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Reproductive Anatomy > Folliculogenesis, Oogenesis and Ovulation > Flashcards

Folliculogenesis, Oogenesis and Ovulation Flashcards

1
Q

Define folliculogenesis

A

development of follicles to produce mature ova

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2
Q

Define oogenesis

A

development of primary egg cells into mature ovum competent for fertilisation

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3
Q

Define ovulation

A

release of the ova from the ovary

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4
Q

What tissues are present in the ovary cortex?

A

endocrine
gametogenic

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5
Q

What tissue does the ovary medulla consist of?

A

supportive tissue - blood and nerves

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6
Q

What are the differences between species in the ovary cortex and medulla?

A
  • cow/sow/sheep - medulla inner surface and cortex outer surface
  • mare - inversed
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7
Q

Where does ovulation occur in different species?

A
  • cow/sow/sheep - over surface of ovary
  • mare - ovulation fossa
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8
Q

What are the 2 stages of oogenesis?

A

prenatal
after puberty during oestrus cycle

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9
Q

Describe prenatal oogenesis

A
  • occurs during foetal development on outer surface of ovary where cortex will form
  • primordial germ cells diploid
  • 2N oogonia formed via mitosis - become diploid again
  • primary oocyte division via meiosis with aim of forming haploid cell
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10
Q

What does the process of prenatal oogenesis maximise?

A

no. gametes in order to be as prolific as possible

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11
Q

Describe primary mieosis oocyte division in prenatal oogenesis

A
  • interphase and prophase I of meiosis I
  • mieotic inhibitors halt at prophase I and cause nuclear arrest
  • female born with no. gametes for lifetime
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12
Q

Describe post puberty oogenesis

A
  • Not all primary oocytes come out of nuclear arrest all at once
    ○ Recruitment and selection phase - protects primary oocyte as nucleus remains dormant
    ○ Still see activity - oocytes have cytoplasmic and formation of Zona Pelucida
    § Translucent ring around cytoplasm of the oocyte
    • Of primary oocytes selected:
      ○ During oestrus cycle a no. follicles containing primary oocytes start to develop
      § Some become atretic and die
      ○ Meiosis I has potential to resume in a primary oocyte that has the potential to ovulate and has a mature cytoplasm
      ○ Meiotic inhibitors removed by LH following surge of LH close to ovulation
      ○ Meiosis I resumes and completes
      § Secondary oocyte (1N) will ovulate
      § Most oocytes won’t get to this stage
      ○ In bitch - meiosis I won’t resume until after ovulation
      Meiosis II can only occur after fertilisation - produces mature ovum
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13
Q

What are the 4 stages of oocyte maturation and what is essential to support these?

A
  • prenatal mitotic division
  • nuclear arrest
  • cytoplasmic growth
  • resumption of meiosis

folliculogenesis essential

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14
Q

Describe the overall process of Folliculogenesis

A
  • oogonia - no follicle
  • meiotic division of oogonia to form primary oocyte
  • primordial follicle develops into primary follicle
  • develops to secondary then tertiary follicle
  • preovulatory follicle developed
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15
Q

Describe the meiotic division of oogonia in folliculogenesis

A
  • primary oocyte held in nuclear arrest until post-pubtery & oestrus
  • primodrial (first) follicle appears - very immature, flattened granulosa cells in close proximity to primary oocyte and outer basement membrane
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16
Q

Describe how primordial follicle develops into primary follicle in folliculogenesis

A
  • primary oocyte still present
  • granulosa cells more cuboidal
  • females born with lifetime supply of primordial and primary follicles but not all will be ovulated
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17
Q

Describe how the secondary follicle is developed in folliculogenesis

A
  • 2 or more layers of granulosa cells
  • small number of theca cells that surround granulosa cells - have receptors for hormones
  • zona pelucida starts to form around primary oocyte
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18
Q

Describe how the tertiary follicle is developed

A
  • primary oocute surrounded by granulosa cells
  • basement membrane and then 2 extra layers of theca cells
  • as follicle develops - antrum (cavity) forms
19
Q

Describe the 2 layers of theca cells in the tertiary follicle

A
  • theca externa: connective tissue, fairly loose structure that supports developing follicle
  • theca interna: role in hormone production and sensitivity
20
Q

Describe the antrum in the tertiary follicle

A
  • filled with follicular fluid from oocyte and granulosa cells
  • fluid contains hormones and proteins to support developing oocyte
21
Q

Describe the preovulatory follicle and how it is formed

A
  • follicle that ovulates
  • called graafian follicle or mature follicle
  • FORMED:
  • antrum increases in size due to fluid
  • granulosa cells group together to form cumulus oophorus in which secondary oocyte sits on
  • theca interna and externa still present
22
Q

When manipulating the cycle, which phase is targeted and why?

