Female endocrinology 2 Flashcards
What occurs in the luteal phase…? How can these events be categorised?
Follicular cells -> luteal cells
Dev. of CL & prod. of P4 (lutenisation)
Destruction of CL & resumption of follicular phase (luteolysis)
Categorised as events following ovulation
First part of the luteal phase? (Directly after ovulation)
metestrus
What occurs during metestrus…?
formation of CL (gradual increase in P4)
What phase follows metestrus?
diestrus
What occurs during diestrus…?
P4 dominating hormone produced by functioning CL
Thecal cells have receptors for… and produce…?
LH and produce testosterone
Granulosa cells have receptors for… and produce…?
FSH and produce oestrogen
In the pre-ovulatory follicle (oestrus), what happens to the basement membrane?
Starts to deteriorate allowing granulosa & thecal cells to contact each other (because of increased pressure build up within follicle - antrum)
What happens to corpus haemorrhagicum (CH) during ovulation…?
Follicular walls collapse due to deteriorated basement membrane
Local haemorrhage
Ruptured blood vessels
Gland is formed consisting of thecal & Granulosa cells & connective tissue -> (CL)
What does the corpus luteum (CL) consist of…?
Mix of large luteal cells (LLC - granulosa cells) & small luteal cells (SLC - thecal cells)
When does the CL begin to increase in size?
Day 3-5
What determines the amount of progesterone produced by the CL?
The maximum size of the CL
ie. the bigger the CL, the more P4 produced by it.
Luteal formation in the cow…? What happens to CL, LLCs, SLC…?
CL begins to increase in size until halfway thru Luteal phase
Hypertrophy of LLCs, Hyperplasia of SLCs, peak P4 production (diestrus), orange CL colour reflects high beta carotene
Functional capability of CL & progesterone production depends on…?
Number of functioning luteal cells
Degree of vascularisation within CL (hormone delivery)
Insufficient luteal function results in…?
Reduced ability of uterus to support pregnancy
Reproductive failure
How would you treat insufficient luteal function results in…?
Supplement with progesterone
Describe progesterone synthesis…?
- LDL-CHOL bind to membrane receptors -> 2. LH binds to LH receptor on membrane -> 3. activates protein kinase -> 4. CHOL moves into mitochondria -> 5. CHOL -> pregnenolone -> into cytoplasm -> preg -> progesterone -> out of cell to target tissue
Physiological effects of progesterone…?
Hypothalamus
- -ve feedback on GnRH
- supression of LH & FSH & oestrogen -> behaviour
Uterus
- glandular edometrium -> maximal secretion (in preparation for embryo…fetus…birth)
- Muscular myometrium (muscle layer within uterus) -> inhibition of motility (stop uterine contractions/still/calm)
Mammary gland
- alveolar development (ready for milk production at end of gestation)
Describe the events in luteolysis…
- disintegration of CL
- occurs near end of luteal phase (1-3 days)
- significant reduction of P4 production
- regulated by oxytocin, prog. & prostaglandin (PGF2alpha)
In sheep studies, what occurred to CL lifespan when uterus was 1. left intact, 2. underwent uterectomy, 3. partial uterectomy contralateral to CL, 4. partial uterectomy ipsilateral to CL?
- 15 - 17 d
- 148 d
- 15 - 17 d
- 35 d
THMessage from sheep uterectomy studies…?
Local circulation of PGE 2alpha important for proper CL destruction, if no PGE 2alpha released from uterus -> CL was NOT destructed
How does PGE 2alpha get to the ovary?
via a vascular counter current exchange system
PGF 2a produced by uterine endometrium -> uterine vein & lymph -> ovarian artery via passive diffusion -> ovary
What happens to PGF 2a in normal circulation?
denatured thru pulmonary system
Why is counter current mechanism important in the cow & sow?
As it allows adequate levels of PGF 2a to exert lytic effects directly on functional CL
When is PGF 2a effective on the CL in the cow & sow?
cow (5-6 days after ovulation)
sow (12-14 days after ovulation)
Why would exogenous PG be administered?
To artificially lyse CL to syncronise oestrus & induce parturition (eg. sheep to give birth to lamb)
What is oxytocin’s role in luteolysis…? Where is it produced & stored? How & when is it released?
Produced by luteal cells, stored in secretory granules until threshold is reached.
Released in pulsatile manner towards end of luteal phase -> causes release of PGF 2a from endometrial cells
Where & when do oxytocin receptors form?
Endometrial cells, 10-12 days after ovulation
What blocks formation of oxytocin receptors?
progesterone (P4)
Requirements for luteolysis in the cow…?
- presence of oxytocin receptors in endometrium
- presence of critical secretion of oxytocin via LLCs
- PGF synthesised by endometrium, released in pulsatile secretion & critical number of pulses required for luteolysis
- presence of PGF 2a receptors on CL
Events that occur after luteolysis…?
- Reduction of P4
- CL forms Corpus Albicans
- Macrophages & lymphocytes phagocytise damaged luteal cells
- New follicular dev. & recruitment of antral follicles
Main difference between luteolysis in humans/primates compared to other domestic breeds…?
- controlled by hypothalamus & ovary NOT uterus (not required)
- PGF 2a produced by ovary in response to oxytocin release from posterior pituitary
- reduction in P4 -> PGF 2a synthesis from endometrium of ovary -> endometrial vasoconstriction, necrosis & sloughing -> MENSES (discharge of blood & cellular debris)
What effects does exogenous progesterone have…?
- mimics the luteal phase (lengthen or reduce)
- provides -ve feedback on hypothalamus -> supress GnRH release
- suppress oestrus behaviour (horses)
- allows synchronisation of individuals -> in AI or ET programs
- contraceptive in humans -> block ovulation & minimise pregnancy
What is CIDR?
controlled internal drug release
How does synchronisation in cows work?
via CIDR (P4 as drug) inserted into vagina & releases P4 diffuses across vaginal mucosa -> blood stream -> suppresses GnRH, follicular dev. & ovulation eg. administer CIDR for 7 days to all cows then remove => all cows synchronised so that when [P4 plasma] levels fall -> PGF 2a can be injected -> luteolysis in all cows -> proestrus phase -> oestrus phase
How can synchronisation be achieved without CIDR?
By single injections with PGF2a between day 7 & 18 -> luteolysis -> oestrus 2-3 days later
(Days 1-7 the CL is refractory to PGF2a & will NOT respond)
When would a double injection (PGF2a) protocol be used?
When a small % of cows aren’t responsive to a single PGF2a dose (14 days apart) -> all cows should cycle together
What mechanism does PGF2a use to reach ovary in domestic spp.?
utero-ovarian vascular countercurrent diffusion system
Which hormone can be used to cause letenisation?
LH or hCG (has LH-like activity)
