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Ovarian function and control Flashcards

1
Q

What are the different stages of follicle?

A
  • Primordial
  • Priimary
  • Secondary
  • Tertiary/antral
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2
Q

Describe the structure and function of follicles

A
  • Oocyte maturation
  • Fluid filled
  • Secretes oestradiol
  • Multiple stages of development with different morphologies
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3
Q

Describe the structure and function of the corpus luteum

A
  • Highly vascularised
  • Transient endocrine gland
  • Solid
  • Progesterone production
  • Several inches in size, takes over most of ovary when present
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4
Q

What are the key steps in the formation of follicles?

A
  • Recruitment of follicular cells
  • Early follicular growth
  • Oocyte changes
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5
Q

Describe the recruitment of follicular cells

A
  • Granulosa cells form primordial follicle
  • Form cohorts/”egg nests”
  • Make up a reservoir
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6
Q

Describe early follicular growth

A
  • Local ovarian growth stimulated by IGFs, BMP
  • Many oocyte derived
  • Gonadotrophin independent
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7
Q

Describe the oocyte changes in follicular development

A
  • Increases cytoplasmic volume
  • Formation of zona pellucida
  • Communication via gap junctions
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8
Q

Describe primordial follicles

A
  • Recruitment of granulosa cells (flattened)

- Single layer of flattened granulosa cells

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9
Q

Describe the resting primary follicles

A
  • Act as reserves
  • Develop into secondary follicles
  • Granulosa proliferation occurs (cuboidal now)
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10
Q

Describe the secondary follicles

A
  • Surrounded by granulosa cells (multiple layers)
  • Zona pellucids present
  • Basement membrane forms
  • Recruitment of theca cells (originaly stromal cells)
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11
Q

Describe the antral maturing follicles

A
  • Escape influence of granulosa cells and resume meiosis
  • Develop in follicular waves
  • Fluid accumulation
  • Recruitment, selection and dominant antral follicles
  • Go through these stages quickly compared to rest of development
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12
Q

Describe follicle recruitment

A
  • Initiated by FSH wave
  • Cohort of small antral follicles (10-20) start to develop
  • Secrete small amount of oestradiol
  • Occurs in luteal and follicular phase
  • Some undergo atresia
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13
Q

Describe follicle selection

A
  • Dependent on FSH for support
  • Produce inhibin and oestradiol
  • Negative feedback on pituitary gland, supprsing only FSH
  • Become LH dependent
  • Some undergo atresia
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14
Q

Describe follicle dominance

A
  • Transition from FSH to LH depenedence
  • LH receptors appear in granulosa cells
  • Increased oestradiol and inhibin production = inhibits growht of other follicles
  • Growth 1mm/day in cow, >3mm/day in horse
  • Remain for ~6 days
  • ovulate or undergo atresia depending on whether progesterone falls
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15
Q

Describe the hormone levels in follicular recruitment

A
  • High FSH
  • Lower LH
  • Lower oestradiol from ovary back to surge centre
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16
Q

Describe the hormone levels in follicular selection

A
  • Increasing inhibin from ovary
  • Decreasing FSH
  • Increasing LH
  • Increasing oestradiol from ovary back to surge centre
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17
Q

Describe the hormone levels in follicular dominance

A
  • High inhibin from ovary
  • Low FSH
  • High LH (LH dependent)
  • Very high oestradiol back to surge centre
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18
Q

What is the effect of progesterone on follicular dominance?

A
  • No ovulation in presence of progesterone

- Dominant follicle will undergo atresia

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19
Q

How many follicular waves are seen in the cow?

A

3, first 2 end in atresia, last ends in ovulation

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20
Q

What is meant by the follicular wave?

A

The wave-like pattern of follicle development, i.e. will develop all the way to dominant follicle then become atretic repeated a few times before ovulation occurs

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21
Q

What cells are involved in the production of oestradiol from the ovary?

