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Repro 313 > Follicular Development: Lecture 5 > Flashcards

Follicular Development: Lecture 5 Flashcards

1
Q

What is the order of follicular development?

A 
Primordial Follicle
Primary follicle
Secondary follicle
Mature (graafian or pre-ovulatory) follicle
(ovulation)
Corpus Luteum
Corpus Albans
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2
Q

Where is the primary oocyte located in the ovary?

A

The primary oocyte sit in the ovarian cortex near the tunica albuginea in clusters know as egg nests.

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3
Q

Describe the structure of the primordial follicle:

A

Primary oocyte is surrounded by a single layer of simple squamous (granulosa cells) cells.

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4
Q

What is the structure of a primary follicle?

A
  • Oocyte has secreted glycoproteins forming the ZONA PULLICIDA around the follicle
  • Condensation of ovarian stromal cells known as THECAL CELLS being to form around the follicle.
  • Still single(ish) layer of granulosa cells
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5
Q

What triggers the follicle to become larger?

A

FSH

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6
Q

When FSH stimulates the follicle to become larger, what happens exactly?

A

FSH stimulates the proliferation of granulosa cells surrounding the oocyte.

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7
Q

When does FSH take action?

A

Once the primary follicle has formed and it causes the formation of the secondary follicle.

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8
Q

What is the structure of the secondary follicle?

A
  • Large mass of proliferated granulosa cells.
  • These proliferating granulosa cells releases viscous follicular fluid that coalesces to form a single FOLLICULAR ANTRUM.
  • Innermost granulosa cells firmly attach to the zone pellucid and this is called the CORONA RADIATA.
  • Mass of loosely associated granulosa cells is known as the CUMULUS OOPHORUS.
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9
Q

What happens to the thecal cells during the development of the secondary oocyte?

A

The theca develops to become the inner glandular, highly vascular THECA INTERNA, and the surrounding fibrous capsule, the THECA EXTERNA.

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10
Q

What is defines a mature follicle?

A

As the follicular antrum grows, the oocyte becomes suspended in fluid, it is connected to the rim of peripheral granulosa cells by a thin stalk of cells.

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11
Q

What enables the follicle to be ovulated?

A

The rapid expansion of the follicular fluid results in a thing peripheral rim of granulosa cells, causing it to bulge out of the ovarian surface. This expansion and thinning continues until it ruptures and the follicle is ovulated.

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12
Q

What happens during ovulation?

A
  • Follicle ruptures at the stigma, carrying with it the follicle and a surrounding mass of cumulus cells.
  • Proteolytic enzymes are also involved.
  • The follicle is collected by the cilia of the fimbriae and swept into the oviduct along with the cumulus cells.
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13
Q

What happens to the ruptured follicle?

A

It becomes the corpus luteum.

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14
Q

What does the process of becoming the corpus luteum involve?

A
  • Antrum breaks down, as well as the basement membrane between the granulosa cells and the thecal layer.
  • Blood vessels invade.
  • Granulosa cells cease dividing and hypertrophy into lutein cells.
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15
Q

The transformation from granulosa cells to lutein cells is called? and is associated with?

A

Luteinisation and is associated with increasing secretions of progesterone.

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16
Q

What are the characteristics of lutein cells?

A
  • Rich in mitochondria
  • Smooth ER
  • Lipid droplets
  • lutein pigment - yellow.
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17
Q

How does the corpus lute transist into the corpus albicans?

A
  • There is luteal regression, involving ischemia, progressive cell death and failure of progesterone release.
  • Whitish scar tissue remain (corpus albicans) that is re-absorbed into the stroma)
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18
Q

Describe the process of fertilisation:

A

The sperm must penetrate the corona radiate and zone pellucida (acrosome reaction) to enter the follicular cytoplasm.
Once this is done, the secondary oocyte completes meiosis 2.
Cytoplasm is not divided equally leaving a second polar body to disintegrate.
Formation of a zygote.

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19
Q

If the secondary oocyte is fertilised what happens to the corpus luteum?

