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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
Describe the process of oestradiol production in the ovary
- 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
26
Outline the process of oogenesis
- 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
27
Describe oocyte maturation
- 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+
28
What is ovulation?
The release of the oocyte
29
Where does ovulation occur?
Over the entire surface of the ovary, except mare where only occurs from ovulation fossa
30
What initiates ovulation?
Th LH surge, which is stimualted by oestradiol in the absence of progesterone
31
When does the LH surge occur?
- Around the start of oestrus in cow, sheep, pig and dog | - Gradual increase in LH during oestrus in mares
32
What is the LH surge to ovulation interval in cows?
24-30 hours after LH surge
33
What is the LH surge to ovulation interval in mares?
LH levels elevated 5-6 days around ovulation
34
What is the LH surge to ovulation interval in dogs?
Variable, 24-96 hours after LH surge
35
Describe the ovulation event
- 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
36
Describe spontaneous ovulation
- Hormone induced - Reduced production of progesterone from CL due to luteolysis - Increased follicular dvelopment - Oestradiol in absence of progesterone leading to LH surge
37
Describe induced ovulation
- 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
38
Describe the formation of the CL
- 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)
39
What are the different stages of the corpus luteum?
- Corpus haemorrhagicum (early) - Corpus luteum (main one) - Corpus albicans (late, regressing)
40
What hormones support the growth and function of the CL?
- LH - Prolactin in some species (rodents) - Other modulatory hormones: IGF-I, GH, PGE2
41
What cells of the CL produce the majority of progesterone?
Large luteal cells
42
What stimulates the production of progesterone?
LH (small luteal cells only)
43
What is the key regulatory step in progesterone production?
- Transfer of cholesterol to mitochondria | - Steroid acute regulatory factor
44
Describe luteal development in the bitch
- Pre-ovulatory lutenisation leads to earlier progesterone rise - Thick wall (hypertrphy) and granulosa folds - No follicular collapse - Central luteal cavity
45
What is the regression of the CL called?
Luteolysis
46
When is luteolysis induced?
Following ovulation in the absence of an embryo
47
What does luteolysis enable?
- Pre-ovulatory follicular development allowing ovulation to occur - Return to oestrus
48
What is the key luteolytic hormone?
Prostaglandin F2 alpha (PGF2a)
49
How is endometrial PGF2a release stimulated?
- Luteal oxytocin stimulates oxytocin reeceptor in endometrium - Release of PGF2a - Positive feedback loop: luteolysis stimulates more release of oxytocin
50
Describe the utero-ovarian vascular counter-current system
- 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
What is the importance of the utero-ovarian vascular counter current system?
- 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
Describe the structural component of the luteolysis mechanism
- Reduced blood flow - Increase in macrophages and lymphocytes - Apoptosis and tissue resorption - Corpus albicans
53
Describe the functional component of the luteolysis mechanism
- Mediated by down-regulation of steroidogenic enzymes | - Rapid fall in progesterone
54
What is a key trigger for luteolysis?
- Up-regulation of oxytocin receptors in the endometrium (before fall in progesterone) - Progesterone loses ability to suppress the expression of oxytocin receptors
55
Describe PGF receptor expression on the CL
- Not always expressed - CL only responds at certain times - Can induce luteolysis in these times with exogenous PGF2a
56
What occurs during metoestrus?
- Cells of follicle transformed into luteal cells - Form CL - P4 increasing
57
What occurs during dioestrus?
Fully functional CL and maximal P4 secretion
58
What is the lenght of the oestrus cycle in the a. ewe b. cow c. mare d. sow e. bitch
a. 17 days b. 21 days c. 21 days d. 21 days e. 6-7 months
59
How long is oestrus in the a. ewe b. cow c. mare d. sow e. bitch
a. 24-36 hrs b. 8 hours d. 4-8 days c. 2-3 days e. 7-14 days
60
How long is the follicular phase in the a. ewe b. cow c. mare d. sow e. bitch
a. 4 days b. 1 day c. 6-10 days d. 5-8 days e. 18 days
61
How big is the ovulatory follicle in a. ewe b. cow c. mare d. sow e. bitch
a. 6-8mm b. 9-13mm c. 10-15mm d. 8-10mm e. 4-13 mm
62
How many follicles are ovulated in the a. ewe b. cow c. mare d. sow e. bitch
a. 2-3 b. 1 c. 1 d. 30-50 e. 2-15
63
How long is the luteal phase in the a. ewe b. cow c. mare d. sow e. bitch
a. 13 days b. 19-20 days c. 14 days d. 15 days e. 65 days
64
How big is the mature CL in the a. ewe b. cow c. mare d. sow e. bitch
a. 7-9mm b. 20-25mm c. 40-50mm d. 10-12mm e. 6-7mm
65
Define the oestrus cycle
The repetitive patterns of hormones and behaviour which lead to ovulation
66
How can oestrus be described?
