Ovarian function and control

Question 1

Oocytes recruit follicular cells to become primordial follicles and this …………………….

Answer 1

Is the reservoir we have at birth to ovulate from

Question 2

Early follicular growth is driven by …………….

Answer 2

growth factors not gonadotrophin (they don’t need LH or FSH at the start)

Question 3

How long does folliculogenesis take?

Answer 3

4-6 months

Question 4

Describe the process of folliculogenesis

Answer 4

The primordial follicles are sitting in the ovary and some signal tells them to start growing, they leave the resting pool (initial recruitment). The primordial follicle becomes a primary oocyte with one flattened layer of granulosa cells, it progresses to secondary follicle with further granulosa cell growth (which become more cuboidal) and a basement layer is formed as they develop. Stromal cells are formed and become known as theca cells.
The next stage is the antral follicle when the antrum is formed when spaces appear among the granulosum cells and this space grows and fills with fluid. The antral follicles also develop in waves.

Question 5

What are the three stages of antral follicle growth?

Answer 5

Recruitment, selection and dominance

Question 6

Describe recruitment of antral follicles

Answer 6

A cohort of follicles (10-20) are recruited
This is initiated by a wave of FSH
Some will undergo atresia which is follicular degeneration
The follicles secrete a small amount of oestradiol
Occurs even when in luteal phase as well as follicular phase

Question 7

Describe selection of antral follicles

Answer 7

The follicles have grown to 4-9mm
Dependant on FSH support
Produce oestradiol and inhibin which causes negative feedback on the pituitary gland and supresses FSH

Question 8

Describe the dominance stage of antral follicle growth

Answer 8

The selected follicle will grow into a large follicle >9mm and supress the smaller follicles growth.
Codominance of two large follicles is how two eggs are ovulated.
There is a Transition from FSH to LH dependence as LH receptor appear in granulosa cells
Increased oestradiol and inhibin production which is how it Inhibits growth of other follicles
Growth 1mm/day (cow); >3 mm/day (horse)

Remain for ~6 days and either Ovulate or undergo atresia
Depends on whether progesterone falls

Question 9

The dominant follicle will undergo atresia if which hormone is high?

Answer 9

progesterone (high in the luteal phase)

Question 10

How is oestradiol produced by the antral follicle?

Answer 10

Coordinated action of theca and granulosa layers
It is produced from cholesterol in a series of steps by the key enzyme: AROMATASE
Aromatase activity stimulated by FSH and LH

Question 11

Oocyte release from the ovary is stimulated by a surge in what hormone? what causes this surge?

Answer 11

LH surge stimulated by oestradiol

Question 12

When does the LH surge usually occur? Which animal is the exception?

Answer 12

The LH surge ususally occurs around the start of oestrus except in mares where there is a gradual increase in LH during oestrus.

Question 13

What does the pre-ovulatory LH surge cause?

Answer 13

fluid accumulates in maturing follicle & pressure increases
surface connective tissue of the ovary is weakened by increased synthesis of collagenase
ovarian smooth muscle cells contract
blood flow increases & local fluid accumulates
Causes completion of meiosis I but then meiosis II is arrested

Question 14

During lutenisation what do the granulosa and theca cells become?

Answer 14

Granulosa - Large luteal cell

Theca - Small luteal cell

Question 15

During lutenisation there is intense angiogenesis, why?

Answer 15

There is creation of new blood vessels because while the follicle was there the granular cells were avascular but as these turn into large luteal cells the blood vessels can breach the basement membrane

Question 16

During lutenisation the old follicle cells switch from producing oestradiol to producing which hormone?

Answer 16

Progesterone

Question 17

In a litter producing animal how many CL’s are there?

Answer 17

One per animal

Question 18

What is a luteotroph?

Answer 18

Hormone that supports the growth / function of corpus luteum eg LH or prolactin in rodents

Question 19

Which cells produce the most progesterone in the CL?

Answer 19

Large luteal cells

Question 20

What are the two regulatory steps in progesterone production?

Answer 20

The key regulatory step in progesterone production is the Transfer cholesterol to mitochondria and also Steroid acute regulatory factor (StAR)

Question 21

What does luteolysis allow in the non- pregnant female?

Answer 21

Pre-ovulatory follicular development and a return to oestrus

Question 22

What is the key luteolytic hormone?

Answer 22

Prostaglandin F2Alpha

Question 23

What normally initiates luteolysis

Answer 23

Initiation of luteolysis is caused by endometrial PGF2A in response to luteal oxytocin, this is a positive feedback loop.

Question 24

How does positive feedback cause luteolysis?

Answer 24

PGF2A gets to the ovary by the uterine vein which is closely associated with the artery coming back to ovary and diffuses counter currently. So just a small amount of PGF2A will cause a larger effect.

Question 25

What is the mechanism of luteolysis?

Answer 25

Reduced blood flow
Increase in macrophages & lymphocytes
Apoptosis and tissue resorption
Corpus albicans forms
Down regulation of steroidogenic enzymes
Rapid fall in progesterone

Question 26

Even though luteolysis is caused by a prostaglandins, the CL is only sensitive to them at certain times. In the Cow when is the CL unresponsive to PGF2A?

Answer 26

The first 6 days of the cycle, after then if injected it will bring the cow in to cycle again earlier