The Menstrual Cycle

Question 1

What are the five main hormones in the menstrual cycle?

Answer 1

1. Gonadotrophon releasing hormone
2. Lutenising hormone
3. Follicle stimulating hormone
4. Progesterone
5. Estradiol

Question 2

Describe the hormonal structure of the follicular/proliferative phase

Answer 2

GnRh stimulates FSH and LH –> FSH stimulates follicle growth and maturation –> follicle secrete estrogen –> estrogen exerts a negative feedback on FSH and positive feedback on GnRH –> LH levels increase

Question 3

Describe the hormonal elements of ovulation

Answer 3

Maturing follicle secretes a lot of estrogen –> GnRH stimulates a surge of LH –> LH surge allows for the oocyte to leave the follicle

Question 4

Describe the hormonal structure of the luteal/secretory phase

Answer 4

Estrogen levels drop –> corpus luteum secretes progesterone (and estrogen) –> negative feedback on the GnRH –> less LH and FSH –> progesterone levels drop as the corpus luteum degrades –> drop in progesterone and estrogen leads to endometrial bleeding –> GnRH levels increase due to lack of progesterone –> cycle begins again

Question 5

Describe the three core elements of the follicle

Answer 5

1. Primary oocyte
2. Theca cells
3. Granulosa cells

Question 6

Explain how estradiol is made

Answer 6

Theca cells bind to LH and create androstenedione and granulosa cells bind to FSH to create aromatase. Androstenedione + aromatase = 17B estradiol

Question 7

Explain how the corpus luteum makes progesterone

Answer 7

Lutenized granulosa cells react to the low levels of LH by increasing the activity of cholesterol side chain cleavage enzyme (P450scc). P450scc turns cholesterol to pregnenolone, which is a precursor to progesterone.

Question 8

Describe the endometrium during the proliferative phase under the influence of estrogen

Answer 8

• Estradiol induces growth and proliferation of the endometrium
• Spiral arteries grow
• Cervical mucus is hospitable to sperm

Question 9

Describe the endometrium during the secretory phase under the influence of progesterone

Answer 9

• Progesterone prepares the endometrium for conception
• Spiral arteries continue to grow and allow for more blood to form the uterine lining
• Cervical mucus becomes less hospitable to sperm

Question 10

What are the five cellular events of menstruation?

Answer 10

1. Loss of normal response to bleeding (haemostasis)
2. Loss of vascular integrity
3. Tissue breakdown
4. Endometrial re-epithelialisation
5. Vascular repair

Question 11

How does progesterone maintain normal response to bleeding?

Answer 11

Progesterone is crucial for normal clotting cascade as it enhances tissue factor expression

Question 12

Describe the loss of vascular integrity caused by progesterone withdrawal

Answer 12

There is severe vasoconstriction of endometrial spiral arteries which causes ischemic damage, leading to blood flowing out of the vessels and into the endometrium

Question 13

Explain endometrial re-epitheliazation

Answer 13

The epithelium spreads from the basal glands and the cells spread over the endometrium

Question 14

Describe the vascular regeneration process

Answer 14

Vascular endothelial growth factor (VEGF) and other angiogenic factors repair the open blood vessels

Question 15

Four categories of menstrual cycle disorders

Answer 15

1. Disorders of ovulation
2. Disorders of cycle length
3. Disorders of flow
4. Dysmenorrea

Question 16

What causes anovulatory bleeding?

Answer 16

1. Underlying polycystic ovary syndrome
2. Uncontrolled diabetes mellitius
3. Hypo or hyperthyroidism
4. Long term progestin-only contraceptives

Question 17

What are the five requirements for successful conception?

Answer 17

1. Normal ovulation (ovarian function)
2. Sperm maturation
3. Egg & sperm transport: healthy, mobile fallopian tubes
4. Successful fertilisation
5. Functioning endometrium