Folliculogenesis

Question 1

What are the 4 things required for reproduction?

Answer 1

→ Differentiation into male or female
→ Sexual maturation

→ Production, storage and release sufficient supply of eggs and sperm
→ correct number of chromosomes in eggs and sperm
→ egg and sperm have to meet

Question 2

What are cells that will become egg or sperm called?

Answer 2

→ Primordial germ cells

Question 3

When are PGCs first identifiable?

Answer 3

→ in the yolk sac 3 weeks after conception

Question 4

What happens to the PGCs?

Answer 4

→ the cells undergo many cycles of mitosis

→ They migrate to the genital ridge

Question 5

What does the genital ridge become?

Answer 5

→ The gonad

Question 6

What does further differentiation of the PGCs depend on?

Answer 6

→ The development of the gonad

Question 7

What do germ cells become when in the ovary?

Answer 7

→ oogonia

Question 8

What are oogonia?

Answer 8

→ Egg precursors

Question 9

When oogonia enter meiosis what are they known as?

Answer 9

→ Primary oocyte

Question 10

What phase do primary oocytes remain in and until when?

Answer 10

→ They remain in the first phase of meiosis until it ovulates or dies

Question 11

Describe mitosis briefly

Answer 11

→ Spindle is formed
→ The chromatids are lined up one behind the other

→ They then separate to opposite poles of the cell
→ The cytoplasm divides and there are two identical cells

Question 12

Describe meiosis

Answer 12

→ Duplication of the chromatids
→ They line up adjacent to each other

→ Chromosome 1 lines up with chromosome 1 from the other parent
→ allows crossing over and biological variation
→ homologous chromosomes separate into two haploid cells
→ separate again to form gametes
→oocytes are arrested in meiosis 1 until LH surge

Question 13

where are primary oocytes packed?

Answer 13

→ Outer layer of the ovary : cortex

Question 14

What do the cells around the oocyte become in the fetal ovary?

Answer 14

→ Condense around the oocyte and differentiate into granulosa cells

Question 15

What do granulosa cells secrete?

Answer 15

→ Acellullar layer called the basal lamina

Question 16

What does a primordial follicle consist of?

Answer 16

→ Oocyte with granulosa cells and a basal lamina

Question 17

What do germ cells become in the ovary?

Answer 17

→ oogonia

Question 18

What type of cell are oogonia and how do they multiply?

Answer 18

→ Diploid

→ Multiply by mitosis

Question 19

What happens to the follicles at puberty and at menopause?

Answer 19

→ Follicles start growing at puberty

→ arrests at menopause

Question 20

What is folliculogenesis defined as?

Answer 20

→ Growth and development of follicles from the earliest resting stages as laid down in the fetus through to ovulation

Question 21

What happens as the follicles start to grow?

Answer 21

→ Granulosa cells multiply
→ Granulosa cells secrete basal lamina around it

→ oocyte secretes another protective acellular layer called the zona pellucida
→ Theca cells differentiate around the basal lamina

Question 22

What are theca cells and what is their purpose?

Answer 22

→ Steroid producing
→ they sustain the growth of the follicle and the oocyte
→condenses from interstitial cells in ovary

Question 23

What drives most of folliculogenesis?

Answer 23

→ FSH
→but early growth is independent of FSH i.e. driven by local factors
→Apparent in FSH-deficient patients or those with mutations of FSHr- we still see follicles in early stages

Question 24

What happens to follicles when FSH is suppressed eg on COCP?

Answer 24

→ The follicles will continue early growth but they die

Question 25

What happens in the second stage of follicle growth?

Answer 25

→ Increases rapidly in diameter → Granulosa cell divisions increase but gaps form in the cell layers → gaps form an antrum filled with follicular fluid- an exudate of plasma

Question 26

What are the two main phases of follicular growth?

Answer 26

→ Absence or presence of the antrum

Question 27

What are follicles with an antrum known as?

Answer 27

→ antral or secondary follicles

Question 28

What kind of cells do primordial follicles have and how do they look and grow?

Answer 28

→ flattened granulosa cells → grow in a slow and controlled manner → become cuboidal in shape

Question 29

Describe how primordial follicles physically change to become Graffian follicles

Answer 29

→ Granulosa cells → FSH causes granulosa cells to proliferate and the zona pellucida forms around the oocyte → theca cells are produced around the granulosa cells →Theca cells condenses around and bring blood vessels with it exudate →granulosa cell divisions increase and gaps form which are filled with follicular fluid →these join and form the antrum → the egg is then within follicular fluid

Question 30

What are the cells directly surrounding the oocyte called?

Answer 30

→ Corona radiata

Question 31

Where are primordial cells arrested in?

Answer 31

→ Meiosis I

Question 32

What is follicle initiation?

Answer 32

→ When a cohort of follicles leave the resting pool and grow continuously →starts from resting stage and NOT from antral stage

Question 33

What is follicle recruitment?

Answer 33

→ When the follicles are big enough to respond to changes FSH they start growing

Question 34

What do follicles need to continue growing?

Answer 34

→ FSH

Question 35

How long does the follicular phase last?

Answer 35

→ 14-15 days

Question 36

What is atresia?

Answer 36

→ When follicles die

Question 37

What steroids do the granulosa and theca cells produce?

Answer 37

→ Theca produces androgens which is stimulated by LH | → androgens go to granulosa and get converted to estrogen which is stimulated by FSH

Question 38

What is the zona pellucida made of?

Answer 38

→composed of three glycoproteins: ZP1, ZP2, and ZP3. | →Receptors on the sperm plasma membrane attach to ZP3.

Question 39

What happens to granulosa cells fluid builds up?

Answer 39

→push granulosa cells outward and they are known as mural granulosa cells →Cells around the egg become the cumulus complex

Question 40

Are pre-antral follicles visible on ultrasound?

Answer 40

Pre-antral follicles are NOT visible on u/s but are present all the time until menopause

Question 41

How many cycles does it take for a follicle to go from resting stage to ovulation?

Answer 41

3 cycles

Question 42

Why are theca cells vascularised?

Answer 42

→so follicle is open to influences of surrounding circulation and anything produced by follicle can enter circulation

Question 43

What is the two-cell-two-gonadotropin theory?

Answer 43

→luteinizing hormone stimulates thecal cells to produce androgens →follicle-stimulating hormone stimulates granulosa cells to produce oestrogens from androgens.

Question 44

What is needed for the conversion of cholesterol to androstenedione?

Answer 44

LH and LHr found only on theca cells

Question 45

What is needed for the conversion of androstenedione to oestradiol?

Answer 45

→aromatase | →FSH found only on granulosa cells

Question 46

When are LHr found on granulosa cells?

Answer 46

→when there's selection of dominant follicle which acquires LHr allowing it to make progesterone and oestrogen via delta4 pathway