Endocrinology of partuition Flashcards
What are the three gradual stages of partuition?
1) initiation of myometrial contraction
2) expulsion of the foetus
3) expulsion of the foetal membranes
Parturition is initiated by?
Hormonal signals from the foetus.
What foetal hormone matures the foetus?
GLUCOCORTICOIDS
FOETAL CORTISOL
FOETAL STRESS
Foetal cortisol released by fetal stress does what?
Foetal cortisol is responsible for upregulating all the enzymes that convert progesterone to estradiol.
Why are glucocorticoids called glucocorticoids?
Because of their effects on glucose metabolism.
What are the hormonal stages of parturition?
- increasing foetal cortisol
- removal of progesterone block
- increased oestrogen
- increased prostaglandins
= parturition in most species.
What does ingestion of skunk cabbage by a pregnant mother do?
• produces a lamb that has a delayed labour due to absence of the hypophysial stalk and pituitary causing adrenal hypoplasia
This results in insufficiency as far as steroid production and metabolism is concerned
• Ultimately prolonged gestation as no fetal stress is produced.
Cyclopic lambs
What does foetal cortisol do?
Reduces progesterone levels so:
— Removal of block on myometrial contractions
— Reproductive tract secretions increase
Fetal cortisol also stimulates uterine prostaglandin production
— Causes uterine contraction
— Acts on the ovary and causes lysis of corpus
Iuteum
— Relaxin produced changes structure of cervix
(most species except cow) Allows for stretch
What is the neuro-hormonal reflex?
Increasing pressure on the cervix activates pressure
sensitive neurons that relay afferent information to
the hypothalamus (PVN) then neural input to the posterior pituitary stimulates oxytocin release.
What happens to gap junctions within the myometrium prior to parturition
Gap junctions change in density and size according to hormones. Can increase from 10 per cell to 450 per cell around partuition.
6 conexin monomers make 1 conexon.
What does oxytocin do with regards to partuition?
Increases force, duration and frequency of contractions (via inositol triphosphate)
What do prostaglandins do with regards to partuition?
Isoforms locally produced to act locally
- PGF2a = CONTRACTION
- PGi2a (prostacyclin) = RELAXATION
— PGE2 important in cervical softening
How does neural input impact on parturition?
Autonomic NS via pelvic plexus
innervates uterus ( endo/myometrium) through
alpha 1&2 and beta 1&2 adrenergic receptors
— alpha 1 - activation causes contraction
— beta 2- activation causes relaxation
(high progesterone increases the number of beta receptors)
Glucocorticoids are used as drugs before labour. What do they do?
Commonly used to induce abortion /parturition in late term gestation
Oxytocin is used as a drug during and after labour. What does it do?
Given to strengthen contractions and expel placenta / membranes. Why speed up labour? • uterine inertia or haemorrhage • remove abnormal uterine product • retained placenta (after parturition)
