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Repro > Folliculogenesis > Flashcards

Folliculogenesis Flashcards

1
Q

What has to be achieved to reproduce?

A
  • Differentiation into male or female
  • Sexual maturation
  • Production, storage and release of sufficient supply of eggs and sperm
  • Correct number of chromosomes in eggs and sperm
  • Eggs and sperm have to meet i.e. gamete transport
  • Creation of new individuals with genes from both parents
  • To nurture individual until capable of “independent life”
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2
Q

What cells do oocytes or sperm differentiate from?

A

Primordial germ cells (PGC)

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3
Q

When are PGCs identified?

A

In the yolk sac of the developing foetus at 3 weeks after conception

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4
Q

Describe the cycle of PGC

A
  • Undergo many cycles of mitosis
  • They migrate to the genital ridge in the foetus
  • The genital ridge becomes the gonad
  • Further differentiation of the PGC into male/female gametes depend on the sexual differentiation/development of the gonad i.e. into ovary or testis
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5
Q

What happens when PGCs enter the ovary?

A

Germ cells become oogonia when in the ovary.

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6
Q

What is oogonia?

A

Oogonia are egg-precursors

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7
Q

Describe the process of oogonia to primary oocytes

A

Oogonia diploid and multiply by mitosis. Once mitosis stops and they enter into meiosis, they are known as primary oocytes.

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8
Q

When are all the primary oocytes made?

A

They are made when the oogonia enters the 1st stage of meiosis. They remain in the first phase of meiosis until it is ovulated (or dies) - maybe up to 52 years.

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9
Q

Describe the duplication of chromosomes

A
  • Chromosomes replicate during S-phase
  • Remain attached at the centromere
  • Each copy is known as a chromatid, the 2 are identical, “sister” chromatids.
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10
Q

Overiew of Mitosis

A

Prophase, Metaphase, Anaphase, Telophase

  • DNA replication occurs during interphase and forms two sister chromatids that form a chromosome.
  • Sister chromatids separate and move to opposite ends of the cell.
  • During cytokinesis, the parent cell divides, forming two daughter cells. Each daughter cell has two copies of each chromosome.
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11
Q

Overview of Meiosis

A
  • Begins with the replication of chromosomes also.
  • Has two divisions; first division - the chromosome number is reduced, as the two homologous pairs are separated into two cells.
  • Second division, the replicated chromatids of each chromosome are separated. Meiosis begins with one diploid cells and produces four haploid cells.
    Both meiotic divisions has four stages similar to those in meiosis.
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12
Q

What is the difference between oogenesis and folliculogenesis?

A

The unequal division of cytoplasm during cytokinesis.

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13
Q

Describe the stages of oogenesis

A

Oogonium -> Primary oocyte -> Secondary oocyte + First polar body -> Mature ovum + polar bodies

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14
Q

Describe the stages of folliculogenesis

A

Primordial follicle forms around the primary oocyte making one of the first granulosa cell layers. Primary follicle then forms the zona pellucida.
Secondary follicle where the granulosa cells grow like layers of an onion.
Tertiary (Graafian) follicle where the theca cell layers, follicule fluid in antrum and granulosa cell layers.

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15
Q

What happens when there is a gonadotrophin surge at the middle of menstrual cycle?

A

It stimulates reentry of the oocyte into meiosis as far as metaphase II.

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16
Q

What surrounds oocytes and why?

A

They are surrounded by protective layers and cells as they are the most important cell in the body.

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17
Q

What happens to the cells around the oocyte in the foetal ovary?

A

The surrounding cells condense around the oocyte and differentiate into the granulosa cells.

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18
Q

What do the granulosa cells secrete?

A

An acellular layer called the basal lamina.

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19
Q

What is the structure of the primordial follicle?

A

Granulosa cells + basal lamina

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20
Q

What is the ovarian reserve?

A

The build up of primordial follicles at the beginning of birth.

21
Q

What is folliculogenesis?

A

The growth and development of follicles, from the earliest “resting” stages as laid down in the foetus, through to ovulation.

