The Menstrual Cycle and its Hormonal Control

Question 1

3 physiological systems that regulate the female reproductive (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

Length of menstrual cycle

Answer 2

mean 28 days (+/- 3.95) for about 40 years

Question 3

MENARCHE

Answer 3

end of puberty and marks beginning of potential fertility

– maturation of GnRH pulsatility so primarily hypothalamic

Question 4

MENOPAUSE

Answer 4

• occurs around 45 - 55 yrs (average 51 yrs ) and marks end of
  natural fertility
  – “Exhaustion” of primordial follicles so primarily ovarian
  – Premature Ovarian Failure (POF)

Question 5

early menopause

Answer 5

• Menopause can occur in women under the age of 40 (idiopathic, autoimmune disorders, genetic disorders such as Fragile X, chemotherapy, radiation)
• Symptoms can be treated with oestrogen replacement (hormone replacement therapy – HRT)

Question 6

Gonadotrophin releasing hormone

Answer 6

secreted by small body neurons in arcuate nucleus & preoptic area of hypothalamus

Question 7

where is GnRH secreted into

Answer 7

Secreted into median eminence and hypophyseal portal system

Question 8

what is the function of GnRH

Answer 8

• GnRH binds to receptors on gonadotophic cells of the anterior pituitary
• Leads to release of follicule-stimulating hormone (FSH) and luteinising hormone (L

Question 9

Hypothalamic-pituitary- ovarian axis

Answer 9

• GnRH neurons release GnRH in rhythmic pulses (about 1/hr)

* GnRH half-life in blood 2-4mins

Question 10

What cells do LH act on

Answer 10

theca cells which produce androgens and progestins

Question 11

What cells do FSH act on

Answer 11

Granuloma cells (these also have LH receptors) which produce inhibins activins and oestrogen’s

Question 12

Theca cells

Answer 12

Superficial layer of follicle
• Have LH receptors
• Convert cholesterol into pregnenolone
• Then produce androstenedione and testosterone

Question 13

Granulosa cells

Answer 13

• Deep compared to theca
• Layer increases in size markedly during 1°
to 2° follicle development
• Have LH and FSH receptors
• Also convert cholesterol into pregnenolone + activate aromatase

Question 14

• Oestrogens & • Positive feedback occurs near ovulation (end of follicular phase)

Answer 14

– Most of cycle have negative feedback on pituitary and hypothalamus
– Reduce LH and FSH production

Question 15

• Positive feedback occurs near ovulation (end of follicular phase)

Answer 15

– Oestradiol levels gradually increase after reached a certain threshold for a min of 2 days,
HP axis reverses its sensitivity to oestrogens
– Leads to oestrogen positive feedback
– Increased sensitivity of anterior pituitary to GnRH leads to LH surge

Question 16

Roles of Oestradiol in tubal epithelium

Answer 16

– Stimulates proliferation of epithelial lining

– Secretes sugar-rich fluid

Question 17

Roles of Oestradiol in endometrium

Answer 17

– Stimulates hyperplasia and hypertrophy of epithelial lining
– Glands elongate and spiral arteries grow

Question 18

Roles of Oestradiol in smooth muscle

Answer 18

– Up regulates receptors for prostaglandins and oxytocin

– Spontaneous activity increased

Question 19

Roles of Oestradiol in cervix

Answer 19

– Increases mucous volume

– Decreases mucous viscosity

Question 20

Roles of Oestradiol - Induces expression of progesterone receptors in target tissues

Answer 20

required for corpus luteum to work

Question 21

Roles of Oestradiol

Answer 21

• Prepare female reproductive tract for fertilisation and implantation

Question 22

Roles of Progesterone in tubual epithelium

Answer 22

– Reduced proliferation of epithelial lining

– Reduces secretion of sugar-rich fluid

Question 23

Roles of Progesterone in endometrium

Answer 23

– Stimulates secretory phase menstrual cycle

– Stimulates further growth and secretion from glands

Question 24

Roles of Progesterone in esmooth muscle

Answer 24

– Reduces sensitivity to oxytocin by down regulating receptors
– Brings about relaxation of smooth muscle in reproductive tract and elsewhere

Question 25

Roles of Progesterone in cervix

Answer 25

– Reduces mucous volume and increases its viscosity

Question 26

Dysmenorrhoea - Painful Periods

Answer 26

• Menstrual cramps
• Main cause is overproduction of prostaglandins by endometrium in response to decreased plasma oestrogen and progesterone
• Leads to excessive uterine contractions

Question 27

systemic symptoms

Answer 27

• Prostaglandins can affect smooth muscle elsewhere and may account form some of the systemic symptoms that sometimes accompany cramps e.g. nausea, vomiting, headache

Question 28

Premenstrual Syndrome (PMS)

Answer 28

Progesterone has anxiolytic (anti-anxiety) effect. Therefore may be due to falling progesterone levels at the end of the cycle

Question 29

Amenorrhoea - No Periods

Answer 29

• Primary
– Anatomical/ congenital abnormality (underdevelopment or absence of
uterus/vagina)
– Genetic (Turner’s syndrome)
• Secondary
– Pregnancy
– Lactation
– Exercise/Nutrition
– Menopause
– Polycystic Ovarian Syndrome
– Iatrogenic (surgery,  medication)

Question 30

• Symptoms of PMS

Answer 30

– Oestrogen deficiency (Hot flushes (flashes), Vaginal dryness)
– Loss of bone mineralisation (Reduction in peak bone mass attained, Osteopenia/ osteoporosis)

Question 31

Therapeutic uses of GnRH

Answer 31

• Pulsatile release of GnRH stimulates FSH and LH secretion
• Continuous administration of GnRH causes suppression of gonadotropin
secretion

Question 32

• Endometriosis

Answer 32

– Common condition with growth of endometrial tissue outside the uterine cavity
– Tissue responds to oestrogens of menstrual cycle
• results in pain and infertility
– Treatment?
– Continuous administration of GnRH analogue inhibits gonadotropin secretion and
reducing oestrogen levels, leading to reduced endometriotic tissue

Question 33

• IVF

Answer 33

– GnRH analogues used before controlled IVF cycle commences

Question 34

Birth Control Pill

Answer 34

• Fixed combination OCP
– Dosage of oestrogen and progestin is the same
• Varying-dose OCP
– 2 or 3 different dosages of oestrogen and progestin
• Progestin-only (“minipill”) OCP

Question 35

how does brith control pill work

Answer 35

• Contraceptive steroids feedback on hypothalamic neurons and gonadotropin cells and suppress LH and FSH secretion
– So no follicular development or LH surge (ovulation)
• Progestin effect causes cervical mucous thickening and increase viscosity,
reduces uterus and oviduct motility, endometrial changes
– Inhibits sperm penetration
– Reduces chances of implantation