A

Theca and granulosa cells

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22
Q

What stimulates the production of oestradiol?

A

FSH and LH

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23
Q

What is the key enzyme involved in oestradiol production?

A

Aromatase

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24
Q

What receptors are found on the theca and granulosa cells?

A
  • Theca: LH

- Granulosa: FSH

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25
Q

Describe the process of oestradiol production in the ovary

A
  • LH binds to receptors on LH cells
  • Stimulates production of enzymes producing testosterone
  • Testosterone to granulosa cells
  • When FSH binds, enzymatic cascade that converts testosterone to oestradiol
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26
Q

Outline the process of oogenesis

A
  • Primordial germ cells originate from hindgut
  • Proliferate by mitosis
  • first migrate to genital ridge, massive mitosis to form primary oocytes, then into meiosis
  • Arrest at prophase I until birth
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27
Q

Describe oocyte maturation

A
  • After ovulation
  • Cytoplasmic maturation takes place in preparation for embryo development, need RNA and organelles
  • Nuclear maturation stimulated by LH surge, completion of meiosis I
  • Meiosis II arrested until fertilisation leads to influx of Ca2+
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28
Q

What is ovulation?

A

The release of the oocyte

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29
Q

Where does ovulation occur?

A

Over the entire surface of the ovary, except mare where only occurs from ovulation fossa

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30
Q

What initiates ovulation?

A

Th LH surge, which is stimualted by oestradiol in the absence of progesterone

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31
Q

When does the LH surge occur?

A
  • Around the start of oestrus in cow, sheep, pig and dog

- Gradual increase in LH during oestrus in mares

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32
Q

What is the LH surge to ovulation interval in cows?

A

24-30 hours after LH surge

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33
Q

What is the LH surge to ovulation interval in mares?

A

LH levels elevated 5-6 days around ovulation

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34
Q

What is the LH surge to ovulation interval in dogs?

A

Variable, 24-96 hours after LH surge

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35
Q

Describe the ovulation event

A
  • High LH leads to fluid accumulation in maturing follicles, increased pressure
  • Surface connective tissue of ovary weakened by increased synthesis of collagenase
  • Ovarian smooth muscle cells contract, blood flow increases, local fluid accumulates
  • Follicular wall bursts
  • Oocyte and granuloma cells released from GC anchor point
  • Oocyte carried with follicular fluid into peritoneal cavity
  • Captured by fimbraie of infundibulum
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36
Q

Describe spontaneous ovulation

A
  • Hormone induced
  • Reduced production of progesterone from CL due to luteolysis
  • Increased follicular dvelopment
  • Oestradiol in absence of progesterone leading to LH surge
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37
Q

Describe induced ovulation

A
  • Can be induced by coitus e.g. cats
  • Single act of intercourse leads to LH surge in cat
  • Sensory stimulation stimulates surge centre
  • Multiple copulations leads to better responding LH surge
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38
Q

Describe the formation of the CL

A
  • Basement membrane breakdown
  • Lutenisation and migration
  • Granulosa avascular) become large luteal cells (hypertrophy)
  • Theca cells form small luteal cells (proliferation)
  • Rapid proliferation and hypertrophy of blood vessels when basement membrane breaks down
  • Intense angiogenesis
  • Steroidogenesis switch and increase (oestradiol to progesterone)
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39
Q

What are the different stages of the corpus luteum?

A
  • Corpus haemorrhagicum (early)
  • Corpus luteum (main one)
  • Corpus albicans (late, regressing)
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40
Q

What hormones support the growth and function of the CL?

A
  • LH
  • Prolactin in some species (rodents)
  • Other modulatory hormones: IGF-I, GH, PGE2
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41
Q

What cells of the CL produce the majority of progesterone?

A

Large luteal cells

42
Q

What stimulates the production of progesterone?

A

LH (small luteal cells only)

43
Q

What is the key regulatory step in progesterone production?

