The Menstrual Cycle

Question 1

What kind of secretion of GnRH does there have to be?

Answer 1

→ pulsatile

Question 2

What does the antral follicle produce and what does this do?

Answer 2

→ Estrogen
→ Progesterone
→ feedsback to hypothalamus and pituitary

Question 3

What is the first day of the menstrual cycle?

Answer 3

→ The first day that bleeding occurs

Question 4

What is the length of an ideal menstrual cycle?

Answer 4

→ 28 days

Question 5

What is the follicular phase?

Answer 5

→ Growth of follicles until ovulation

Question 6

What is the main hormone in the follicular phase?

Answer 6

→ Estrogen

Question 7

What happens to the follicle after ovulation?

Answer 7

→ It becomes the corpus luteum

Question 8

What does the corpus luteum produce?

Answer 8

→ Progesterone

Question 9

What kind of feedback does progesterone have?

Answer 9

→ negative

Question 10

Describe the hypothalamic/ovarian axis

Answer 10

1) Progesterone produced from the corpus luteum exerts negative feedback on the hypothalamus
2) If there is no pregnancy the CL dies and progesterone levels drop - no negative feedback
3) FSH levels rise again - intercycle rise in FSH
4) the early antral follicles respond to FSH and grow again
5) the follicles are producing estrogen
6) This exerts a negative feedback and FSH drops
7) the antral follicles start to die except the dominant one
8) the dominant follicle grows exponentially and produces a lot of estrogen
9) Estrogen levels are sustained for 48 hours over 300pmol
10) there is positive feedback which results in a big increase in LH but not FSH because the dominant follicle produces inhibin which inhibits FSH
11) complettion of Meiosis I and entry into meiosis II
12) LH produces proteases which ‘cut’ the oocyte out and cause it to be ovulated
13) It also triggers luteinization
14) CL produces progesterone

Question 11

Why is the intercycle rise and fall in FSH important?

Answer 11

→ It allows the selection of a single follicle

Question 12

What is the rise in FSH for?

Answer 12

→ Selection of antral follicles

Question 13

What is the drop in FSH for?

Answer 13

→ The dominant follicle survives and the others die off

Question 14

What type of growth occurs consistently?

Answer 14

→ Pre antral growth

Question 15

What kind of follicles need FSH to grow?

Answer 15

→ follicles that have an antrum

Question 16

What is the FSH threshold hypothesis?

Answer 16

→ One follicle from the group of antral follicles is at the right stage at the right time
→ It has the most number of FSH receptors
→ It becomes the dominant follicle which goes on to ovulate

Question 17

Describe how the dominant follicle survives the fall in FSH?

Answer 17

→ The gene which produces the LH receptor is switched on
→ Follicle responds to LH
→ increases FSH receptors so it is responsive to falling levels of FSH
→ increases the number of granulosa cells

Question 18

What receptors do theca cells have?

Answer 18

→ LH receptors

Question 19

What do theca cells produce?

Answer 19

→ androgen

→ progesterons

Question 20

What is the pathway to make estrogen?

Answer 20

Acetate
    ↓
Cholesterol
     ↓
Pregneneolone
      ↓
progesterone
       ↓
testosterone/androstenedione
       ↓
Estrogens

Question 21

What are the three things that can affect the hypothalamic axis?

Answer 21

→ Stress
→ hyperinsulinemia
→ Adipocytes

Question 22

Why are estrogen levels raised at the end of the follicular phase?

Answer 22

→ The dominant follicle produces a lot of estrogen

Question 23

What does the raised estrogen level (produced by the dominant follicle) cause?

Answer 23

→ Estrogen feedback switches from - to +
→ Massive release of LH from the pituitary
→ triggers ovulation

Question 24

Describe ovulation

Answer 24

→ Blood flow to the follicle increases
→ Increase in vascular permeability which increases intra-follicular pressure
→ stigma on the ovary wall
→ local release of proteases
→ A hole appears in the ovary wall and ovulation occurs

Question 25

What happens to the egg after ovulation?

Answer 25

→ Collected by the fimbria

→ progresses down the tube by peristalsis and action of cilia

Question 26

What is the advantage of remaining in meiosis I ?

Answer 26

→ Permits the oocyte to retain all of the DNA and remain as large as possible

Question 27

What happens to the chromosomes when the egg becomes a secondary oocyte?

Answer 27

→ 1/2 the chromosomes are put in a small package in the egg called the 1st polar body

Question 28

If pregnancy occurs what is the CL supported by?

Answer 28

→ LH

→ HcG

Question 29

What are the functions of progesterone?

Answer 29

→ Alters secretions in cervix

→ Prepares endometrium

Question 30

What is the lifespan of the CL?

Answer 30

→ 14 days