thickening of endometrium
• thickening of myometrium
• thick acidic mucus

Question 13

What happens during menses?

Answer 13

Corpus luteum degenerates -> fall in progesterone
Spiral arteries in endometrium contract
Loss of blood supply = endometrium becomes ischaemic
Shedding of functional endometrial layer