Foetal Circulation and Adaption

Question 1

function of placenta

Answer 1

fetal homeostasis
allows for;
gas exchange
acid-base balance
nutrient transport to fetus
waste product transport from fetus
hormone production 
transport of IgG
produces PGE2

Question 2

describe special adaptions of foetus

Answer 2

placenta included in circulation, blood not required to go t lungs/kidney/gut etc.
lungs are filled and unexpanded
liver has little role in nutrition and waste management
gut not in use

Question 3

describe foetal circulation

Answer 3

blood goes from placenta to the right side of the heart, only a tiny fraction goes to the lungs
it the travels from right side of the heart, back to the placenta

Question 4

describe the role of the placenta in the circulation

Answer 4

foetal hearts pumps blood from placenta via the umbilical arteries
blood from the placenta returns to the foetus via the umbilical vein

Question 5

describe the distribution of blood to the growing foetus from placenta

Answer 5

via 3 shunts specific to foetal life;
ductus venosus
foremen ovale
ductus arteriosus

Question 6

describe the ductus venosus

Answer 6

connects umbilical vein to the inferior vena cava;

carries majority of the placental blood straight into inferior vena cava bypassing portal circulation (liver)

Question 7

describe the foramen ovale

Answer 7

opening in atrial septum connecting the right atrium to the left atrium;
allows blood to flow from right to left atrium
allows the best oxygenated blood to enter left atrium then on to left ventricle, ascending aorta, carotids
membrane flap on the left atrium side

Question 8

describe the ductus arteriosus

Answer 8

connects pulmonary bifurcation to the descending aorta;
only 7% of right ventricle output goes to lungs, the rest goes via ductus arteriosus to join descending aorta
patency maintained by circulating prostaglandin E2 produced by placenta

Question 9

adaption of new born

Answer 9

baby inflates lungs and cries
goes from blue to pink
cord clamped and cut
sats rise from 70-90%

decrease in pulmonary vascular resistance;
breathe in - lungs physically expand
continues to drop and reaches adult levels by 2-3 months

increase in systemic vascular resistance - cord clamped and cut
more of cardiac output to lungs

foramen ovale closes
duct constriction

Question 10

describe constriction of the duct

Answer 10

Functional closure within hours to days
Anatomical closure within 7-10 days due to increase in pO2
decrease in flow and prostaglandins (E2)
also due to rise in sats, less blood flow (due to pulmonary vascular resistance) and the removal of the placenta
Ends up as fibrous ligament – ligamentum arteriosum

Question 11

describe closure of foramen ovale

Answer 11

closes as left atrium pressure exceeds the right atrium

Question 12

describe failure of the duct closure

Answer 12

very high incidence of patent ductus arteriosus in preterm infants - picked up no screening
can contribute to other preterm complications
treatment - wait and see (muscle matures and constricts duct itself), NSAIDS or surgery

Question 13

describe maintaining the duct patency

Answer 13

Some congenital heart disease causes a “duct dependent circulation”
IV prostaglandin E2 can be used to keep the duct open until an alternative shunt established or definitive surgery carried out
e.g. interruption of the aortic arch

Question 14

describe what would happen to a newborn if they had failure to adapt

Answer 14

persistent pulmonary hypertension (as pressure fails to drop)
seen in sick babies;
sepsis
hypoxic ischaemic insult
meconium aspiration syndrome
cold stress

can be related to underlying anatomical abnormality such as congenital diaphragmatic hernia

Question 15

describe persistent pulmonary hypertension of the new born

Answer 15

lung vascular resistance fails to fall
shunts remain;
right to left flow at PFO
right to left flow at PDA

results in;
blue baby
large difference between pre and post ductal oxygen saturation

Question 16

treatment of persistent pulmonary hypertension of the newborn

Answer 16

ventilation
oxygenation
high systemic blood pressure (via maintaining higher than adequate BP and inotropes)
inhaled nitric oxide
sedation
thermoregulation
correction of acidosis