Menstrual Cycle and Hormonal Control

Question 1

What are the 3 physiological systems that regulate the menstrual cycle?

Answer 1

• hypothalamic-pituitary-ovarian axis
• ovarian cycle (events in ovary: follicular, ovulation, luteal)
• endometrial cycle (events in endometrium: menstrual, proliferative, secretory)

Question 2

Define menarche

Answer 2

• end of puberty
• marks beginning of potential fertility
• stimulated by maturation of GnRH pulsatility so primarily hypothalamic

Question 3

Define menopause

Answer 3

• marks end of natural fertility

- exhaustion of primordial follicles so primarily ovarian

Question 4

What is premature ovarian failure (POF)?

Answer 4

• menopause occuring in women under 40
• can be idiopathic, autoimmune disorder, genetic disorder
• symptoms can be treated with oestrogen replacement

Question 5

Describe how gonadotropin levels change throughout female life

Answer 5

• LH and FSH peak during foetal life and again at early infancy
• falls and stays at low levels throughout childhod
• at onset of puberty, rise slowly and will oscillate at regular monthly intervals
• at menopause, due to depletion of follicles and therefore absence of negative feedback, levels rise to very high levels

Question 6

What is the role of sex steroids on gonadotropins and how does this change throughout life?

Answer 6

• they suppress gonadotropin output in a negative feedback mechanism
• in childhood, the levels are sufficient to do so
• as you get older, higher levels of sex steroids are needed to suppress release as the gonadotropins get less sensitive to it

Question 7

What releases gonadotrophin releasing hormone?

Answer 7

small body neurons in arcuate nucleus and the preoptic area of the hypothalamus into hypophyseal circulation to bind to receptors in the anterior pituitary

Question 8

What is the function of the gonadotropin releasing hormone?

Answer 8

stimulates release of FSH and LH from anterior pituitary

Question 9

Describe the menstrual cycle

Answer 9

• day 1-7: multiple follicles develop, by day 7 one becomes dominant (will be the one that will release the egg)
• day 7-14: dominant follicle develops
• day 14: ovulation
• day 14-25: corpus luteum develops and carries out function
• day 25-28: corpus luteum degenerates

Question 10

Describe how the levels of FSH and LH change during the menstrual cycle

Answer 10

• FSH: increases in early follicular phase, then decreases for rest of cycle except small mid-cycle peak
• LH: constant most of follicular phase, then large mid-cycle peak just before ovulation, then rapid decrease and further slow decline throughout luteal phase

Question 11

Describe how oestradiol and progesterone levels change during the menstrual cycle

Answer 11

• oestradiol: low and stable for first week and then increases rapidly in second week, declines before the LH peak, second increase in last few days of cycle due to corpus luteum
• progesterone: low levels in follicular phase due to ovary release, small increase just before ovulation, then large increase due to corpus luteum formation

Question 12

Describe how inhibin levels change during the menstrual cycle

Answer 12

increases in late follicular phase, remains high during luteal phase, decreases as corpus luteum degenerates

Question 13

Describe the feedback process of ovarian steroids

Answer 13

• most of cycle has a negative feedback on the pituitary and hypothalamus which reduces LH and FSH production
• positive feedback occurs near ovulation:
• oestradiol levels gradually increased after reaching a certain threshold for 2 days
• HP axis reverses its sensitivity to oestrogens
• increases sensitivity of anterior pituitary to GnRH causes LH surge

Question 14

What are the roles of oestradiol?

Answer 14

• prepare femal repro tract for fertilisation and implantation
• induces expression of progesterone receptors in target tissues
• tubular epithelium (stimulates proliferation of epithelial lining and secretion of fluid)
• stimulates hyperplasia and hypertrophy of epithelial lining
• up-regulates receptors for prostaglandins and oxytocin, and increases spontaneous activity on smooth muscle
• increases mucus volume and decreases viscosity in the cervix

Question 15

What are the roles of progesterone?

Answer 15

• prepares female repro tract for fertilisation and implantation
• reduces proliferation of epithelial lining and reduces secretion of fluid of tubular epithelium
• stimulates secretory phase of menstrual cycle and further growth and secretion from glands
• reduces sensitivity to oxytocin and down-regulates receptors, and relaxes smooth muscle in repro tract
• reduces mucus volume and increases viscosity in cervix

Question 16

metrorrhagia

Answer 16

irregular bleeding

Question 17

What causes dysmenorrhea?

Answer 17

• overproduction of prostaglandins by the endometrium in response to decreased plasma oestrogen and progesterone
• leading to excessive uterine contractions
• prostaglandins can affect the smooth muscle elsewhere as well which is why people can experience nausea, vomiting, headache etc as well

Question 18

What can be the cause of PMS?

Answer 18

falling progesterone levels at end of cycle (progesterone - anxiolytic effect)

Question 19

What are the causes of amenorrhoea?

Answer 19

• primary:
• anatomical/congenital abnormality
• genetic (Turner’s Syndrome)
• secondary:
• precnancy
• lactation
• exercise/nutrition
• menopause
• PCOS
• iatrogenic

Question 20

What are the symptoms of amenorrhoea?

Answer 20

• oestrogen deficiency (hot flushes, vaginal dryness)

- loss of bone mineralisation (reduction in peak bone mass, osteopenia/osteoporosis)

Question 21

What are the therapeutic uses of GnRH?

Answer 21

• endometriosis: continuous administration of GnRH inhibits gonadotropin secretion and reduces oestrogen levels leading to reduced endometriotic tissue
• IVF: used before controlled IVF cycle

Question 22

What are the different types of birth control pill?

Answer 22

• fixed combination (dosage of oestrogen and progestin the same)
• varying-dose (2 or 3 different dosages of oestrogen and progestin)
• progestin-only pi;;

Question 23

How do birth control pills work?

Answer 23

• contraceptive steroids feedback on hypothalamic neurons and gonadotropin cells to suppress LH and FSH secretion
• so no follicular development or LH surge
• progestin effect causes cervical mucus thickening and increases viscosity
• reduces uterus and oviduct motility as well as endometrial changes
• inhibits sperm penetration and chances of implantation