A
  • Transfer of cholesterol to mitochondria

- Steroid acute regulatory factor

44
Q

Describe luteal development in the bitch

A
  • Pre-ovulatory lutenisation leads to earlier progesterone rise
  • Thick wall (hypertrphy) and granulosa folds
  • No follicular collapse
  • Central luteal cavity
45
Q

What is the regression of the CL called?

A

Luteolysis

46
Q

When is luteolysis induced?

A

Following ovulation in the absence of an embryo

47
Q

What does luteolysis enable?

A
  • Pre-ovulatory follicular development allowing ovulation to occur
  • Return to oestrus
48
Q

What is the key luteolytic hormone?

A

Prostaglandin F2 alpha (PGF2a)

49
Q

How is endometrial PGF2a release stimulated?

A
  • Luteal oxytocin stimulates oxytocin reeceptor in endometrium
  • Release of PGF2a
  • Positive feedback
    loop: luteolysis stimulates more release of oxytocin
50
Q

Describe the utero-ovarian vascular counter-current system

A
  • PGF2a from uterus to ipsilateral ovary through vascular counter-current exchange
  • From endometrium enters uterine vein, then to ovarian artery (diffusion in counter current)
  • PGF2a delivered in high conc while bypassing general circulation
51
Q

What is the importance of the utero-ovarian vascular counter current system?

A
  • 98-99% PGF2a denatured by one passage through lungs
  • Need to maintain high levels
  • Is not present in mare as PGF2a not metabolised to same degree
52
Q

Describe the structural component of the luteolysis mechanism

A
  • Reduced blood flow
  • Increase in macrophages and lymphocytes
  • Apoptosis and tissue resorption
  • Corpus albicans
53
Q

Describe the functional component of the luteolysis mechanism

A
  • Mediated by down-regulation of steroidogenic enzymes

- Rapid fall in progesterone

54
Q

What is a key trigger for luteolysis?

A
  • Up-regulation of oxytocin receptors in the endometrium (before fall in progesterone)
  • Progesterone loses ability to suppress the expression of oxytocin receptors
55
Q

Describe PGF receptor expression on the CL

A
  • Not always expressed
  • CL only responds at certain times
  • Can induce luteolysis in these times with exogenous PGF2a
56
Q

What occurs during metoestrus?

A
  • Cells of follicle transformed into luteal cells
  • Form CL
  • P4 increasing
57
Q

What occurs during dioestrus?

A

Fully functional CL and maximal P4 secretion

58
Q

What is the lenght of the oestrus cycle in the

a. ewe
b. cow
c. mare
d. sow
e. bitch

A

a. 17 days
b. 21 days
c. 21 days
d. 21 days
e. 6-7 months

59
Q

How long is oestrus in the

a. ewe
b. cow
c. mare
d. sow
e. bitch

A

a. 24-36 hrs
b. 8 hours
d. 4-8 days
c. 2-3 days
e. 7-14 days

60
Q

How long is the follicular phase in the

a. ewe
b. cow
c. mare
d. sow
e. bitch

A

a. 4 days
b. 1 day
c. 6-10 days
d. 5-8 days
e. 18 days

61
Q

How big is the ovulatory follicle in

a. ewe
b. cow
c. mare
d. sow
e. bitch

A

a. 6-8mm
b. 9-13mm
c. 10-15mm
d. 8-10mm
e. 4-13 mm

62
Q

How many follicles are ovulated in the

a. ewe
b. cow
c. mare
d. sow
e. bitch

A

a. 2-3
b. 1
c. 1
d. 30-50
e. 2-15

63
Q

How long is the luteal phase in the

a. ewe
b. cow
c. mare
d. sow
e. bitch

A

a. 13 days
b. 19-20 days
c. 14 days
d. 15 days
e. 65 days

64
Q

How big is the mature CL in the

a. ewe
b. cow
c. mare
d. sow
e. bitch

A

a. 7-9mm
b. 20-25mm
c. 40-50mm
d. 10-12mm
e. 6-7mm

65
Q

Define the oestrus cycle

A

The repetitive patterns of hormones and behaviour which lead to ovulation

66
Q

How can oestrus be described?

