Female Sex Hormone Physiology

Question 1

List the 3 phases of the ovarian cyle

Answer 1

i. Follicular
ii. Ovulation
iii. Luteal

Question 2

List the events occurring in stage I of follicular phase

Answer 2

1. Oogonium (diploid stem cell) develops into primordial follicle
2. Primordial follicle develops into primary follicle

Question 3

What changes occur in the transformation of an oogonium into a primordial follicle?

Answer 3

Arrested in prophase I

Surrounded by follicular cells

Question 4

Across what duration does the oogonium form a primordial follicle?

Answer 4

From birth till puberty

Question 5

What changes occur in the transformation of a primordial follicle to a primary one?

Answer 5

Squamous-like cells surrounding the primary oocyte become cuboidal cells

Oocyte enlarges

Question 6

List the events occurring in stage II of follicular phase

Answer 6

1. Primary follicle develops into secondary follicle

2. Secondary follicle becomes a Graafian follicle

Question 7

Describe the changes in a primary follicle to form a secondary follicle

Answer 7

• Follicular cells proliferate till they have more than one layer around the oocyte and become GRANULOSA CELLS
  
  • Secrete a glycoprotein rich substance that surrounds the oocyte – Zona Pellucida – separates the granulosa cells from the oocyte.
• A layer of connective tissues condenses around the follicle forming theca folliculi (theca externa & interna)
• Clear liquid accumulates between the granulosa cells and coalesces to form ANTRUM

Question 8

Describe the changes in a secondary follicle to form a Graafian follicle

Answer 8

• Antrum expands with fluid till it isolates the oocyte which is surrounded by cumulus oophorus
• Follicle attains full size (Graafian follicle)– 2.5cm in diameter

Question 9

List the events occurring in stage III of the follicular phase

Answer 9

Dominant follicle is formed/chosen

Oocyte completes meiosis I to form a secondary oocyte and a polar body

Question 10

Explain the role of hormones in follicular phase (stage III)

Answer 10

Pituitary FSH causes:

a) Follicles to grow
b) Granulosa cells to secrete more Activin and FSH
- Activin stimulates FSH production and binds to FSH receptors on granulosa cells
- Granulosa cells secrete aromatase, which increases the level of oestrogen

Increased oestrogen levels cause a -ve feedback effect on the pituitary - FSH and LH production falls.

Question 11

How is a dominant follicle chosen?

Answer 11

Fall in pituitary FSH and LH as a result of -ve feedback causes the levels of these hormones to be fairly low.

This level is only enough to stimulate the follicle with the highest number of FSH receptors which is the dominant follicle.

Rest of the follicles regress and die off.

Question 12

What is the role of the dominant follicle? What is the hormonal response as a result?

Answer 12

• Dominant follicle secretes oestrogen for the rest of the follicular phase.
   Rising levels of oestrogen makes pituitary more responsive to GnRH
   Once oestrogen reaches 200pc/mg = +ve feedback signal
   Pituitary releases large amounts of FSH and LH

Question 13

Describe the events of ovulation

Answer 13

• Occurs on the 14th day of a 28 day cycle
• Dominant follicle is at the peak of maturation when LH surges
• Graafian follicle will bulge from external surface of the ovary
• Ovary wall ruptures and secondary oocyte is released into the peritoneal cavity
• Oocyte is surrounded by corona radiata – outermost layer of cumulus oophorus

Question 14

Describe the events of the luteal phase

Answer 14

• Ruptured follicle collapses and the antrum filled with blood clot (corpus hemorrhagicum) is eventually absorbed
• Theca externa and interna, and granulosa cells form corpus luteum
• Under LH stimulation, corpus luteum produces progesterone, oestrogen and androgens
• On days 23-24 corpus luteum function declines spontaneously through luteolysis
• Corpus luteum remnant is replaced with dense connective tissue and forms corpus albicans