A

antral phase because it is dependent on gonadotropin hormones therefore occurs within oestrus cycle

23
Q

Describe the preantral phase

A

oogonia
primordial follicle
primary follicle
secondary follicle

24
Q

Describe the antral phase

A

tertiary hormone and preovulatory hormone
gonadotropic hormone dependent

25
Q

Describe antral follicle dynamics

A
  • recruitment from ovarian follicular pool
  • selection
  • dominance
  • antresia
26
Q

Describe selection in antral follicle dynamics

A
  • small follicles recruited and start to grow & secrete oestradiol in small quantities
  • some selected to become medium follicles: grow and secrete more
  • some selected again to become dominant follicles
27
Q

Describe dominance in antral follicle dynamics

A

dominant follicles will go onto produce more oestradiol and become the pre-ovulatory follicles

28
Q

Describe atresia in antral follicle dynamics

A

over 90% of follicles die due to insufficient blood supply, hormone supply and response

29
Q

What is survival and development of follicles driven by?

A

FSH and LH

30
Q

Describe how FSH and LH recruit follicles

A
  • follicles respond to FSH, less to LH
  • FSH drives follicular growth
  • become atretic without FSH
31
Q

What role does LH play in selection and dominance of follicles?

A

increases concentration and is more effective than FSH

32
Q

How do theca cells function?

A
  • contain LH receptors
  • cholesterol converted to androstenedione which is transferred to granulosa cells
33
Q

How do granulosa cells function?

A
  • FSH receptors
  • androstenedione converted to oestrodiol
34
Q

What are the different sizes of follicle in each species?

A
  • mare >3cm
  • cow 1-1.5cm
  • ewe 0.5-1cm
  • sow 0.5cm
  • bitch <0.25cm
  • queen <0.25cm
35
Q

How many oocytes are prepared for ovulation in each species?

A
  • mare, cow 1-2
  • ewe 1-3
  • sow 4-20
  • bitch, queen 8-10
36
Q

What determines number of oocytes ovulated?

A

whether the species is monotocous

37
Q

What triggers ovulation?

A

preovulatory LH surge

38
Q

How does the LH surge trigger ovulation?

A
  • increased blood flow to follicle and ovary
  • ovarian smooth muscle contractions
  • connective tissue destruction
39
Q

Describe connective tissue destruction in ovulation

A
  • tunica albuginea - sits over surface of ovary/ovulation fossa
  • weakens wall coupled with increased pressure from follicle - leads to rupture
  • follicular fluid secreted along with secondary oocyte which washes into infundibulum
  • ovum waits in ampulla and if fertilized - enters uterus via utero-tubular function in isthmus
40
Q

Describe what happens to the empty follilce post-ovulation

A
  • follicle wall collapses
  • theca, granulosa and connective cells mix
  • blood vessels rupture -> clot -> corpus haemorrhagicum
  • small blood clot in cavity
41
Q

Describe the formation of the corpus luteum

-

A
  • increases in size 3-5 days post ovulation
  • luteinisation of theca interna and granulosa cells
  • more structure to luteal tissue than early CH
  • active CL is red/orange/yellow
  • produces progesterone, precursor cholesterol
42
Q

Describe the breakdown of the corpus luteum

A
  • luteolysis breaks down CL to form corpus albicans
  • CL regresses and becomes smaller - no glandular tissue
  • scar tissue, light yellow-white
43
Q

Which waves occur whilst the CL is present?

A
  • recruitment
  • selection
  • dominance
  • atretic
  • NO ovulation
44
Q

Which hormone breaks down CL in order for the cycle to resume?

A

PGF2 alpha from the uterus

Reproductive Anatomy (10 decks)

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