1: Menstruation: Physiology of the menstrual cycle

Question 1

When does menarche start

Answer 1

11-15 years

Question 2

When does menopause occur

Answer 2

45-55 years

Question 3

Explain hormone secretion to control the menstrual cycle

Answer 3

GnRH is released from the hypothalamus and stimulates LH and FSH release from anterior pituitary gland.
LH - acts on theca cells
FSH - acts on granulosa cells

Question 4

What is the role of LH

Answer 4

LH binds to theca cells and stimulates androgen production

Question 5

What is the role of FSH

Answer 5

FSH binds to granulosa cells: increase conversion of androgens to oestrogen. Enables inhibin secretion

Question 6

What is the role of oestrogen in negative feedback

Answer 6

Moderate oestrogen - negative feedback

High oestrogen - positive feedback

Question 7

What is the role of inhibin

Answer 7

Inhibits FSH

Question 8

What are the 3 phases of the ‘ovarian’ menstrual cycle

Answer 8

1. Follicular Phase
2. Ovulation
3. Luteal Phase

Question 9

Which part of the menstrual cycle varies

Answer 9

Follicular Phase - varies in length

Question 10

Explain follicular phase

Answer 10

• Initially follicles can grow steroid independent
• As the follicles grow they produce more oestrogen and progesterone
• This causes negative inhibition of LH and FSH
• Only the follicle with most FSH receptors will survive and continue to grow (this is called the dominant follicle)
• The dominant follicle when growing will produce more oestrogen and inhibin. High levels of oestrogen causes a switch to positive feedback causing a LH surge

Question 11

What day is ovulation normally

Answer 11

14d

Question 12

Explain ovulation

Answer 12

• LH Surge causes release of oocyte from the follicle
• Oocyte is available for 24h to be fertilised
• Follicle releases oestrogen and progesterone which causes negative feedback on HPA axis preparing for fertilisation

Question 13

How long is the luteal phase

Answer 13

14d

Question 14

Explain the luteal phase

Answer 14

• The corpus luteum forms at the site of the ruptured follicle
• Corpus luteum releases oestrogen and progesterone
• This negatively feedback on HPA axis
• The corpus luteum has a lifespan of 14-days
• When the corpus luteum dies oestrogen and progesterone decreases re-setting the axis

Question 15

Explain what happens if pregnant

Answer 15

• Syncytiotrophoblasts release bHCG which maintains the corpus luteum
• At 4m the placenta can produce enough steroids to maintain the HPG axis

Question 16

What are the three phases of the ‘ovarian’ cycle

Answer 16

1. Follicular
2. Ovulation
3. Proliferative

Question 17

What are the two phases of the ‘uterine cycle’

Answer 17

1. Proliferative

2. Secretory

Question 18

Explain proliferative phase of uterine cycle

Answer 18

Oestrogen causes endometrial proliferation, opening fallopian tube, thinning and alkaline cervical mucus plug to aid sperm transport

Question 19

Explain secretory phase

Answer 19

Progesterone causes glandular secretory endometrium. And produces a thick acidic cervical mucus plug = preventing sperm entering

Question 20

What is the proliferative phase equivalent of the ovarian cycle

Answer 20

Follicular phase

Question 21

What is the secretory phase equivalent of the ovarian cycle

Answer 21

Luteal phase

Question 22

What is the menopause

Answer 22

End of women’s reproductive life

Question 23

When does the menopause start

Answer 23

Perimenopause at 45-years

Question 24

What is the average age of the menopause

Answer 24

51-years

Question 25

What defines menopause

Answer 25

Amenorrhoea for 12-months

Question 26

Explain hormonal changes in oestrogen

Answer 26

• There is decrease sensitivity of follicles (ovaries) to LH and FSH
• This means there is no follicle growth and low concentration of oestrogen - causing anovulatory cycles
• As oestrogen is low, negative feedback is removed causing a rise in LH and FSH

Question 27

What are 3 symptoms of peri menopause

Answer 27

UTI
Vaginal bleeding
Hot flushes

Question 28

What causes irregular bleeding in the peri menopause

Answer 28

As there is oestrogen which causes proliferation of the endometrium, however there is no progesterone, which means the endometrium breaks down

Question 29

What causes oestrogen breakthrough bleeding

Answer 29

Progesterone is required to stabilise the endometrium. With anovulatory cycles no corpus luteum is formed and no progesterone released. This means as there is a gradual decrease in oestrogen the endometrium degrades causing gradual bleeding