22
Q

What drives folliculogenesis?

A

FSH drives folliculogenesis but early growth is independent of FSH.

23
Q

What happens in FSH deficient people?

A

FSH-deficient patients or those with mutations of FSHr means that when FSH is suppressed, the follicles will still continue early growth but then die.

24
Q

When do gaps form in the granulosa cell layers?

A

As the follicle starts to grow, it increases rapidly in diameter and granulosa cell divisions increase.

25
Q

What is an antrum?

A

The gaps in the granulosa cell layers consist of fluid-filled spaces with follicular fluid.

26
Q

What divides the primary and secondary(antral) follicles?

A

Labelled by the presence or absence of antrum.

27
Q

What is an antral follicle?

A
  • Contains a cavity
  • Contains fluid formed as exudate of plasma containing secretory products of oocyte and granulosa cells.
  • Known as “follicular fluid”
  • As the follicular fluid volume and antrum expands, the oocyte is displaced to one side.
28
Q

Which follicles are not present on an ultrasound?

A

Pre-antral follicles but are present all the time until menopause

29
Q

What is follicle initiation?

A

A cohort of early follicles leaving the resting pool and growing continuously.

30
Q

What is follicle recruitment?

A

The continued growth of a follicle when it reaches the size where it will respond to changes in FSH that occur in the menstrual cycle.

31
Q

Why is only one follicle recruited?

A

The human pelvis is designed to carry a single fetus therefore, only one will be selected for ovulation.

32
Q

When does folliculogenesis start?

A

It starts from resting stage and NOT from antral stage in the MC.

33
Q

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

A

3 cycles

34
Q

Which parts of the cycle are gonadotrophin-independent?

A

Primordial and Pre-antral

35
Q

Which parts of the cycle are gonadotrophin-dependent?

A

Antral and Ovulatory

36
Q

Describe the structure of the antral ovarian follicle

A
  • Cumulus cells
  • Follicular fluid
  • Granulosa cell layer (60 million by ovulation)
  • Basement membrane
  • Theca layer
37
Q

What is the diameter of the dominant follicle?

A

Up to 20 mm

38
Q

Why is a theca vasculature important?

A

It is important as the follicle will now be open to circulatory influences.

39
Q

What does the ovarian follicle produce?

A

It produces steroids

40
Q

What is the 2-cell, 2-gonadotrophin theory?

A

Luteinizing hormone stimulates thecal cells to produce androgens.
Follicle-stimulating hormone stimulates granulosa cells to produce oestrogens from androgens.

41
Q

Describe how LH stimulates theca cells

A

It binds to the LH receptor which stimulates the theca cell to turn cholesterol to androstenedione which is then released into the circulation.

42
Q

Describe how FSH stimulates granulosa cells.

A

Androstenedione diffuse into the granulosa cell then, FSH binds to the FSH receptor. The aromatase enzyme converts androstenedione into estradiol that is then released into the follicle.

43
Q

Which receptors do Theca cells have?

A

Only have LH receptors not FSH receptors.

44
Q

Which receptors do Granulosa cells have?

A

Have FSH receptors and LH receptors.

45
Q

Why are LH receptors needed on granulosa cells?

A

They are acquired from mid-follicular phase on. The LH will then drive progesterone and oestrogen production as well.

46
Q

How is folliculogenesis controlled?

A

Hypothalamus releases GnRH to the anterior pituitary. This then produces FSH/LH which stimulates the production of oestrogen and progesterone. Then feedback influences the anterior pituitary and hypothalamus.

47
Q

What happens to follicles that don’t make it to the menstrual cycle?

A

Atresia

48
Q

Summarise follicle formation and growth

A

PGC differentiate into oogonia, proliferating by mitosis and enter into meiosis and meiotic arrest. These then form primordial follicles. There is basal growth of primordial follicles but they do not progress. Once puberty commences, PF initiate growth as a continuum, until all follicles depleted and woman enters into menopause. Eggs remain arrested in MI until ovulation, enter into MII and then arrest again.

Repro (11 decks)

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