The Menstrual Cycle

Question 1

What is the average length of the menstrual cycle?

What are the 2 parts of the cycle?

Answer 1

28 days (Varies from 21-35 days due to variation in follicular phase)

Ovarian and Uterine cycles

Question 2

Does Oestrogen/ Progesterone exhibit negative or positive feedback on the HPG axis?

Answer 2

Can be either depending on phase of cycle

Question 3

Name the phases of the Ovarian and Uterine cycles Pre and Post Ovulation

Answer 3

Ovarian;

• Pre: Follicular phase (Prepares a follicle for ovulation)
• Post: Luteal phase

Uterine;

• Pre: Period/ Menstrual, then Proliferative phase
• Post: Secretory phase

Question 4

What are 2 occasions we can give GnRH to patients continuously (Not in a pulsatile fashion)

Answer 4

• To switch off axis in Endometriosis (can cause a lot of pain)
• To temporarily halt axis in Precocious Puberty

Question 5

What does FSH do?

Answer 5

Acts at ovary to allow follicles to develop at start of menstrual cycle

(Follicles also produce Inhibin to prevent other follicles developing, via negative feedback)

Question 6

What does LH do?

Answer 6

Responsible for ovulation (LH Surge)

Question 7

Outline the Early Follicular Phase (Days 0-5)

Ovarian cycle, Pre Ov

Answer 7

• Granulosa cells secrete Activin, acting on AP Gland to increase FSH Production and number of FSH Receptors on Granulosa cells
• Number of Granulosa cells increase and cause development of Theca cells
• Oestrogen is produced from Granulosa and Theca Cells, at LOW levels. (Exerts -ve feedback on HT and AP Gland)
• Follicle continues to grow under FSH influence

Question 8

Outline the Late Follicular Phase (Days 5-14)

Ovarian cycle, Pre Ov

Answer 8

As follicle develops into Graafian Follicle and Oestrogen levels rise;

• Oestrogen increases number of FSH receptors on follicle LH receptors on Granulosa cells
• Oestrogen exerts +ve feedback on HT and AP to increase LH levels
• Inhibin produced to prevent more than 1 follicle being stimulated by FSH (Also enhances Androgens to Oestrogen conversion)
• LH Levels rise to be higher than FSH Levels

Question 9

Which enzyme in the Granulosa cells convert Androgens to Oestrogen?

Answer 9

Aromatase (Androgens made in Theca cells)

Question 10

In the Ovulatory Phase (Day 14) of the Ovarian cycle, Oestrogen continues to rise.

How do LH, FSH and Progesterone levels rise?

Answer 10

High Oestrogen levels-> +ve feedback on HT and AT

• This causes an LH Surge
• No rise in FSH due to continued Inihibin production from Granulosa cells
• Due to LH, Granulosa cells start secreting Progesterone at low levels

Question 11

Outline the Luteal Phase

Ovarian cycle, Post Ov

Answer 11

• Granulosa and Theca cells become Corpus Luteum, which produces Oestrogen, Progesterone and Inhibin
• Presence of Progesterone causes Oestrogen to exert -ve feedback on HT and AT
• LH levels decrease and FSH levels stay low

Question 12

The Luteal Phase is essentially the ‘Waiting Phase’ to see if oocyte fertilises and implants or not.

What happens to Oestreogen, Progesterone, Inhibin and FSH levels if no implantation occurs?

Answer 12

• O,P,I decrease, allowing cycle to re-start
• Loss of -ve feedback-> Slight FSH increase

(Also Corpus Luteum becomes Corpus Albicans)

Question 13

Identify the main hormones in the Proliferative and Secretory Phases of the Uterine Cycle

Answer 13

Proliferative: Oestrogen

Secretory: Progesterone (Oestreogen also present)

Question 14

The Ovarian and Uterine cycles occur in parallel

Briefly, what happens in the Ovarian and Uterine cycles?

Answer 14

Ovarian;

• Production of steroid hormones
• Preparation of ovary to provide an environment for Oogenesis to occur

Uterine;
- Preparation of uterus to receive a fertilised oocyte

Question 15

The uterus is made of 3 layers, Endometrium, Myometrium and Perimetrium

Compare the subdivisions of the Endometrium

Answer 15

Functional Layer: Sheds during menstruation, responsive to hormones

Basal Layer: Develops into new functional layer at start of a new cycle

Question 16

Describe the Early and Late Proliferative Phase of the Uterine Cycle (Pre Ov)

Answer 16

Early;

• Endometrium will proliferate and thicken in response to Oestrogen
• Endometrium contains sparse, straight glands

Late;

• Functional layer thickens (doubles)
• Glands become coiled

Question 17

Outline the Secretory Phase

Uterine cycle, Post Ov

Answer 17

• Glands become secretory under influence of Progesterone, Arterioles coil
• Towards end of phase, glands lose their structure and endometrium becomes ready to shed its functional layer if implantation has not occurred

Question 18

What arteries supply the Basal and Functional layer of Endometrium?

Answer 18

Basal- Straight

Functional- Spiral

Question 19

What happens to Corpus Luteum if fertilisation occurs?

Answer 19

• Synctiotrophpblast (of zygote) produces Beta-hCG
• This hormone acts as LH, maintaining Corpus Luteum
• CL continues to produce Progesterone, Oestrogen and Inhibin until Placenta is formed

Question 20

List 4 functions of Oestrogen on the Reproductive Tract to promote fertilisation

Answer 20

• Endometrium proliferation
• Myometrium proliferation
• Increased motility of Fallopian Tube
• Thin, alkaline cervical mucus production

Question 21

List 3 functions of Progesterone on the Reproductive Tract to Sustain a Viable Pregnancy

Answer 21

• Secretory function of endometrium increased
• Thickening and reduced motility of Myometrium
• Thick, acid cervical mucus production (prevents further sperm entry)

Question 22

In what phases are Oestrogen and Progesterone at their highest?

Answer 22

Oestrogen- Follicular Phase

Progesterone- Luteal Phase

Question 23

What do Granulosa cells release after ovulation

Answer 23

Progesterone