- Behaviour - Hormones - State of ovaries (follicle or CL)
67
What is pro-oestrus?
The phase immediately before oestrus
68
In what order do the phases of the oestrus cyce occur?
- Pro-oestrus - Oestrus - Met-oestrus - Dioestrus
69
Describe the behaviour of the oestrus female
- Receptive to male - High levels of oestrogens - Will stand to be covered - Clitoral winking
70
Describe the behaviour of the dioestrus female
- Rejects male (can be violent) | - High levels of progesterone
71
When is progesterone high and when is it low?
- Very low in oestrus | - Once ovulation occurs, CLs produce lots of progesterone, high in dioestrus
72
When is oestrogen high and when is it low?
- High in oestrus | - Declines following ovulation (to baseline)
73
What occurs at day 0 of the oestrus cycle?
Ovulation
74
What is the function of the gonadotrophins?
- Stimulate development of the gonads | - FSH and LH
75
What stages of the oestrus cycle make up the luteal phase?
Metoestrus and dioestrus
76
What stages of the oestrus cycle make up the follicular phase?
Pro-oestrus and oestrus
77
What happens in the follicular phase?
- Ovarian follicles mature - Secrete increasing concentrations of oestradiol into blood - Oestrus behaviour - High oestrogen
78
What happens in the luteal phase?
- 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
What are the actions of oestrogen?
- 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
What are the functions of progesterone?
- Increase secretion by uterine glands - Prepares uterus for zygote - Behaviour to reject male - Maintenance of pregnancy
81
Give a brief summary of the oestrus cycle
- 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
What hormonal changes occur if the animal is pregnant?
- Conceptus releases maternal recognition of pregnancy signal in mid-dioestrus - Prevents luteolysis - Maintains high progesterone
83
What is the function of the progesterone produced by the CL in pregnancy?
- Keeps cervix closed | - Alows pregnancy to develop until placenta takes over progesterone production
84
Define polyoestrus
Multiple cycles throughout the year e.g. cow, pig, rodents
85
Define seasonal polyoestrus
Multiple cycles during one season | - Can be long or short day
86
Give examples of long vs short day breeders
- Long: mares, in spring | - Short: ewes, in autumn
87
Define monooestrus
Infrequent cycles, independent of season, 1 or 2 cycles throughout year e.g. bitch
88
Give an example of induced breeders
Cats
89
Describe the oestrus cycles of seasonal polyoestrus breeders
- Show regular cycles in season - When season changes, undergo transition phase where hormones and ovaries change due to daylight - Prolonged period of anoestrus
90
What is the effect of seasonal breeding?
The offspring are born at times where the conditions are favourable
91
How come mares and ewes both give birth in spring?
- 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
What controls seasonality?
Length of daylight
93
Explain how light controls seasonality
- 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
For the mare, give the - type of cycling - length of oestrus - lenght of dioestrus - total cycle length - timing of ovulation
- 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
For the cow, give the - type of cycling - length of oestrus - lenght of dioestrus - total cycle length - timing of ovulation
- 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
For the ewe, give tha - type of cycling - length of oestrus - lenght of dioestrus - total cycle length - timing of ovulation
- Seasonal polyoestrus (short day) - Oestrus: 30 hours - Dioestrus: 15-16 days - Total cycle length: 17 days - Ovulation occurs towards the end of oestrus
97
For the sow, give the - type of cycling - length of oestrus - lenght of dioestrus - total cycle length - timing of ovulation
- Polyoestrus - Oestrus: 53 hours - Dioestrus: 19 days - Total cycle length: 21 days - Ovulation around 35-45 hours after start of oestrus
98
For the nanny, give the - type of cycling - length of oestrus - lenght of dioestrus - total cycle length - timing of ovulation
- 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
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
- 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
For the queen give the - type of cycling - length of oestrus - lenght of dioestrus - total cycle length - timing of ovulation
- 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
For the jill, give the - type of cycling - lenght of oestrus - total cycle length - timing of ovulation
- Seasonal polyoestrus - Oestrus: if mated 14 days, if unmated 6 months or under - Induced ovulators, 30-40 hours after mating

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