Lecture 7 - Menstrual Cycle

Question 1

Ovarian cycle

Answer 1

Provide an environment for fertilisation

Question 2

Uterine cycle

Answer 2

Receives fertilised oocyte and allows implantation

Question 3

Female HPG axis

Answer 3

1. Pulsatile GnRH released from the hypothalamus
2. Stimulates the anterior pituitary to release FSH and LH
3. FSH stimulates granulocytes and theca interna and externa cells to proliferate
4. FSH causes granulosa cells of the follicles to release oestrogen and inhubin and causes follicles to mature.

LH causes theca interna cells to release androgens which are aromatised to oestrogen under the influence of FSH.

5. Oestrogen at low concentrations has a negative feedback on the hypothalamus. As follicles develop, oestrogen concentration increases and exerts a positive feedback
6. Once the dominant follicle has been selected, inhibin causes negative feedback on the anterior pituitary so follicles stop maturing
7. Oestrogen exerts a positive feedback on the hypothalamus, anterior pituitary and granulosa cells so oestrogen and inhibin are still produced.
8. Once, LH conc is more than FSH, ovulation occurs

Question 4

Male HPG axis

Answer 4

1. Hypothalamus releases GnRH in pulsating manner as there is no ovarian hormone production and no negative feedback
2. Stimulates the anterior pituitary to release FSH and LH
3. FSH stimulates the sertolli cells to produce sperm and LH stimulates the Leydig cells to produce testosterone

Question 5

Pulsatile release of GnRH

Answer 5

Prevents receptors becoming desensitised to hormone

Question 6

Phases of the ovarian cycle

Answer 6

Follicular phase

Luteal phase

Question 7

Role of inhubin

Answer 7

Prevent FSH stimulating more than 1 dominant follicle

Question 8

Dominant follicle

Answer 8

Graafian follicle
Large antrum
Ready to be released at ovulation

Question 9

Which phase of the ovarian cycle can be varied?

Answer 9

Follicular phase

Question 10

Ovulation

Answer 10

Mature oocyte is extruded through the ovarian capsule into the peritoneal cavity where it is picked up by fimbrae and transported to the fallopian tube

Meiosis I is completed and Meiosis II starts

Question 11

Follicle after ovulation

Answer 11

The follicle now without the oocyte is leuitenised (yellow)

Secretes oestrogen and progesterone in large quantities

Question 12

Progesterone

Answer 12

Progesterone with oestrogen causes negative feedback on the hypothalamus and anterior pituitary so LH concentration decreases

Question 13

Luteal phase

Answer 13

Corpus luteum lasts for 14 days and waits for fertilisation and implantation.

Without fertilisation, the corpus luteum degenerates and oestrogen, progesterone and inhubin concentrations decrease.

No negative feedback so cycle starts again

Question 14

Uterine cycle phases

Answer 14

Proliferation phase - prior to ovulation

Secretory phase - after ovulation

Question 15

Endometrium

Answer 15

Stratum functionalis layer: Sheds during menstruation

Stratum basalis: contains stem cells and allows regrow the at the start of the cycle

Proliferates in response to oestrogen - thick and fat

Becomes more glandular and secretory in response to oestrogen and progesterone

Prevents blastocyst from implanting too far via the decidual reaction

Question 16

Layers of uterus

Answer 16

Endometrium - functional and basal layer

Myometrium - muscular layer

Question 17

Proliferation phase

Answer 17

Create a good environment for fertilisation

The functional layer proliferates and thickens
Simple straight glands coil

Question 18

Secretory phase

Answer 18

Progesterone causes coiled glands to become secretory

Blood supply is established - spiral arteries

Question 19

Fertilised oocyte

Answer 19

Syncytiotrophoblast releases beta - HCG which maintains the corpus luteum, maintaining oestrogen and progesterone

Question 20

Beta HCG

Answer 20

Beta human chorionic gonadotropin

Analogous to LH
Maintains the corpus luteum so oestrogen and progesterone is continually produced until the placenta takes over

Pregnancy test

Question 21

Oestrogen in the proliferative phase

Answer 21

Proliferation of the myometrium and endometrium
Increases fallopian tube motility
Thin, alkaline cervical mucous is produced

Question 22

Progesterone in the secretory phase

Answer 22

Create environment viable for pregnancy

Decreases myometrium motility
Further thickening of the endometrium
Thick, acid cervical mucus
Increased body temperature

Question 23

Normal menstrual cycle

Answer 23

21 - 35 days

Variation due to variation in follicular phase

Question 24

Longer follicular phase

Answer 24

Longer follicular phase cause longer proliferative phase so endometrium is thicker.

Therefore more bleeding during menses

Question 25

Suppression of menstrual cycle

Answer 25

Physiological:
Pregnancy
Lactation (early)

Emotional stress
Low body weight - 47kg

Question 26

Immediate nutrition

Answer 26

Histiotrophic nutrition - glycogen

Endometrial glands deposit lipids and glycogen into the endometrium before the placenta is developed

Question 27

Why give continuous GnRH to someone with endometriosis?

Answer 27

Desensitises the receptors therefore decreasing menstruation