The oestrous cycle Flashcards
1
Q
What are examples of glycoprotein hormones?
A
- FSH (gonadotrophin)
- LH (gonadotrophin)
- inhibin
2
Q
What hormone affects FHS and LH?
A
- GnRH
3
Q
glycoprotein hormones travel where to affect what?
A
- travel down to the gonads and affect oestrogen and testosterone
4
Q
What is an example of a peptide hormone and where is it produced?
A
- GnRH
- produced in the hypothalamus
5
Q
What hormone acts on GnRH?
A
- melatonin
6
Q
What hormone is an example of an amine hormone?
A
- melatonin
6
Q
What does Melatonin do?
A
- links daylight hours with reproductive control
7
Q
What type of breeder are ewes?
A
- seasonally polyoestrous so have continuous cycles of oestrous and will ovulate without presence of ram
- they are short day breeders
8
Q
What is an example of an eicosanoids hormone?
A
- prostaglandins
- PGF2 alpha
- PGE2
9
Q
What are examples of gonadal steroids?
A
- progestogens (e.g. progesterone; P4)
- testosterone
- oestrogens (oestradiol; E2)
10
Q
What is neuropeptide (GnRH) synthesized by and how is it secreted?
A
- synthesised by hypothalamus neurones
- secreted in pulses
11
Q
Neuropeptide (GnRH) secretion is controlled by what hormone?
A
- secretion is controlled melatonin
12
Q
How is melatonin controlled in the ewe?
A
- in the ewe melatonin is controlled by the detection of light by retina which sends nerve impulses to the pineal gland where melatonin is manufactured
13
Q
As day length gets shorter what happens to melatonin?
A
- it increases
14
Q
What happens when there is an increase in melatonin in the ewe?
A
- increase in melatonin is sent to hypothalamus to secrete more GnRH
15
Q
In seasonally polyoestrous species what gland is light detected by and what’s does this control?
A
- light is detected by the pineal gland and controls melatonin secretion and thus GnRH
16
Q
In breeding season GnRH pulse frequency controls what?
A
- controls whether female is in heat (oestrus) or between heat periods (dioestrus)
17
Q
When does GnRH increase and when does it decrease?
A
- Increases close to ovulation
- decreases in-between period of ovulation
- creates a wave like pattern
18
Q
How is GnRH pulse frequency controlled?
A
- controlled by feedback from gonads (P4 and E2) - ovary
19
Q
Where are nerve impulses from the hypothalamus directed to produce more GnRH?
A
- the pituitary stork
20
Q
In males what is GnRH frequency like in breeding season?
A
- remains basal
21
Q
What is the function of GnRH?
A
- stimulates gonadotrophin secretion from anterior pituitary
22
Q
What part of the oestrous cycle is progesterone dominant in?
A
- dominant during mid part of cycle which feedback onto hypothalamus and prevents surge of GnRH
23
Q
What happens to GnRH when progesterone falls?
A
- GnRH is allowed to surge
24
What does the surge centre do?
- the surge centre is sensitive to positive feedback and releases high amplitude, high frequency pluses of GnRH in a relatively short period after oestrogen reaches a threshold level
25
What does the tonic centre do?
- releases small episodes of GnRH in a pulsatile fashion
- this episodic release is continuous throughout reproductive life
26
How many times does FSH rise in the ewes oestrous cycle?
- 3 times
27
How long is a ewes oestrous cycle?
- 17- day cycle
28
What does FSH do?
- drives recruitment and development of follicles towards ovulation
- the bigger the follicle the more FSH receptors they have to get to ovulation
29
The first wave of follicles do not ovulate - Why and what happens to them afterwards?
- do not ovulate as there is no peak in LH
- enter a stage called atresia so they degenerate and disappear
30
The second peak of FSH and second period of follicular development coincide - what does this lead to?
- leads to development of a number of follicles and ovulation
31
What are FSH and LH?
- short glycoproteins with alpha and beta subunits
32
If FSH and LH both have alpha and beta subunits what is the difference?
- the beta chain is different and effects function
33
Where are LH and FSH synthesied?
- synthesised in anterior pituitary
34
How are LH and FSH secreted?
- secreted in pulses into circulation to act on an ovary
35
What does a surge in LH stimulate?
- stimulates ovulation
- so frequency and amplitude are important
36
What is the general level of LH throughout the cycle?
- stays at basal level for vast majority of cycle
37
What does every steroid hormone start as?
- cholesterol
38
What does cholesterol have to be converted into?
- pregnenolone
- does this by removing carbon rings from 27 to 21
39
What is pregnanolone converted into?
In what organ would this process stop here?
- progesterone
- in corpus luteum this is where the process would end
40
Where is progesterone synthesis and secretion prominent in?
- prominent in ovary from luteal cells of corpus luteum
41
What is progesterone converted into and where would this process stop?
- converted into testosterone
- this process would stop in the testes
42
Where is testosterone synthesis and secretion prominent?
- prominent at Leydig cells in testes and theca cells in the ovary
43
What is testosterone converted into?
- converted into oestradiol
44
Where is oestradiol synthesis and secretion prominent?
- prominent in the ovary by granulosa cells of growing follicle
45
What hormone is responsible for mating hormones in the female?
- oestrogen
46
In the dominant follicular phase secretion in developing follicles is controlled by what?
- by FSH and LH
47
What do theca cells do?
- detect LH to stimulate testosterone production
48
What do granulosa cells do?
- detect FSH which stimulate testosterone conversion to E2
49
As the follicle grows what is secreted?
- more E2 secreted until ovulation
50
What are theca and granulosa cells known as?
- two cell, two gonadotrophin model
51
Where is oestradiol detected and what does it influence?
- detected in brain centres
- to influence behaviour (signs if heat)
- acceptance of male by the female
- physical activity
- libido
52
In the female oestradiol affects the reproductive tract - How?
- increases blood flow
- uterine oedema
- development of uterine glands
- mucus secretion
53
What phase is progesterone dominant in and what is it secreted by?
- dominant in luteal phase
- secreted by corpus luteum
54
How does progesterone prepare the uterus and other areas for pregnancy?
- increases uterine tone (floppy to toned) so its ready to accept fertilised embryo
- gland secretion of uterine milk
- cervical tightening
- mammary development
55
During the luteal phase negative feedback on the hypothalamus and pituitary inhibits what hormones?
- inhibits GnRH release and prevents LH increasing
56
What hormone is secreted from the uterine endometrium to the ovary if there is no pregnancy
- pulsatile
- signals to have another ovulation
57
What is pulsatile detected by and what does it do?
- detected by luteal cells to cause luteolysis
- p4 concentrations decline as it will destroy the corpus luteum so it cannot produce anymore progesterone
58
Why cant you take a blood test for PGF2a?
- because its metabolised quickly in the blood
59
What is measured instead of PGF2a?
- PGFM
