7 The Menstrual Cycle

Question 1

Between what range does a typical menstrual cycle last?

Answer 1

21-35 days

Question 2

Name the 2 cycles involved in the menstrual cycle and what the function of each cycle is.

Answer 2

Ovarian cycle:

Provide envrionment for oogenesis to occur and production of steroid hormones

Uterine cycle:

Prepare uterus to receive fertilised oocyte

Question 3

Describe the male HPG axis:

Answer 3

Question 4

Why is it so important that GnRH is released in a pulsatile nature?

Answer 4

Key in fertility

Receptors can become desensitised if over-exposed to hormone

Question 5

What is endometriosis? How can it be treated?

Answer 5

Ectopic endometrial tissue can develop- leads to significant pain

Patient given continuous GnRH- switch HPG axis off

Continuous exposure to GnRH means receptors become desensitised

Question 6

Continuous GnRH can be given to patients with endometriosis. Who else might it be given to?

Answer 6

Patients suffering from precocious puberty- temporarily halts axis

Question 7

What are the roles of FSH and LH in females?

Answer 7

FSH:

• Stimulate follicles in ovary to develop
• Follicles produce oestrogen and inhibin

LH:

• Responsible for ovulation

Question 8

The ovarian cycle can be divided into 2 phases. What are these 2 phases?

Answer 8

1. Follicular phase
   
   1. Preparing follicule for ovulation
2. Luteal phase
   
   1. Follicle after ovulation- wait to see if fertilsation/implantation occurs

Question 9

Explain what’s happening at numbers 1-5 in the follicular phase of the ovarian cycle:

Answer 9

1. Few small follicles developing, granulosa cell number increase, theca cells develop, triggers oestrogen production
2. Oestrogen still at low enough levels to have negative feedback on hypothalamus and pituitary
3. Graafian follicle has developed- still releasing oestrogen, oestrogen levels high- have positive feedback on LH release
4. LH rises- due to high oestrogen levels
5. LH rises (much higher than FSH as inhibin released which inhibits FSH)

Question 10

Explain what happens in the luteal phase of the ovarian cycle.

Answer 10

Corpus luteum- 14 day lifespan (always)

1. Corpus luteum secreting oestrogen and progesterone (and inhibin)
2. Progesterone promotes negative feedback of oestrogen on hypothalamus and anterior pituitary
3. After 14 days oestrogen, progesterone and inhibin have dropped- cycle starts again

Question 11

What are the 2 phases which the uterine cycle can be divided into?

Answer 11

(Menstrual phase)

1. Proliferative phase
2. Secretory phase

Question 12

What layers make up the wall of the uterus?

Answer 12

• Myometrium: muscular wall
• Endometrium: epithelial layer
  
  • Functional layer
    
    • Shed during menstruation
  • Basal layer
    
    • Allows regrowth at start of new cycle

Question 13

What happens in the proliferative phase of the uterine cycle?

Answer 13

1. Oestrogen from ovary causes endometrium proliferate and thicken (after menses)
2. Simple, straight glands in endometrium coil- functional layer doubles in thickness

Question 14

What happens in the secretory phase of the uterine cycle? (if implantation doesn’t occur)

Answer 14

1. Coiled glands produced in proliferative stage- become secretory due to progesterone
2. Eventually glands lose structure, endometrium ready to shed -if implantation doesn’t occur

Question 15

What happens in the menstrual cycle if implantation occurs?

Answer 15

1. Embryonic tissue (trophoblast produces hCG)
2. hCG acts as gonadtrophin- same function as LH
3. hCG maintains corpus luteum- producing oestrogen and prgesterone

Question 16

List the functions of the steroid hormones oestrogen and progesterone.

(aka ovarian steroids)

(LH and FSH= gonadotrophins)

Answer 16