Folliculogenesis

Question 1

What has to be achieved to reproduce?

Answer 1

much more than just sexual intercourse

• Differentiation into male or female
• Sexual maturation
• Production, storage and release of sufficient supply of eggs and sperm
• correct number of chromosomes in eggs & sperm
• Eggs and sperm have to meet ie. gamete transport
• Creation of new individual with genes from both parents
• To nurture individual until capable of “independent life”

Question 2

cell that become eggs or sperm originate from where?

Answer 2

primordial germ cells

Question 3

primordial germ cells are first identifiable where?

Answer 3

in the yolk sac of the developing foetus at 3 weeks

Question 4

what happens to primordial germ cells

Answer 4

they undergo many rounds of mitosis, migrate to genital ridge which because the gonad
-PGC’s differentiate into male or female games depending on the gonadal development

Question 5

when germ cells are in the ovary what do they become?

Answer 5

oogonia

Question 6

what are oogonia?

Answer 6

egg-precursors

Question 7

summary of oogonia - primary oocytes - primordial follicles

Answer 7

• oogonia are diploid and multiply by mitosis
• once mitosis stops they enter into the first stage of meiosis
• no more division occurs and they are primary oocytes
• surrounded by layer of GC – now known as primordial follicle
• establishment of the true “ovarian reserve”

Question 8

before birth what happens?

Answer 8

massive loss of oocytes

-when you’re born you have your entire stock of primordial follicles

Question 9

how long do primary oocytes remain in the fist phase of meiosis?

Answer 9

until they are ovulated or die

Question 10

when do chromosomes replicate?

Answer 10

s phase of cell cycle

Question 11

what happens during chromosome replication?

Answer 11

• remain attached at the centromere
• each copy known as a chromatid
• 2 copies are identical to each other and are called “sister” chromatids
• exact copy of original chromosomes

Question 12

phases of mitosis?

Answer 12

prophase
metaphase
anaphase
telophase

Question 13

how does meiosis differ to mitosis?

Answer 13

• in meiosis the homologous chromosomes line up adjacent to 1 another
• allows recombination and variation to occur
• line up at the spindle and arrest at this stage for decades

Question 14

where are primary oocytes located?

Answer 14

they are packed into the outer layer of the ovary

-the cortex

Question 15

formation of primordial follicles

Answer 15

• primary oocytes will remain in this phase for many years. therefore, each one gets surrounded by many protective layers
• in the foetal ovary, surrounding cells condense around the oocyte and differentiate into granulosa cells
• GC’s secrete an acellular layer called the basal lamina
• whole structure is now a primordial follicle

Question 16

why do we have a massive loss of oocytes when we are born?

Answer 16

because those which haven’t formed a follicle properly will die off, those which haven’t undergone mitosis properly or the first stages of meiosis will die off.

Question 17

what is folliculogenesis?

Answer 17

the growth and development of follicles from the resting stages through to ovulation

Question 18

after puberty what happens?

Answer 18

a cohort of follicles grow every day

Question 19

primordial follicle growth

Answer 19

• granulosa cell multiplication
• secretion of another protective acellular layer, zona pellucida - stays attached after ovulation and protects the egg
• in the adolescent ovary, second layer of cells differentiates around the basal lamina - theca cells

Question 20

what are steroid producing?

Answer 20

the theca and granulosa cells

-sustain the follicle and feed into the menstrual cycle

Question 21

what does FSH drive?

Answer 21

most of folliculogenesis, but early growth is independent of FSH

Question 22

what happens in FSH deficient patients?

Answer 22

follicles will still continue early growth but then die

Question 23

formation of an antral/secondary follicle

Answer 23

• follicle grows and rapidly increases in diameter
• granulosa cells divisions increase, gaps form in granulosa cell layers
• gaps consist of follicular fluid-filled spaces which form an antrum
• as the antrum and follicular fluid volume expands, oocyte is displaced to one side

(follicles with an antrum are known as antral/secondary follicles)

Question 24

what is an antral follicle

Answer 24

-characterised by an “antrum” (cavity)
-contains fluid formed as exudate of plasma containing secretory products of oocyte & GC
Known as “follicular fluid”

Question 25

preovulatory or Graafian follicle

Answer 25

• as the fluid filled spaces expand, the granulosa cells are pushed towards the edge
• eventually the egg is sitting within the follicular fluid surrounded by granulosa cells, now known as cumula cells
• this is a cumulus oocyte complex, and it is then ovulated

Question 26

follicle initiation

Answer 26

cohort of early follicles leaving the resting pool and grow continuously

Question 27

follicle recruitment

Answer 27

cohort of early follicles recruited will NOT continue to grow unless they reach the correct size to respond to FSH changes in the menstrual cycle

(only one will be selected for ovulation)

Question 28

gonadotrophin independent growth?

Answer 28

primordial and preantral follicle

Question 29

gonadotrophin dependent growth?

Answer 29

antral and ovulatory - need FSH to grow

Question 30

role of the theca?

Answer 30

• very detailed blood supply

- bringing growth factors and hormones to sustain follicle growth

Question 31

two-cell–two-gonadotropin theory

Answer 31

• LH drives androgen production from cholesterol in theca cells
• androgens go into circulation and across into granulosa cells
• FSH binding to FSH receptors on granulosa cells drives oestrogen production in granulosa cells, formed from androgens (aromatase)

Question 32

what does aromatase catalyse?

Answer 32

the conversion of androgens to oestrogens

-only exists in granulosa cells

Question 33

what happens to the majority of primordial follicles?

Answer 33

die

Question 34

when do the follicles finish meiosis 1?

Answer 34

just before ovulation