Initiation of parturition Flashcards
What are the 3 stages of parturition?
- initiation of myometrial contraction
- expulsion of the fetus
- expulsion of the fetal membranes
Describe the HPA axis
What is the role of fetal cortisol?
Reduces progesterone levels:
- removes block on myometrial contractions
- repro tract secretions increase
Stimulates uterine prostaglandin production:
- causes uterine contraction
- acts on ovary to cause luteolysis
- relaxin produced changes structure of cervix
How is parturition initated?
Describe the neuro-hormonal reflex causing oxytocin release
Increased rpessure on cervix activates pressure sensitive neurons
Relay afferent info to hypothalamus
Neural input to posterior pituitary => oxytocin release
What is the mechanism of myometrial contractions
Ca binds to calmodulin
Calmodulin interacts and activates with MLCK
MLCK causes reduction of ATP to ADP + inorganic phosphate
Phosphate is added to head MLC (myosin light chains)
Change in myosin -> binds to actin -> contraction
What is the role of gap junctions in coordination of myometrial contractility?
Low resistance pathways between myometrial cells allows uterus to act as electrical syncytium
Increase in density and size towards parturition
Presence and permeability is under steroid and prostaglanding control
How is myometrial contraction regulation?
Oxytocin - increases force, duration and frquency of contractions
Prostaglandins:
- isoforms locally produced and act locally (from arachadonic acid)
- PGF2a => contraction
- PGI2 => relaxation
- PGE2 => cervical softening
Neural input:
- autonomic NS via pelvic plexus innervates endo/myometrium
- a adrenergic receptors => contraction
- b adrengergic receptors =< relaxation
What are the methods of terminating pregnancy?
Induce luteolysis:
- PGF2a
- remove luteotrophic support (prolactin inhibitors)
Remove progesterone support:
- inhibit synthesis
- inhibit receptor actions
Induce premature parturition
Why might you induce parturition?
Predetermine parturition and better animal car
Industry advantage
Reduce late calving to ensure it coincides with good pasture
Reduce risk of oversized foetus
Disease or illness of dam or offspring
history of high-risk pregnancy
How can you induce parturition?
Glucocorticoids - mimic fetal HPA
Prostaglandins - induce luteolysis and contractions
Oxytocin - cause contractions
What is the risk in inducing parturition?
Fetal immaturity => reduced survival
important in foals as critical maturation is 24-48hrs before birth
Why might you accelerate parturition?
uterine inertia or haemorrhage
remove abdnormal uterine product
retain placenta
How does oxytocin accelerate parturition and what are the risks?
How can PGF2a agonists be used to accelerate parturition and what are the risks?
Why might you reduce or prevent myometrial contractions?
How can you reduce or prevent myometrial contractions?