A
  • Behaviour
  • Hormones
  • State of ovaries (follicle or CL)
67
Q

What is pro-oestrus?

A

The phase immediately before oestrus

68
Q

In what order do the phases of the oestrus cyce occur?

A
  • Pro-oestrus
  • Oestrus
  • Met-oestrus
  • Dioestrus
69
Q

Describe the behaviour of the oestrus female

A
  • Receptive to male
  • High levels of oestrogens
  • Will stand to be covered
  • Clitoral winking
70
Q

Describe the behaviour of the dioestrus female

A
  • Rejects male (can be violent)

- High levels of progesterone

71
Q

When is progesterone high and when is it low?

A
  • Very low in oestrus

- Once ovulation occurs, CLs produce lots of progesterone, high in dioestrus

72
Q

When is oestrogen high and when is it low?

A
  • High in oestrus

- Declines following ovulation (to baseline)

73
Q

What occurs at day 0 of the oestrus cycle?

74
Q

What is the function of the gonadotrophins?

A
  • Stimulate development of the gonads

- FSH and LH

75
Q

What stages of the oestrus cycle make up the luteal phase?

A

Metoestrus and dioestrus

76
Q

What stages of the oestrus cycle make up the follicular phase?

A

Pro-oestrus and oestrus

77
Q

What happens in the follicular phase?

A
  • Ovarian follicles mature
  • Secrete increasing concentrations of oestradiol into blood
  • Oestrus behaviour
  • High oestrogen
78
Q

What happens in the luteal phase?

A
  • Ovarian follicles ovulate to produce CLs
  • CLs secrete progesterone into blood
  • Ends with luteolysis by PGF2a
  • Follicles continue to develop in this stage but fail to ovulate (follicular waves)
  • High progesterone
79
Q

What are the actions of oestrogen?

A
  • Behaviour for mating
  • Prepare external genitalia and vagina for mating (increased blood flow)
  • Increase mucus production in the cervical glands
  • Bleeding in dogs and cows but not mestruation
  • Stimulates follicular growth and maturation
  • Prepares uterine environment for sperm transport and implantation of oocyte
  • Growth and development of mammary tissue
  • Preparation of uterus for parturition
80
Q

What are the functions of progesterone?

A
  • Increase secretion by uterine glands
  • Prepares uterus for zygote
  • Behaviour to reject male
  • Maintenance of pregnancy
81
Q

Give a brief summary of the oestrus cycle

A
  • Elevation of oestradiol and FSH = follicular development (follciular phase) and oestrus behaviour
  • LH surge induces ovulation
  • CL formed, secretes progesterone = luteal phase
  • Female behaviour changes to reject male as enters dioestrus
  • At end of dioestrus in absence of pregnancy, CL lysed by PGF2a
  • Progesterone levels decline, female accepts male, follicualr development begins again
82
Q

What hormonal changes occur if the animal is pregnant?

A
  • Conceptus releases maternal recognition of pregnancy signal in mid-dioestrus
  • Prevents luteolysis
  • Maintains high progesterone
83
Q

What is the function of the progesterone produced by the CL in pregnancy?

A
  • Keeps cervix closed

- Alows pregnancy to develop until placenta takes over progesterone production

84
Q

Define polyoestrus

A

Multiple cycles throughout the year e.g. cow, pig, rodents

85
Q

Define seasonal polyoestrus

A

Multiple cycles during one season

- Can be long or short day

86
Q

Give examples of long vs short day breeders

A
  • Long: mares, in spring

- Short: ewes, in autumn

87
Q

Define monooestrus

A

Infrequent cycles, independent of season, 1 or 2 cycles throughout year
e.g. bitch

88
Q

Give an example of induced breeders

89
Q

Describe the oestrus cycles of seasonal polyoestrus breeders

A
  • Show regular cycles in season
  • When season changes, undergo transition phase where hormones and ovaries change due to daylight
  • Prolonged period of anoestrus
90
Q

What is the effect of seasonal breeding?

