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Reproduction (Physiology 2) > Folliculogenesis > Flashcards

Flashcards in Folliculogenesis Deck (43)
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1
Q

What has to be achieved in order for reproduction to occur?

A
  • Differentiation into male or female
  • Sexual maturation
  • Production, storage and release of sufficient supply of
    eggs and sperm
  • Correct no. 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”
2
Q

What are germ cells?

A

Cells that will become eggs or sperm are called primordial germ cells (PGC)

3
Q

When do PGCs first become identifiable?

A

PGCs first identifiable in the yolk sac of the developing foetus at 3 weeks after conception

4
Q

How do PGCs differentiate?

A
  • Undergo many cycles of mitosis
  • They migrate to the genital ridge in the foetus
  • The genital ridge becomes the gonad (testes/ovaries)
  • Further differentiation of the PGC depend on the
    development of the gonad i.e. ovary or testis
5
Q

How do PGCs differentiate into oocytes?

A

If PGCs enter the ovary they become oocytes

Germ cells become oogonia when in the ovary

Oogonia are egg-precursors, diploid and multiply by mitosis

Once mitosis stops and they enter into meiosis, known as primary oocytes

Surrounded by layer of GC – now known as primordial follicle

6
Q

Why are the mitotic divisions during PGC differentiation so significant?

A

All the eggs that a woman will ever have are made at this stage
The mitotic divisions are therefore critical

7
Q

What happens once to oogonia enters meiosis?

A

Once the oogonia enter the 1st stage of meiosis no more division occurs and they become primary oocytes

8
Q

How long do primary oocytes remain in meiosis?

A

The primary oocytes remains in the first phase of meiosis until it is ovulated (or dies) ~maybe for 52 years!

9
Q

During which phase of the cell cycle do chromosomes replicate?

A

Chromosomes replicate during S-phase of the cell cycle

Copies remain attached at the centromere

10
Q

What are chromatids?

A

As long as the replicate copies remain attached, each copy known as a chromatid → the 2 copies are identical to each other → “sister” chromatids

11
Q

What are the 4 stages of mitosis?

A

Prophase; Metaphase, Anaphase & Telophase

12
Q

In which ways are meiosis and mitosis similar?

A

Meiosis and mitosis begin the same way. Both are preceded by the replication of chromosomes.

13
Q

outline one way meiosis differs from mitosis

A

Meiosis has 2 divisions instead of one

14
Q

Describe what occurs during the first division in meiosis

A

Chromosome no. reduced, as 2 homologues of chromosome pair (each replicated into two chromatids attached by a centromere) are separated into 2 cells - each cell has one member of each homologous pair of chromosomes

15
Q

What happens during the second meiotic division?

A

Replicated chromatids of each chromosome are separated
Meiosis produces four haploid cells.

The orderly movements of chromosomes during meiosis ensure each haploid gamete produced contains one member of each homologous pair of chromosomes

16
Q

What are the stages of meiosis?

A

Each of the 2 meiotic divisions has four stages similar to those in mitosis: prophase, metaphase, anaphase, and telophase (I and II)

17
Q

How does oogenesis differ from regular meiosis

A

The difference in oogenesis is the unequal division of cytoplasm during cytokinesis.

18
Q

Where are primary oocytes located?

A

Primary oocytes are packed into the outer layer of the ovary: the cortex

19
Q

Why are the primary oocytes so heavily surrounded by cells?

A

Oocytes arguably the most important cell in the body and will be in the vulnerable 1st meiotic phase for many years
Therefore each one becomes surrounded by protective layers and protective cells

20
Q

What protects the oocyte when in the foetal ovary?

A

In the foetal ovary, the surrounding cells condense around the oocyte and differentiate into granulosa cells
The granulosa cells then secrete an acellular layer called the basal lamina

21
Q

What is the primordial follicle composed of?

A

consists of an oocyte surrounded by a single layer of flat, supporting granulosa cells

22
Q

What is the clinical definition of folliculogenesis?

A

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

23
Q

How many follicles are undergoing growth in the ovaries?

A

Most of the follicles in the ovary are not growing – after puberty a cohort grow each day

24
Q

What effect does follicle growth have on the granulosa cells?

A

As the follicles start to grow, the granulosa cells multiply and the oocyte secretes another protective acellular layer called the zona pellucida which stays attached after ovulation

25
Q

Where do theca cells originate?

A

Once growth of the follicles has started a second layer of cells then differentiate around the basal lamina: the theca

26
Q

What controls growth of follicles?

A

The factors controlling initiation of growth and the early stages are largely unknown

27
Q

What role does FSH have on folliculogenesis?

A

FSH drives most of folliculogenesis but early growth is independent of FSH i.e. driven by local factors
- Apparent in FSH-deficient patients or those with
mutations of FSHr
- Also means that even when FSH is suppressed eg. on
COCP, the follicles will still continue early growth but
then die

28
Q

What happens to the follicle size during growth?

A

As follicle starts to grow it increases rapidly in diameter and granulosa cells divisions increase, but gaps begin to form in the granulosa cell layers

29
Q

What are the gaps in the granulosa cells

A

These gaps consist of fluid-filled spaces which form an antrum & are filled with follicular fluid

30
Q

How are the 2 main phases of follicle growth identified?

A

2 main phases of follicle growth labelled by absence or presence of antrum

31
Q

What are the 2 main phases of follicle growth?

A

Follicles are preantral (primary follicles ) and when the follicle forms they are known as Antral (secondary folicle)

32
Q

What is the antrum?

A

The antrum is a fluid filled space and when it starts to fill up with fluid the granulosa cells are pushed to one side

33
Q

What is an antral follicle?

A

Characterised by a cavity (antrum)

Contains fluid formed as an exudate of plasma containing secretory products of oocyte and GC - follicular fluid

34
Q

How is the oocyte displaced in a follicle?

A

As follicular fluid volume and antrum expands, oocyte is displaced to one side

35
Q

Where are preantral follicles found?

A

Preantral follicles aren’t visible on u/s but are present all the time until menopause

36
Q

What is follicle initiation?

A

A cohort of early follicles leaving the resting pool and grow continuously

37
Q

When does follicle growth cease?

A

They will NOT continue to grow unless they reach the size at which they respond to changes in (2mm) FSH that occur in the menstrual cycle

38
Q

How does correct follicle recruitment occur?

A

Human pelvis designed to carry a single fetus therefore,

From the group that are recruited only one will subsequently be selected for ovulation

39
Q

What is the significance of follicle survival?

A

1000s of primordial follicles
most die through atresia, a few make it into the menstrual cycle
Only maintain one follicle which will eventually be ovulated

40
Q

Why is the theca vasculature so significant?

A

Significant to vasculature of follicle as it brings the circulatory signals particularly the gonadotrophins (FSH/LH)

41
Q

According to the 2-cell-2-gonadotrophin theory what is the effects of the hormone release?

A

Luteinizing hormone (LH) stimulates theca cells to produce androgens

Follicle-stimulating hormone (FSH) stimulates granulosa cells to produce oestrogens from androgens

42
Q

How is folliculogenesis regulated?

A

HPO axis (hypothalamic pituitary ovarian axis)

43
Q

Outline the HPO axis

A
  1. GnRH produced from hypothalamus acts on the anterior
    pituitary to produce the gonadotrophins (LH/FSH)
  2. These act on the ovary to drive antral follicle growth
    (pre antral follicle growth occurs independently of the
    HPO axis)
  3. The antral follicles produce oestrogen and progesterone
    which feedback on to the hypothalamus, regulating
    GnRH pathway