Foetal Development and Adaptation to Extra-Uterine Life
Lung development in late pregnancy
o Babies briefly breathe amniotic fluid
Most gas exchange is through the placenta
o Lungs are not needed in development, but they need to be prepared for extra-
uterine life
o Foetal breathing movements just use the diaphragm 1-4 hours per day
Occurs during REM sleep
o Distension during breathing stimulates growth
o There is reflex neuromuscular development
o Surfactant production reduces surface tension for lung inflation
Occurs later in lung development
Allows lungs to clear of amniotic fluid at birth
Production is stimulated by cortisol
o Antenatal treatment with glucocorticoids accelerates lung development and
surfactant production in preterm babies
Babies given glucocorticoids are more likely to have respiratory issues in
their 40’s and 50’s
To combat this, babies are often given a nebuliser after birth
containing cortisol
o Respiratory distress syndrome in premature infants is treated with surfactants
o 50% of women who go into a labour ward and don’t have any treatment done
get sent home because they aren’t actually in labour
If these women are given glucocorticoids and then their babies are
delivered at term, they may have damaged a healthy foetus
Lecithin is a surfactant that begins being produced around 24 weeks
o If the baby remains in utero until past 32 weeks, they probably won’t have too
many problems as they have a bigger lung capacity
o Liver glycogen also builds up rapidly after week 36
Means that the switch to nutrients from milk doesn’t need to be instant
because they have a few days of energy built up
o
, Modification to the foetal circulation using shunts
o Shunts incorporate the placenta into the foetal circulation
o They ensure the appropriate delivery of oxygenated blood and nutrients to the
foetus
Blood largely bypasses the foetal lung and liver
o Foetal heart
Oxygenated blood from the placenta enters the right atrium via the
inferior vena cava
Foramen ovale allows oxygenated blood in the right atrium to reach the
left atrium (2)
Heart pumps in parallel, most of the blood doesn’t go to the lungs
at this point in development
Ductus arteriosus connects aorta with pulmonary artery, further
shunting blood away from the lungs and into the aorta (3)
Mixed blood travels to the head and body, then back to the placenta via
the aorta (4)
o Umbilical cord contains the umbilical artery and umbilical vein
Blood arrives at the umbilical cord via the umbilical vein
The ductus venosus shunts oxygenated blood from the placenta away
from the semi-functional liver and towards the heart
Ductus venosus
o Oxygenated blood travels from the maternal side of placenta towards the
foetal liver via the umbilical vein
o Flow splits into two vessels
Larger is the ductus venosus- shunt that bypasses the hepatic circulation
Direct link from the umbilical cord to the vena cava
Lung development in late pregnancy
o Babies briefly breathe amniotic fluid
Most gas exchange is through the placenta
o Lungs are not needed in development, but they need to be prepared for extra-
uterine life
o Foetal breathing movements just use the diaphragm 1-4 hours per day
Occurs during REM sleep
o Distension during breathing stimulates growth
o There is reflex neuromuscular development
o Surfactant production reduces surface tension for lung inflation
Occurs later in lung development
Allows lungs to clear of amniotic fluid at birth
Production is stimulated by cortisol
o Antenatal treatment with glucocorticoids accelerates lung development and
surfactant production in preterm babies
Babies given glucocorticoids are more likely to have respiratory issues in
their 40’s and 50’s
To combat this, babies are often given a nebuliser after birth
containing cortisol
o Respiratory distress syndrome in premature infants is treated with surfactants
o 50% of women who go into a labour ward and don’t have any treatment done
get sent home because they aren’t actually in labour
If these women are given glucocorticoids and then their babies are
delivered at term, they may have damaged a healthy foetus
Lecithin is a surfactant that begins being produced around 24 weeks
o If the baby remains in utero until past 32 weeks, they probably won’t have too
many problems as they have a bigger lung capacity
o Liver glycogen also builds up rapidly after week 36
Means that the switch to nutrients from milk doesn’t need to be instant
because they have a few days of energy built up
o
, Modification to the foetal circulation using shunts
o Shunts incorporate the placenta into the foetal circulation
o They ensure the appropriate delivery of oxygenated blood and nutrients to the
foetus
Blood largely bypasses the foetal lung and liver
o Foetal heart
Oxygenated blood from the placenta enters the right atrium via the
inferior vena cava
Foramen ovale allows oxygenated blood in the right atrium to reach the
left atrium (2)
Heart pumps in parallel, most of the blood doesn’t go to the lungs
at this point in development
Ductus arteriosus connects aorta with pulmonary artery, further
shunting blood away from the lungs and into the aorta (3)
Mixed blood travels to the head and body, then back to the placenta via
the aorta (4)
o Umbilical cord contains the umbilical artery and umbilical vein
Blood arrives at the umbilical cord via the umbilical vein
The ductus venosus shunts oxygenated blood from the placenta away
from the semi-functional liver and towards the heart
Ductus venosus
o Oxygenated blood travels from the maternal side of placenta towards the
foetal liver via the umbilical vein
o Flow splits into two vessels
Larger is the ductus venosus- shunt that bypasses the hepatic circulation
Direct link from the umbilical cord to the vena cava
