The oestrous cycle Flashcards
What are examples of glycoprotein hormones?
- FSH (gonadotrophin)
- LH (gonadotrophin)
- inhibin
What hormone affects FHS and LH?
- GnRH
glycoprotein hormones travel where to affect what?
- travel down to the gonads and affect oestrogen and testosterone
What is an example of a peptide hormone and where is it produced?
- GnRH
- produced in the hypothalamus
What hormone acts on GnRH?
- melatonin
What hormone is an example of an amine hormone?
- melatonin
What does Melatonin do?
- links daylight hours with reproductive control
What type of breeder are ewes?
- seasonally polyoestrous so have continuous cycles of oestrous and will ovulate without presence of ram
- they are short day breeders
What is an example of an eicosanoids hormone?
- prostaglandins
- PGF2 alpha
- PGE2
What are examples of gonadal steroids?
- progestogens (e.g. progesterone; P4)
- testosterone
- oestrogens (oestradiol; E2)
What is neuropeptide (GnRH) synthesized by and how is it secreted?
- synthesised by hypothalamus neurones
- secreted in pulses
Neuropeptide (GnRH) secretion is controlled by what hormone?
- secretion is controlled melatonin
How is melatonin controlled in the ewe?
- 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
As day length gets shorter what happens to melatonin?
- it increases
What happens when there is an increase in melatonin in the ewe?
- increase in melatonin is sent to hypothalamus to secrete more GnRH
In seasonally polyoestrous species what is light detected by and what’s does this control?
- light is detected by the pineal gland and controls melatonin secretion and thus GnRH
In breeding season GnRH pulse frequency controls what?
- controls whether female is in heat (oestrus) or between heat periods (dioestrus)
When does GnRH increase and when does it decrease?
- Increases close to ovulation
- decreases in-between period of ovulation
- creates a wave like pattern
How is GnRH pulse frequency controlled?
- controlled by feedback from gonads (P4 and E2) - ovary
Where are nerve impulses from the hypothalamus directed to produce more GnRH?
- the pituitary stork
In males what is GnRH frequency like in breeding season?
- remains basal
What is the function of GnRH?
- stimulates gonadotrophin secretion from anterior pituitary
What part of the oestrous cycle is progesterone dominant in?
- dominant during mid part of cycle which feedback onto hypothalamus and prevents surge of GnRH
What happens to GnRH when progesterone falls?
- GnRH is allowed to surge
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
What does the tonic centre do?
- releases small episodes of GnRH in a pulsatile fashion
- this episodic release is continuous throughout reproductive life
How many times does FSH rise in the ewes oestrous cycle?
- 3 times
How long is a ewes oestrous cycle?
- 17- day cycle
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
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
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
What are FSH and LH?
- short glycoproteins with alpha and beta subunits
If FSH and LH both have alpha and beta subunits what is the difference?
- the beta chain is different and effects function
Where are LH and FSH synthesied?
- synthesised in anterior pituitary
How are LH and FSH secreted?
- secreted in pulses into circulation to act on an ovary
What does a surge in LH stimulate?
- stimulates ovulation
- so frequency and amplitude are important
What is the general level of LH throughout the cycle?
- stays at basal level for vast majority of cycle
What does every steroid hormone start as?
- cholesterol
What does cholesterol have to be converted into?
- pregnenolone
- does this by removing carbon rings from 27 to 21
What is pregnanolone converted into?
In what organ would this process stop here?
- progesterone
- in corpus luteum this is where the process would end
Where is progesterone synthesis and secretion prominent in?
- prominent in ovary from luteal cells of corpus luteum
What is progesterone converted into and where would this process stop?
- converted into testosterone
- this process would stop in the testes
Where is testosterone synthesis and secretion prominent?
- prominent at Leydig cells in testes and theca cells in the ovary
What is testosterone converted into?
- converted into oestradiol
Where is oestradiol synthesis and secretion prominent?
- prominent in the ovary by granulosa cells of growing follicle
What hormone is responsible for mating hormones in the female?
- oestrogen
In the dominant follicular phase secretion in developing follicles is controlled by what?
- by FSH and LH
What do theca cells do?
- detect LH to stimulate testosterone production
What do granulosa cells do?
- detect FSH which stimulate testosterone conversion to E2
As the follicle grows what is secreted?
- more E2 secreted until ovulation
What are theca and granulosa cells known as?
- two cell, two gonadotrophin model
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
In the female oestradiol affects the reproductive tract - How?
- increases blood flow
- uterine oedema
- development of uterine glands
- mucus secretion
What phase is progesterone dominant in and what is it secreted by?
- dominant in luteal phase
- secreted by corpus luteum
How does progesterone prepare the uterus for pregnancy?
- increases uterine tone (floppy to toned) so its ready to accept fertilised embryo
- gland secretion of uterine milk
- cervical tightening
- mammary development
During the luteal phase negative feedback on the hypothalamus and pituitary inhibits what hormones?
- inhibits GnRH release and prevents LH increasing
What hormone is secreted from the uterine endometrium to the ovary if there is no pregnancy
- pulsatile
- signals to have another ovulation
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
Why cant you take a blood test for PGF2a?
- because its metabolised quickly in the blood
What is measured instead of PGF2a?
- PGFM
