Normal Menstrual Cycle

Question 1

What marks the start and end of a menstrual cycle?

Answer 1

The length of a menstrual cycle is the number of days between the first day of menstrual bleeding of one cycle to the onset of menses of the next cycle

Question 2

What is the range for normal length of menstrual cycle?

Answer 2

Average is 28 days

but normal 21-35

Question 3

When is the menstrual cycle most likely to be irregular?

Answer 3

The extremes of reproductive life (menarche and menopause) due to anovulation and inadequate follicular development

Question 4

What are the three events that occur in the ovaries during the menstrual cycle?

(the three phases of the menstrual cycle)

Answer 4

1. Follicular phase
2. Ovulation
3. Luteal phase

Question 5

What phase of the menstrual cycle is constant?

Which phase of the menstrual cycle is cycle length variability most likely to derive from?

Answer 5

The luteal phase is always 14 days

The variability of cycle length is usually derived from varying lengths of follicular phase which can range from 10-16 days

Question 6

What physiological axis controls menstruation?

Answer 6

The hypothalamic-pituitary-gonadal (HPG) axis

Question 7

What hormones control the ovaries?

Answer 7

GnRH is released in a pulsatile fashion from the hypothalamus

which stimulates the anterior pituitary to release LH and FSH

which act on the ovaries

Question 8

What are the two types of cells in the follicle which are involved in oestrogen and progesterone synthesis?

What hormones do they respond to?

Answer 8

Theca cells…respond to LH

Granulosa cells…respond to FSH

Question 9

What hormone is released after ovulation occurs and is used as a marker of fertility?

Answer 9

Progesterone

Question 10

Which change marks the transformation of the primordial follicle into a primary follicle?

Answer 10

Development of the zona pellucida

Question 11

What is the role of the granulosa cells in the follicle?

Answer 11

Granulosa cells in follicles produce oestradiol (oestrogen)

When the follicle becomes the corpeus luteum, granulosa luetin cells produce progesterone which facilitates implantation

Question 12

Describe the levels of hormones expected at the start of the follicular phase

Answer 12

• At the start of menses there is little ovarian hormone production and the follicle begins to develop independently of gonadotropins or ovarian steroids
• Due to low steroid and inhibin levels there is little negative feedback at the HPG axis resulting in an increase in FSH and LH levels which stimulate follicle growth and oestrogen production

Question 13

During the follicular phase oestrogen levels start to increase.

What are the effects of this?

Answer 13

As oestrogen levels rise, negative feedback reduces FSH levels and only one follicle can survive to ovulation

Follicular oestrogen eventually becomes high enough to stimulate the LH surge

Question 14

Describe and explain the LH surge

Answer 14

Mid-late follicular stage the follicular oestrogen levels are high enough to initiate positive feedback at the HPG axis increasing GnRH

The effect is only reflected in LH levels (the LH surge) due to increased follicular inhibin which selectively inhibits FSH production at the anterior pituitary

Granulosa cells become luteinised and express receptors for LH

Question 15

What occurs due to the LH surge?

Answer 15

The follicle ruptures and the mature oocyte is assisted to the fallopian tube by fimbria

Question 16

What happens to the follicle after ovulation?

Answer 16

Following ovulation the follicle remains luteineised, secreting oestrogen and now also progesterone, reverting back to negative feedback on the HPG axis.

This together with inhibin (inhibits FSH) stalls the cycle in anticipation of fertilisation

Question 17

What is the corpus luteum? What does it do?

Answer 17

The corpus luteum is the tissue in the ovary that forms at the site of a ruptured follicle following ovulation

It produces:

• oestrogens
• progesterone
• inhibin

to maintain conditions for fertilisation and implantation

Question 18

In the absence of fertilisation, what happens to the corpus luteum?

Answer 18

it spontaneously regresses after 14 days

There is a significant fall in hormones, relieving negative feedback, resetting the HPG axis ready to begin the cycle again

Question 19

What are the phases of the uterine cycle?

Answer 19

Proliferative phase

Secretory phase

Menses

Question 20

Discuss the proliferative phase

Answer 20

• the proliferative phase runs alongside the follicular phase
• prepares the reproductive tract for fertilisation and implantation
• oestrogen initiates:
  
  • fallopian tube formation,
  • thickening of the endometrium
  • increased growth and motility of the myometrium
  • production of a thin alkaline cervical mucus (to facilitate sperm transport)

Question 21

Discuss the secretory phase of the uterine cycle

Answer 21

• the secretory phase runs alongside the luteul phase
• progesterone stimulates:
  
  1. further thickening of the endometrium into a glandular secretory form,
  2. thickening of the myometrium,
  3. reduction of motility of the myometrium,
  4. thick acidic cervical mucus production (a hostile environment to prevent polyspermy)
  5. changes in mammary tissue and other metabolic changes

Question 22

Discuss menses of the uterine cycle

Answer 22

Menses marks the beginning of a new menstrual cycle

• it occurs in the absence of fertilisation
• occurs once the corupus luteum has broken down
• menstrual bleeding usually lasts between 2-7 days