Luteal phase wk 6 Flashcards
3 major events of the luteal phase are: (think about the CL development during these)
- Luteinisation (CL formation)
- Progesterone secretion (CL function)
- Luteolysis (CL destruction)
- Luteal phase usually lasts for about 80% of the oestrus cycle –> apart from the dog and maybe cat who have weird cycles**
What occurs during luteinisation process:
- process of transformation from a follicle to a corpus luteum (CL). Follicle basement membrane begins to break down
- at ovulation: follicular fluid volume decreases/reduced, walls of follicle fold in and follicle collapses on itself. Blood clot forms (corpus haemorrhagicum, due to ruptured blood vessels). Theca and granulosa cells mix.
- 2-3 days post ovulation - where we have full function of the CL –> cells are now now large luteal cells (granulosa) and small luteal cells (theca), and start secreting P4
Why does the CL increase in size during the luteal phase?
- Due to increased VOLUME of large luteal cells
- Increase NUMBER of small luteal cells
Why does the CL capacity dependent on vascularisation?
- Nutrition/energy/oxygen supply
HORMONES –> apart of the HPG axis and need vascular for hormone transport
What is the major function of the corpus luteum?
To produce progesterone:
→ like other steroids, requires cholesterol
→ LH at basal levels is required!
Hormones:
- LH helps with progesterone
- FSH drives development of new follicular waves → still occurs in Luteal phase just won’t get to ovulation stage**
What are the 4 different actions of progesterone? Note: think about the role of progesterone and what this would mean for mammary, endometrium, myometrium and brain:
Progesterone = pregnancy.
- Mammary glands - promotes development
- endometrium - promotes gland development, promotes gland secretion
- myometrium (muscle layer in uterus)- decreases uterine tone (Contractions)
- Brain - inhibits receptive behaviours for mating by progesterone
What is luteolysis and when does it occur?
- Occurs when female is not pregnant
- luteolysis is the breakdown of corpus luteum. Caused by
- drop in progesterone
- degeneration of CL tissue
What is the role of oxytocin in luteolysis? (how does it causes luteolysis in CL)
- endometrium develops oxytocin receptors, and CL secretes oxytocin
- oxytocin causes endometrial production of prostaglandin F2a
- → positive feedback between oxytocin and PGF2a
- → luteolysis cascade is triggered in the CL
What happens to the HPG axis after luteolysis? (think about process all the way to ovulation*)
- progesterone decreases
- → GnRH would increase because we have removed progesterone → this usually has negative feedback on HPG axis
- → gonadotropins INCREASE then
- → oestrogen increases, which will have POSITIVE feedback on HPG axis → SURGE of GnRH → LH to SURGE → OVULATION
What happens to the CL is the female is pregnant?
- CL will remain for development of foetus
- varies depending on species → either placenta will take over P4 production later in pregnancy
- OR Cl remains functional for the whole pregnancy
Luteal phase in the cow: length and CL development
- about 17 days
- CL is very large and distinct, often orangey/yellow
- during luteolysis CL becomes very pale yellow structure
- Cow is pretty ‘normal’ in terms of hormonal actions
Luteal phase in the sheep/ewe
- about 15 days
- relatively large and distinct CL, pink/red colour not yellow
- pale pink structure in luteolysis
- P4 fair bit lower than in cattle
Luteal phase in horse/mare
- about 15 days
- large distinct CL, pink/red in colour but can’t palpate* → use ultrasound
- during luteolysis CL becomes pale pink
Luteal phase in pigs (Sow)
- about 15 days
- many distinct CLs, pink/red in colour
- become pale pink/yellow in luteolysis
- very high P4 concentrations with more steady rise/less plateau during luteolysis → more slow rise the whole time then drops of pretty quickly in luteolysis
What would happen if we gave exogenous progesterone before the LH surge in females?
- Atresia of the dominant follicle (stopping the follicle from ovulating)
- all about the action of progesterone on HPG axis → for follicle to ovulate, needs to have the LH surge to dominate. So if we provide progesterone, we are slamming it with negative feedback thus limit LH production in the end
