Menstrual cycle + hormones

Question 1

What are the 4 main purposes of the menstrual cycle?

Answer 1

1. Generate an oocyte
2. Facilitate fertilisation
3. Optimise endometrium for implantation
4. Protect developing embryo

Question 2

When does the follicular phase occur?

Answer 2

-Day 1-14 (if 28 day cycle)
-Aligns with menstrual phase + proliferative phase
-Oocyte released at day 14 (if 28 day cycle)

Question 3

What controls the menstrual cycle?

Answer 3

-Hypothalamo-pituitary ovarian axis
-Hypothalamus –> hourly pulsatile GnRH release
-GnRH –> anterior pituitary stimulation
-Anterior pituitary –> FSH and LH release from basophils
-FSH –> stimulates follicular activity, promoting estradiol production from granulosa cells
-LH –> triggers ovulation, promotes corpus luteum development and progesterone production

Question 4

Do oestrogens stimulate a positive or negative feedback loop on the hypothalamus?

Answer 4

-Rising oestrogen levels INHIBIT GnRH, LH and SH levels (ie NEGATIVE feedback loop)
EXCEPTION = near midcycle
-High oestrogen levels STIMULATE LH release, triggering ovulation (ie POSITIVE feedback loop)

Question 5

What is the role of GnRH and where is it secreted?

Answer 5

-A decapeptide
-Secreted by mid basal hypothalamic neurons in hourly pulses
-Stimulates release of LH and FSH from anterior pituitary
-Secretion affected by life stresses eg bereavement, anxiety, time zone, exercise, weight loss

Question 6

What is the role of FSH and where is it secreted?

Answer 6

-Stimulates follicular activity (generation of oocyte)
-Therefore promoting oestradiol production from granulose cells surrounding oocyte
-Secreted from basophils in anterior pituitary

Question 7

What is the role of LH and where is it secreted?

Answer 7

-Triggers release of oocyte from dominant follicle
-Promotes development of the corpus luteum and production of progesterone in the luteal phase
-Secreted from basophils in anterior pituitary

Question 8

What are the layers of the pre-antral follicle and what are its roles?

Answer 8

-Oocyte –> zona pellucida –> granulosa cells –> theca
-Granulosa cells forms corona radiata (protective layer) in later antral follicle
-Granulosa and theca cells produce progesterone and oestrogen

Question 9

How many primordial follicles are present at birth and how many develop to produce an egg?

Answer 9

-In foetus at 6 months = 2,000,000
-At birth = 750,000
-At puberty = 400,000
-450 develop to produce an egg, remainder degenerate

Question 10

What is the development of the follicles to ovulation?

Answer 10

1. Primordial follicle
2. Primary / pre-antral follicle
3. Secondary / antral follicle
4. Pre-ovulatory follicle
5. Ovulation
6. Corpus luteum left in ovary once egg is expelled

Question 11

What are the roles of the different follicular cell types?

Answer 11

-Theca interna cells = secrete androgens
-Granulose cells = convert androgens to estradiol 17-beta

Question 12

How is the corpus luteum formed?

Answer 12

-Once follicle is empty post-ovulation, granulosa cells undergo luteinisation by LH
-Forms the corpus luteum (lifespan = 14 days)
-If no fertilisation occurs, it degenerates to become the corpus albicans

Question 13

What changes happen to the endometrium during the proliferative phase?

Answer 13

-Estradiol the dominant hormone
-Promotes endometrium thickening
-Proliferation of stromal cells, glands and blood vessels
-By ovulation, the endometrium is 2-3mm thick

Question 14

What happens to the endometrium during the secretory phase?

Answer 14

-Progesterone the dominant hormone
-Promotion of secretion, increase in lipid and glycogen production, increased blood supply
-Endometrium becomes 4-6mm thick
-Optimal conditions for implantation of fertilised egg
–Stable, vascular, nutrient-rich

Question 15

What occurs to the endometrium during the menstrual phase?

Answer 15

1. Failed implantation
2. Progesterone levels fall –> destabilisation
3. Vasodilation - necrotic outer layers of endometrium separate from the uterus
4. Separated tissue and blood initiate uterine contractions –> expel contents

Question 16

Where is mucus produced and how does it change throughout the cycle?

Answer 16

-From the columnar glands in the cervix
-Mid-cycle = stringy and runny to facilitate sperm access at ovulation
-Luteal phase = tenacious and inelastic to prevents embryo from microbial infection / maintains integrity of the cervix during pregnancy

Question 17

What is mittelschmerz?

Answer 17

-Lower abdo pain associated with ovulation

Question 18

Where and when does implantation occur?

Answer 18

-Day 23
-Blastocyst implants into decide of uterus
-hCG produced instantly, detectable from day 9-10, falls off around 20 weeks
-Progesterone received from corpus luteum, until 10-12 weeks from which placenta takes over

Question 19

What is the main hormone in pregnancy?

Answer 19

-Progesterone

Question 20

How is the cardiovascular system affected by pregnancy?

Answer 20

-Increased circulating volume (5-7L)
-Increased HR
-Increased SVR
-Increased CO
-BP decreases unless there is pathology
–Drops to allow more blood to reach peripheral organs ie placenta

Question 21

How is the respiratory system affected by pregnancy?

Answer 21

-Increased RR
-Increased respiratory effort due to lung compression from uterus
-NB difficult to investigate for PEs

Question 22

How is the GI system affected by pregnancy?

Answer 22

-Gastric / intestinal motility reduced
–More likely to get heartburn and constipation

Question 23

How is the immune system affected by pregnancy?

Answer 23

-Down-regulation to prevent rejection of foetus
-Neutropenia
–Increased risk of infection eg UTIs v common

Question 24

How is the renal system affected by pregnancy?

Answer 24

-Poor ureteric drainage