Group 4 - Parturition and Post Party Period COMPLETE*** Flashcards
When does Parturition occur?
after the signal for birth is given by the foetus, when the foetus is sufficiently mature to survive the traumatic birthing experience
Which hormone primarily controls parturition?
foetal cortisol
What is the consequence of foetal cortisol causing a reduction in prostaglandin levels just prior to parturition?
it removes progesterones block on myometrial contractions
so the uterus can now contract
it removes progesterones block on oestradiol production
so oestradiol can stimulate increased secretions to lubricate the reproductive tract
oestradiol also increases myometrial contractions
What is the function of foetal cortisol? 2
it reduces progesterone concentration and increases oestradiol concentration
it stimulates uterine prostaglandin production
How does Foetal Cortisol achieve the switch from progesterone dominance to oestradiol dominance?
it increases the activity and expression of catalytic enzymes which convert progesterone to oestradiol
What is the consequence of foetal cortisol stimulating uterine prostaglandin production? 3
prostaglandin stimulates uterine contraction
it also acts on the ovary causing luteolysis and further reducing progesterone concentration
it stimulates the secretion of relaxin
which relaxes pelvic ligaments allowing them to stretch for cervical dilation
Explain how the foetus initially migrates towards the cervix 3
increasing concentrations of oestradiol stimulate myometrial contractions
increasing concentrations of prostaglandin stimulate myometrial contractions
this increases the pressure in the uterus and moves the foetus towards the cervix
Which reflex occurs once the Foetus applies pressure against the cervix?
- How does this reflex work? 6
neuroendocrine oxytocin reflex
the young assumes a streamline position and migrates towards the cervix
the pressure sensitive neurones in the cervix are activated when the foetus pushes against the cervix
this information is relayed to the hypothalamus
it stimulates the paraventricular nuclei
this stimulates the posterior pituitary gland to release oxytocin
oxytocin generates strong myometrial contractions
Describe the mechanism of myometrial contractions 10
each monocyte contains voltage gated calcium channels
calcium ions enter the cell through these channels
or in response to oxytocin binding to receptors on the surface
or in response to mechanical stretch as the uterus reaches its maximal size
the calcium ions bind to calmodulin inside the cell
the complex formed interacts with and activates the enzyme myosin light chain kinase
the enzyme can now convert ATP to ADP
the removed phosphate group is added to the head of the myosin light chain
this conformational change of myosin enables it to form actin-myosin cross bridges
and contract with increasing force
Which enzyme regulates myometrial contractions and how?
phosphatase can remove the phosphate group from the myosin light chain to inactivate myosin
Contractions must be highly co-ordinated in the uterus.
- Which structure enables contractions to be highly co-ordinated?
- where are they found? 2
- what do they do?
gap junctions
in clusters on the plasma membranes of myometrial cells
between individual myometrial cells
they allow the passage of ions and small molecules between cells
What is the role of oxytocin in parturition?
- how does it do this?
to increase the force, duration and frequency of contractions
via second messenger inositol triphosphate
How do prostaglandins regulate contractions? 4
isoforms of prostaglandins act locally
prostaglandin F2 alpha stimulates contractions
prostaglandin I2 stimulates relaxation
prostaglandin E2 is important for cervical softening
How does neural input regulate contractions? 4
the autonomic nervous system acts via the pelvic plexus
it innervates the uterus through specific receptors
the activation of alpha 1 receptors stimulates contraction
the activation of beta 2 receptors stimulates relaxation
As the uterus and cervix stretches, what does this do to enzyme COX2?
- What is the function of this enzyme?
- Hence, what effect does increased stretch have?
it increases the activity of COX2
to convert arachidonic acid into prostaglandins
since prostaglandins increase the number of oxytocin receptors it increases sensitivity to oxytocin
Pharmacology: Why would you want to terminate a pregnancy?
in response to unintended mating, severe risk to the dam, twin pregnancy, suspected foetal abnormality
Pharmacology: State 3 ways we can Terminate a pregnancy
induce luteolysis
remove progesterone support
induce premature parturition
Pharmacology: How can we induce luteolysis to terminate a pregnancy? 2
- How could you remove luteotrophic support in the bitch or queen?
- Why is this method variably successful?
using natural or synthetic prostaglandins
or by removing luteotrophic support
using prolactin inhibitors
success relies on the extent of reliance on the corpus luteum and timing of the lute-placental shift
Pharmacology: Aside from inducing luteolysis, how can we remove progesterone support to terminate a pregnancy? 2
by inhibiting progesterone synthesis
or inhibiting progesterone receptor action
Pharmacology: Why might you want to induce parturition? 5
reduce late calvings
ensures calving coincides with good pasture
reduces risk of foetal oversize
due to disease of dam or offspring
history of high risk pregnancy
Pharmacology: Generally, how is induced parturition achieved? 2
by mimicking normal pathways
using glucocorticoids, prostaglandins and oxytocin alone or in combination
Pharmacology: What is the risk of inducing parturition?
- when is this risk highest?
a premature foetus has reduced survival odds
for species where young develop late
Pharmacology: Why might you want to accelerate parturition? 3
due to uterine inertia
haemorrhage
retained placenta
Pharmacology: What drugs could you use to accelerate parturition?
oxytocin
prostaglandin f2 alpha agonist
glucocorticoids like dexamethasone
Pharmacology: Accelerating Parturition
- what is the risk when using Oxytocin? 2
could cause foetal death or uterine rupture if there is obstructive dystocia or if the cervix has not dilated
it could also cause unco-ordinated contractions
Pharmacology: Accelerating parturition
- What risks are associated with using prostaglandin F2 alpha to induce parturition?
could cause explosive expulsions and weak offspring
Pharmacology: When would you want to reduce or prevent contractions? 4
to delay delivery
to aid obstetrical manoeuvres
to relax the uterus for a C section
to replace a prolapsed uterus
Pharmacology: Give an example of a drug which can be used to reduce or prevent contractions
- what type of drug is this?
- What does it do?
clenbuterol
a beta 2 adrenergic agonist
it inhibits contractions and stimulates relaxation
Parturition: State the 3 stages of parturition
initiation of myometrial contractions
expulsion of foetus
expulsion of foetal membranes
Parturition: Describe the events occurring in stage 1 parturition 7
increase in foetal cortisol
increase in enzyme converting progesterone to oestradiol
progesterone concentration decreases
oestradiol concentration increase
prostaglandin concentration increases
elevated oestradiol increases tract secretions
decreasing progesterone removes the block on uterine contractions
Parturition: How does progesterone actually suppress myometrial contractions?
by increasing the expression of beta 2 adrenergic receptors
Parturition: In stage 1 of parturition, how does a foal and pup assume the disposition for expulsion? 2
- what about in a calf and lamb?
rotation from a ventral to dorsal position
extension of the forelimbs and head and neck
extension of the forelimbs and head and neck
