Lecture 3 Flashcards
Define polyoestrus cycle
Uniform cycles throughout the year
Define seasonally polyestrus
Cluster of cycles in the year
Define Monoestrus
one cycle a year
Describe the oestrus cycle
- Begins with behavioural oestrus/ovulation
- Short follicular phase
- Long luteal phase
Describe the menstrual cycle
- Begins with menses
- Ovulation mid-cycle
- Longer than oestrus cycle
- Follicular phase = luteal phase
List the 4 stages of mammalian oestrous cycle
- Proestrus: ovulatory follicle development and increased oestradiol
- Oestrus: sexual receptivity and peak oestradion
- Metestrus: corpus lute formation and increased progesterone
- Diestrus: sustained luteal secretion of progesterone
Does the length of diestrus differ in pregnant and non-pregnant bitches
No
What are the 3 things needed for ovulation
- Decline in progesterone needed to allow development of pre-ovulatory follicles
- High levels of oestrogen needed for pre-ovulatory follicle to stimulate GnRH surge = LH surge
- Pre-ovulatory surge of LH needed to tigger ovulation
How does LH trigger ovulation?
Refer to diagram in lecture 3
Explain the formation of the corpus luteum
- During luteal phase of cycle from post-ovulatory follicle
- First forms corpus haemorrhagicum 1-3 days after ovulation
- Consists of large luteal cells and small luteal cells
What is the primary function of the corpus luteum
Secrete progesterone
Why is regression of the corpus luteum necessary in absence of successful pregnancy
allows another follicular phase and ovulation to occur –> elevated progesterone inhibits the LH surge
Why does Luteolysis occur
- Failure of luteotrophic support
- Production of luteolytic factors
What is the white/yellow scar called that remains after the luteolysis cell death
Corpus albicans
Where is luteolytic factors derived from (PGF2a)
Endometrium
What is the main luteolytic agent
Prostaglandin F2 alpha
How is prostaglandin F2a secreted from the endometrium
In pulses at 5 hour intervals and pass to the corpus luteum via a counter current system
Under what influences do oxytocin receptors develop?
progesterone and oestrogens
What stage does the corpus luteum form from
Metestrus
What does elevated progesterone inhibit
LH surge
What happens to the PGF2a secretion is there is a pregnancy
It is prevented by secretion of other stuff that bind to the receptors Primates: CG Ruminants: Interferon T Horses, pigs: Oestrogen Mice: prolactin
What is the production of PGF2a stimulated by
Secretion of oxytocin from the corpus luteum
Describe the process of luteolysis and oxytocin
Pituitary oxytocin acts on the endometrium -> PGF2a secreted -> Acts on the corpus luteum causing luteolysis -> this triggers luteal oxytocin which acts on the endometrium to cause further secretion of PGF2a
Explain how PGF2a inhibits progesterone and triggers luteolysis
PGF2a binds to specific receptor on the plasma membrane of luteal cells, the PGF2a receptor complex opens Ca++ channels so that Ca++ influx occurs. High intracellular Ca++ is though to cause apoptropic effects. The PGF2a receptor compxls also activated protein kinase-C which inhibits progesterone synthesis