A

The offspring are born at times where the conditions are favourable

91
Q

How come mares and ewes both give birth in spring?

A
  • Mare has 11 month gestation so conception in spring means will be bron in spring of next year
  • Ewe has shorter gestation so conception in autumn means birth in spring
92
Q

What controls seasonality?

A

Length of daylight

93
Q

Explain how light controls seasonality

A
  • Light detected by retina
  • Signal to pineal gland
  • Melatonin release acts on hypothalamic centre (specific to type of breeder)
  • Either stimulates or inhibits release of gonadotrophins
  • Release of oestrogen or P4 accordingly
  • Direct effect on uterus
94
Q

For the mare, give the

  • type of cycling
  • length of oestrus
  • lenght of dioestrus
  • total cycle length
  • timing of ovulation
A
  • Seasonal polyoestrus, long day
  • Oestrus: 6 days
  • Dioestrus: 15 days
  • Total lenght: 21-23 days
  • Ovulation: last day of oestrus/before end of oestrus
95
Q

For the cow, give the

  • type of cycling
  • length of oestrus
  • lenght of dioestrus
  • total cycle length
  • timing of ovulation
A
  • Polyoestrus
  • Oestrus: 8 hours
  • Dioestrus: 19-20 days
  • Total cycle length: 18-24 days
  • Ovulation: 12 hours after the end of oestrus (24-32 hours after onset)
96
Q

For the ewe, give tha

  • type of cycling
  • length of oestrus
  • lenght of dioestrus
  • total cycle length
  • timing of ovulation
A
  • Seasonal polyoestrus (short day)
  • Oestrus: 30 hours
  • Dioestrus: 15-16 days
  • Total cycle length: 17 days
  • Ovulation occurs towards the end of oestrus
97
Q

For the sow, give the

  • type of cycling
  • length of oestrus
  • lenght of dioestrus
  • total cycle length
  • timing of ovulation
A
  • Polyoestrus
  • Oestrus: 53 hours
  • Dioestrus: 19 days
  • Total cycle length: 21 days
  • Ovulation around 35-45 hours after start of oestrus
98
Q

For the nanny, give the

  • type of cycling
  • length of oestrus
  • lenght of dioestrus
  • total cycle length
  • timing of ovulation
A
  • Seasonal polyoestrus, short day
  • Oestrus: 30-40 hours
  • Dioestrus: 20-21 days
  • Total cycle length: 21-22 days
  • Ovulation around 12-36 hours after the strt of oestrus
99
Q

For the bitch, give the

  • type of cycling
  • length of pro-oestrus
  • lenght of oestrus
  • timing of ovulation
  • length of metoestrus
  • length of anoestrus
  • length of interoestrus
A
  • Monooestrus
  • Prooestrus: 9 days
  • Oestrus: 9 days
  • Ovulation 1-2 days after onset of oestrus
  • Met-oestrus: 70-80 days if measured by CL regression, 130-140 days if measured by endometrial repair
  • Anoestrus: 3 months
  • Interoestrus: 7 months
100
Q

For the queen give the

  • type of cycling
  • length of oestrus
  • lenght of dioestrus
  • total cycle length
  • timing of ovulation
A
  • Seasonal polyoestrus, long day (March - Sept)
  • Oestrus: 7-10 days
  • Dioestrus: 10-14 days
  • Total cycle length: 21 days
  • Ovulation dependent on mating (induced ovulators)
101
Q

For the jill, give the

  • type of cycling
  • lenght of oestrus
  • total cycle length
  • timing of ovulation
A
  • Seasonal polyoestrus
  • Oestrus: if mated 14 days, if unmated 6 months or under
  • Induced ovulators, 30-40 hours after mating

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