The oestrous cycle Part 2 Flashcards
Look at oestrous posters
What hormone is dominant in the follicular phase, what is it responsible for?
- E2 (oestradiol)
- 20% dominant throughout whole cycle
- responsible for receptive behaviour changes
What hormone is dominant in the luteal phase?
- P4 (progesterone)
- 80% dominant throughout cycle
What can the follicular phase be divided into?
- proestrus (E2) + oestrous (E2)
What can the luteal phase be divided into?
- metestrous (transitional) + dioestrous (P4 is at full production)
What is the follicular phase driving towards?
- ovulation
What happens during proestrus - phase 1?
- rapid follicular growth
- run up to ovulation
- dominant E2 secretion
- rapid regression of CL and declining P4 concentrations
What happens during oestrous - phase 2?
- female is receptive to male usually ovulates
- dominant E2 secretion
- LH surges causes ovulation and CL formation
- length of stage varies
How long is oestrous in the ewe?
- 1-2 days
How long is oestrous in a cow?
- 18hrs
Why is it more important to detect oestrous in cattle then ewes?
- in cows if you miss oestrous you need to wait another 21 days to AI
- not the same in ewes as they are exposed to ram
What happens during metestrous (phase 3)?
- usually 2-3 days long
- Cl formation, P4 secretion increases
- E2 concentrations decline
- metestrous bleeding in some species
What happens in dioestrus (phase 4)?
- CL is fully functioning
- dominant p4 secretion
- true dioestrus stage
- uterus prepares to receive embryo
How many follicular waves does a ewe have?
- 2 follicular waves
- 1st wave doesn’t ovulate
What does an LH surge result in?
- increased blood flow to ovary and dominant follicle = oedema and increased hydrostatic pressure
- follicular fluid volume increased
- breakdown of connective tissue in follicle wall
- leads to follicle bursting
How does oestrogen make the ewe more susceptible to the ram?
- chances the higher brain centres
What do rams perform to detect pheromones?
- rams detect pheromones by performing the flehmen reaction
What happens to granulosa and theca cells when the follicle ruptures and collapses?
- granulosa cells and theca cells implode inwards and change in structure to become new luteal cells - this process is called luteinisation
When does the corpus haemorrhagicum become the corpus luteum?
- once the luteal cells become fully functional
Granulosa cells luteinise to become what?
- large luteal cells
Theca cells luteinise to become what?
- small luteal cells
What do both large and small luteal cells secrete?
- progesterone
What do both large and small luteal cells have?
- have large vacuoles within the cytoplasm
- pack up progesterone and send it to surface in vacuoles
- also contain lipid droplets that contain cholesterol
What converts cholesterol to pregnenolone?
- LH from the anterior pituitary as it had a kinase enzyme that breaks the carbon rings
Progesterone reduces GnRH frequency to control what?
- controls LH and FSH secretion to keep them basal
What behaviour does progesterone inhibit?
- inhibits oestrous behaviour so the ewe is not susceptible to ram
Progesterone is detected by uterine endometrium to to what?
- increase secretions from uterine glands = if there is an embryo these glands secrete uterine milk nourishment
- affects uterine tone
