Later Foetal Development, Labour and Parturition Flashcards
In late foetal development, are the ventricles working in parallel or series?
parallel
Vascular shunts bypass what circulation to close at birth?
pulmonary and hepatic
Primitive air sacs form when?
20 weeks
Vascularisation of lungs begins when?
28 weeks
Surfactant production begins when?
20 weeks, upregulated towards term
How many hours a day does foetus spend making rapid respiratory movements in REM sleep?
1-4 hrs
When is endocrine pancreas become functional?
start of 2nd trimester
Functional insulin from when?
mid 2nd trimester
Liver glycogen in foetal development?
progressively deposited, accelerates towards term
Debris and bile acids from swallowed amniotic fluid forms?
meconium
When do foetal movements begin?
late 1st trimester
Foetal movements are detectable by the mother around when?
14 weeks
Stress response starts around?
18 weeks
Thalamus cortex connections forming from?
24 weeks
What state of consciousness in the foetus in during development?
mostly slow wave or REM sleep
Organ maturation is co-ordinated by?
fetal corticosteriods
The process of labour includes?
safe expulsion of foetus at correct time, expulsion of placenta and foetal membranes, period of resolution/healing to permit future reproductive events
Labour has the characteristics of?
pro inflammatory reaction (immune cell infiltration and inflammatory cytokine and prostagladin secretion
What happens in the first stage of labour?
contractions start, cervix dilation
What occurs in the latent and active phases of the first stage of labour?
latent: slow dilation to 2-3cm
active: rapid dilation to 10cm
What happens in the second stage of labour?
maximal myometrial contractions, delivery of the foetus
What happens in the third stage of labour?
delivery of the placenta, expulsion of foetal membranes, postpartum repair
Why does the cervix have high connective tissue content?
provides rigidity
stretch resistant
Describe the remodelling of the cervix.
Bundles of collagen fibres embedded in a proteo-glycan matrix
Changes to collagen bundle structure underlie softening, but mechanism unclear.
What changes happen to the cervix beginning from the first trimester?
measurable changes in compliance but retains cervical competence
What changes happen to the cervix in the weeks and days before birth?
ripening: Monocyte infiltration and IL-6 and IL-8 secretion
Hylaluron deposition
What occurs during dilation?
increased elasticity
Increased hyaluronidase expression -> HA breakdown
MMPs decrease collagen content
What happens during post partum repair?
Recovery of tissue integrity and competency
What happens to CRH levels towards the end of the pregnancy?
rise exponentially
Why does CRH bioavailability increase?
decline in CRH binding protein levels
CRH functions in labour?
promotes fetal ACTH and cortisol release
Increasing cortisol drives placental production of CRH -> Positive feedback!
stimulates DHEAS production by the fetal adrenal cortex -> substrate for estrogen production
What maintains uterine relaxation during pregnancy?
high progesterone levels
At term approaches what happens to progesterone isoforms?
switch from PR-A (activating) to PR-B/C (repressive) > functional progesterone withdrawal
At term approaches what happens to expression of estrogen receptor alpha?
increases
How does the uterus change in terms of responsiveness to oestrogen and progesterone?
‘blinded’ to progesterone action
sensitised to oestrogen action
Where is oxytocin synthesised?
utero-placental tissues
pituitary
What happens to uterine oxytocin production at the onset of labour?
increases sharply
Expression increase of oxytocin is driven by?
increase in oestrogen
What is the Ferguson reflex?
self-sustaining cycle of uterine contractions initiated by pressure at the cervix (positive feedback loop)
Oxytocin signals through what receptor?
G coupled oxytocin receptor (OXTR)
What inhibits OXTR expression pre labour?
progesterone
What stimulates expression of OXTR?
oestrogen rise
Functions of oxytocin?
Increases connectivity of myocytes in myometrium,
destabilise membrane potentials to lower threshold for contraction, enhances liberation of intracellular Ca2+ ion stores
What primary prostagladins are synthesized during labour?
PGE2
PGF2 alpha
PGI2
What drives prostagladin action in the uterus?
rising oestrogen
How does oestrogen drive prostagladin action?
activates phospholipase A2 enzyme > arachidonic acid for synthesis and stimulates OXTR > promotes PG release
Effect of PGE2 in labour
cervix re-modelling: promotes leukocyte infiltration into the cervix, IL-8 release and collagen bundle re-modelling
Effect of PGF2 alpha in labour
myometrial contractions: destabilises membrane potentials and promotes connectivity of myocytes (with oxytocin)
Effect of PGI2 in labour
myometrium: promotes myometrial smooth muscle relaxation and relaxation of lower uterine segment.
List factors other than prostagladins that have key effects in labour.
peptide hormone relaxin
nitric oxide
both implicated in cervix remodelling
Describe formation of the birth canal.
Myometrial muscle cells form a syncytium (extensive gap junctions), brachystatic (fibres do not return to full length on relaxation) contractions start from the fundus, spread down upper segment
> lower segment and cervix to be pulled up
List the steps of foetal expulsion.
head engages with pelvic space > pressure causes chin to press to chest > rotates belly to mother’s spine > head first > shoulders delivered sequentially > torso next
What happens to uterus after foetal delivery?
rapid shrinking
Uterine shrinking causes?
folding of fetal membranes, area of contact of placenta with endometrium shrinks
How to stop foetal blood flow to placenta after birth?
clamp umbilical cord
Why does uterus remain contracted after birth?
facilitate uterine vessel thrombosis