A

It persists past it two week life span. (continuous progesterone secretion)

20
Q

What prevents corpus luteum degeneration?

A

The secretion of hCG from the chorion of the embryo beginning 8 days post-fertilisation.

21
Q

How long is the average menstrual cycle?

A

28 days

22
Q

How is the menstrual cycle divided?

A 
Into two phases:
Follicular phase (1-ovulation)
Luteal Phase (ovulation-menstruation)
23
Q

What are the three phases of the endometrial cycle?

A

Menstruation
Proliferative
Secretory.

24
Q

Describe the menstrual flow;

A

50-150mL blood, tissue fluid, mucous, epithelial shedding from the endometrium.

25
Q

Learn the fluctuation of hormone levels in the course guide.

A

now, for the menstrual cycle

26
Q

In a brief overview, describe the hormonal fluctuation during menstruation:

A

Oestrogen dominance prior to ovulation.

Progesterone dominance post ovulation.

27
Q

What is the two cell gonadotrophin hypothesis?

A

IN early follicular phase their is elevated levels of FSH and LH.

FSH initiates the development of a number of primary follicles and increases the number of granulosa cells.

LH increases the number of thecal cells.

28
Q

What do thecal cells do with regards to steroidogenesis?

A

Thecal cells synthesise androgens. This is stimulated by LH which activates the rate limiting cholesterol desmolase via cAMP.

29
Q

What does FSH do with regards to ovarian steroidogenesis?

A

When FSH present, granulosa cells aromatise androgens to oestrogen’s.

30
Q

How many oocytes are present in gestation of a female foetus?

A

By 5 months around 7 million oogonia.

31
Q

A newborn girl has how many oocytes, and how many by the time she enters puberty?

A

Around 1-2million per ovary when born

Then around 3-400K by the time she enters puberty.

32
Q

What is the rate of follicle depletion?

A

1000/month either by atresia or entering the growth phase (dominant follicle selected)

33
Q

What is follicle depletion independent of?

A

Gonadotrophs.

34
Q

When does oogenesis cease?

A

Menopause

Does not cease on the pill.

35
Q

How many follicles being follicular recruitment

A

Every day ~20-30 follicles will begin growth and eventually die

36
Q

How is follicular maturation regulated?

A

Regulated by a balance between survival and atresia

37
Q

Describe the recruitment process.

A

Regular recruitment of primordial follicles into a pool of growing prenatal follicles beings at puberty.

Once a month 20-30 early astral follicles will be selected for further development. One of which will become the dominant follicle and will be ovulated.

38
Q

Initial growth of follicles in the recruitment process is due to?

A

BMP

39
Q

When does FSH come into play for follicular growth?

A

FSH binds to receptors the first appear on cells in the late pre-antral phase. Preventing follicular death due to atresia.

FSH receptors mainly found on granulosa cells.

40
Q

What is the FSH threshold?

A

The minimal FSH levels for follicular growth. This determines the number of follicles that grow and the duration of this level is known as the FSH window.

FSH must be 10-30% above threshold for follicular growth.

41
Q

What enables the dominant follicle to exist?

A

Better development potential such as:

  • FSH receptor numbers are higher
  • Better blood supply
  • Thus better response to FSH and better supply.
42
Q

What happens to the dominant follicle once it starts to grow?

A

It develops LH receptors in the granulosa cells and can be ovulated in response to LH surge.

43
Q

Fraternal twins are the result of?

A

Two follicles become co-dominated and are ovulated + fertilised at the same time.

44
Q

What assists dominant follicle selection?

A

Endocrine and intra-ovarian regulations re involved in the selection of the dominant follicle.

45
Q

Describe the hormone fluctuations of the dominant follicle:

A

Dominant follicle produces rising levels of Oestrodiol and inhibit (decreases FSH) but due to the increase of FSH receptors, cell proliferation continues.

Theca cells androgen is thought to assists in atresia of other follicles.

Repro 313 (20 decks)

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