Menstrual Cycle

Question 1

What are the 2 phases of the menstrual cycle?

Answer 1

• follicular phase
• luteal phase

Question 2

When does the follicular phase occur?

Answer 2

• occurs from the start of menstruation to the moment of ovulation
• the length is variable, but it is 14 days in a 28 day cycle

the ovum is inside a follicle that is developing during this phase

Question 3

When does the luteal phase occurs?

Answer 3

• this occurs from the moment of ovulation to the start of menstruation
• this is the final 14 days of the cycle
• the luteal phase is ALWAYS 14 days in length

the ovum has exited the ovary during ovulation and the remnants are the corpus luteum

Question 4

When does ovulation always occur?

Answer 4

14 days before the end of the menstrual cycle

e.g. day 14 of a 28 day cycle
or day 16 of a 30 day cycle

Question 5

What are follicles?

Answer 5

• from puberty, the ovaries contain a finite number of cells that have the potential to develop into eggs
• these cells are oocytes
• granulosa cells surround the oocytes to form follicles

Question 6

What are the 4 stages of follicle development in the ovaries?

Answer 6

• primordial follicles
• primary follicles
• secondary follicles
• antral follicles / Graafian follicles

Question 7

How do follicles initially mature within the ovary?

Answer 7

• the process of primordial follicles maturing into primary + secondary follicles is occurring ALL THE TIME
• this is independent of the menstrual cycle
• secondary follicles develop the receptors for FSH
• further development after the secondary follicle stage requires FSH

Question 8

How do the secondary follicles develop further?

Answer 8

• at the start of the menstrual cycle, FSH stimulates further development of the secondary follicles
• the granulosa cells surrounding them secrete increasing amounts of oestradiol (oestrogen)

Question 9

What is the effect of oestradiol secretion by the granulosa cells?

Answer 9

• it has a negative feedback effect on the pituitary gland
• this reduces the levels of FSH + LH
• rising oestrogen thins the cervical mucus, allowing sperm to penetrate the cervix around the time of ovulation

Question 10

What happens to only one of the developing follicles during the menstrual cycle?

Answer 10

• one follicle develops further than the others and becomes the dominant follicle
• an LH surge prior to ovulation causes the dominant follicle to release an ovum from the ovary
• this is ovulation

Question 11

What is meant by the LH surge?

Answer 11

• just before ovulation, there is a dip in oestrogen levels
• this causes a spike in LH
• this causes the dominant follicle to reach the surface of the ovary and release the ovum

Question 12

What happens to the follicle that released the ovum after ovulation?

Answer 12

• it collapses + becomes the corpus luteum
• this secretes high levels of progesterone
• it also secretes a small amount of oestrogen

this is the start of the luteal phase

Question 13

What are the roles of progesterone secreted by the corpus luteum?

Answer 13

• it maintains the endometrial lining
• it causes the cervical mucus to become thick and no longer penetratable

Question 14

What is the fate of the corpus luteum if fertilisation occurs?

Answer 14

• the syncitiotrophoblast of the embryo secretes human chorionic gonadotrophin (hCG)
• hCG maintains the corpus luteum
• without hCG, the corpus luteum degenerates

Question 15

What is the fate of the corpus luteum if fertilisation does NOT occur?

Answer 15

• in the absence of hCG, the corpus luteum degenerates
• the production of oestrogen + progesterone ceases
• this causes the endometrium to break down and menstruation to occur

Question 16

In addition to degeneration of the CL, what else facilitates menstruation?

Answer 16

• release of prostaglandins by the stromal cells of the endometrium
• prostaglandins encourage the endometrium to break down + uterus to contract

Question 17

On what day of the menstrual cycle does menstruation start?

Answer 17

• menstruation starts on day 1 of the cycle
• the negative feedback from oestrogen / progesterone on the pituitary gland ceases
• this allows the levels of FSH + LH to begin to rise and the cycle to restart

Question 18

What is involved in menstruation?

Answer 18

• the superficial + middle layers of the endometrium separate from the basal layer
• tissue is broken down inside the uterus and released via the cervix / vagina
• the release of this substance lasts between 1-8 days

Question 19

What is involved in the hypothalmo-pituitary-ovarian axis?

Answer 19

• the hypothalamus releases gonadotrophin-releasing-hormone
• this stimulates the release of FSH + LH by the anterior pituitary gland
• oestrogen released by the granulosa cells suppresses their release

Question 20

What factors can affect the secretion of GnRH?

Answer 20

• bereavement
• anxiety
• time zone
• working day / night shifts
• exercise
• weight loss / gain

Question 21

What is the overall function of FSH?

Answer 21

• stimulates follicular development
• this promotes the production of estradiol from granulosa cells

Question 22

What is the overall function of LH?

Answer 22

• triggers the release of an egg from the dominant follicle
• promotes development of the corpus luteum + production of progesterone

Question 23

What is the effect of the COCP on this cycle?

Answer 23

• it contains both estradiol + progestogen
• this inhibits GnRH and LH / FSH
• this prevents ovulation
• the endometrium remains thin and the cervical mucus remains thick

progestagen = synthetic progesterone