Menstrual Cycle

Question 1

State what is happening at the start of cycle

Answer 1

• 1st day of menstruation
• Endometrium loses trophic hormone support - loss of ovarian hormone support
• FSH levels stimulate early development of follicles
• Low steroid and inhibin levels
• Little inhibition at the hypothalamus or anterior pituitary
• FSH levels rising stimulates further follicle development

Question 2

What does FSH do to follicles

Answer 2

• FSH binds to granulosa cells
• Follicular development continues
• Theca interna appears
• Follicle now capable of oestrogen secretion from granulosa cells and theca cells
  - Theca cells produce androgens which go to granulosa cells to produce oestrogen
  - Oestrogen secretion upregulates FSH receptors on granulosa cells to further increase oestrogen levels
• Inhibin secretion begins from granulosa cells

Question 3

Describe the mid-follicular phase

Answer 3

• Dominant follicle produced along with second polar body
• Prevent recruitment of further follicles
• Follicular oestrogen exerts positive feedback at the hypothalamus and anterior pituitary
• Gonadotrophin levels rise - especially LH
• Follicular inhibin rising - selective inhibition on FSH production
  
  • FSH low to prevent development of other follicles

Question 4

What happens just before ovulation

Answer 4

• Circulating oestrogen and inhibin rise rapidly
• Oestrogen production no longer dependent on FSH
• Surge in LH production
• Progesterone production begins
  
  • Granulosa cells become responsive to LH - express receptors for LH
• Modulation of GnRH pulsatile release

Question 5

What happens just after ovulation

Answer 5

• After ovulation, follicle is luteinised
• Secretes oestrogen and progesterone in large quantities
  Inhibin continues to be produced
• LH is now suppressed because of negative feedback from progesterone
  
  • Oestrogen in presence of progesterone has negative feedback on LH
• Further gamete development suspended - waiting phase established

Question 6

Explain the luteal phase

Answer 6

• Corpus luteum - preprogramed life span of ~14 days
• Produces progesterone and oestrogen from androgens
• Produces inhibin
• Promotes production of progesterone
• Regressed spontaneously in the absence of a further rise in LH

Question 7

What happens if no fertilisation happens

Answer 7

• In the absence of further rise in LH, corpus luteum regressed
• Dramatic fall in gonadal hormones
• Relieving negative feedback

Question 8

What happens if there is fertilisation

Answer 8

• Syncytiotrophoblast produces human chorionic gonadotrophin
  
  • hCG functions as LH and makes the embryo presence known

Question 9

What is the normal menstrual cycle duration

Answer 9

• Normal duration 21-35 days
• Variations in cycle duration due to variation in the length of follicular phase
  
  • Luteal phase strictly controlled - 14±2 days

Question 10

What are the stages of ovarian cycle

Answer 10

• Follicular phase - FSH stimulates the development of the follicle
• After the LH surge, ovulation occurs where follicle ruptures ovary lining
• Luteal phase - corpus luteum

Question 11

Describe the stages of uterine cycle

Answer 11

• Lining of the uterus (endometrium) is responsive to hormones produced by the ovary
• Proliferative phase - responds to oestrogen by proliferating
  
  • Oestrogen is a trophic hormone - cause cells to divide
    Secretory phase - responds to oestrogen and progesterone by secreting

Question 12

Describe the structure of the uterine wall

Answer 12

• M = myometrium - muscular wall
  
  • Thickens and changes contractility but does not shed
• E = endometrium - epithelial lining
  
  • Functional layer (F) is hormone responsive and is shed if no pregnancy occurs
    -
    Grows/thickens in menstrual cycle
    
    • Secretory
  • Basal layer (B) is stem cell layer which provides source from which a new functional layer is developed

Question 13

Explain the changes to the uterine wall at the different stages of the uterine cycle

Answer 13

• Early proliferative - glands sparse, straight
• Late proliferative - functional layer has doubled, glands now coiled
• Early secretory - endometrium max thickness, very pronounced coiled glands
• Late secretory - glands adopt characteristic ‘saw tooth’ appearance

Question 14

What is the role of inhibin in the control of ovulation

Answer 14

• Inhibin reduces the release of FSH from the anterior pituitary
• Released by granulosa cell

Question 15

Outline the role of oestrogen in the control of ovulation

Answer 15

• Oestrogen has a negative and positive feedback loop to the hypothalamus and anterior pituitary
• At moderate levels of oestrogen (before ovulation), positive feedback initiated causing high LH and FSH
• Oestrogen in the presence of progesterone causes negative feedback and reduces LH
• Released by granulosa cell

Question 16

What factors affect menstrual cycle

Answer 16

• Physiological factors - pregnancy, lactation (suppressed HPO axis)
• Emotional stress
• Low body weight

Question 17

Explain the importance of pulsatile GnRH release

Answer 17

• Intermittent GnRH receptor required for fertility
• If GnRH receptors are exposed to continuous presence of GnRH, they become desensitized
  
  • FSH and LH production stops
  • Gonadal steroid production stops

Question 18

Explain the use of GnRH agonists as treatment

Answer 18

• Endometriosis - plaques of endometrium growing in areas other than the uterus
  
  • Has sex hormones which can irritate peritoneum
  • Treatment with GnRH agonist to relieve symptoms
• GnRH agonist forces GnRH receptors to become desensitized
  
  • Therefore FSH and LH levels will decrease and steroid hormone levels will decrease
  • Used to treat fibroids, endometriosis
• GnRH agonist should not be used long term as can have menopause effect
  
  • Oestrogen needed for maintaining bone density

Question 19

Explain the actions of oestrogen in a nonpregnant woman

Answer 19

• Fallopian tube function
• Thickening of endometrium - most important
• Growth and motility of myometrium - promote motility of fallopian tube
• Thin alkaline cervical mucus
• Vaginal changes
• Changes in skin, hair, metabolism

Question 20

Explain the actions of progesterone in a nonpregnant woman

Answer 20

• Further thickening of endometrium into secretory form
• Thickening of myometrium, but reduction of motility
• Thick acidic cervical mucus - physical barrier for entry into female reproductive tract
  
  • Reduce infection chance
• Changes in mammary tissue
• Increased body temperature
• Metabolic changes
• Electrolyte changes