9. The foetal circulation (workbook) Flashcards
which organs does the placenta replace the function of?
- foetal gut
- lungs
- kidneys
in the foetus, blood from the umbilical vein returns from the placenta to combine with what?
the venous drainage of the gut
in the absence of modification to the circulation, what would happen to the oxygenated blood of the umbilical veins?
the oxygenated blood would pass through the liver and the lungs and mix with venous blood from the body and brain before it reaches the systematic arteries - thus loosing most of its oxygen
how is umbilical venous blood shunted around the liver?
by ductus venosus
what does umbilical venous blood mixes with?
venous blood from the lower body in the ascending vena cava
why is umbilical venous blood mixing with venous blood from the lower body in the ascending vena cava not a major problem?
the lower body of a foetus is relatively small and not that metabolically active
where does venous blood from the brain travel to in a foetus?
right atrium via the descending vena cava
what prevents mixing of venous blood from umbilical vein and brain?
crista dividens
what does crista dividens do?
directs the oxygenated blood towards the foramen ovale
what is the foramen ovale?
a hole between the right and left atrium which allows blood to by-pass the right ventricle and the lungs and enter the left heart directly
where does deoxygenated blood from the brain pass to?
right atrium, RV then lungs
what do the collapsed lungs of a foetus offer?
a high resistance to blood flow, so most of the output of the right heart flows through the ductus arteriosus instead
what is the ductus arteriosus?
links the pulmonary artery with the aorta
where does the ductus arteriosus join the aorta?
at level below the arterial outflow to the brain
where is the oxygenated blood in a foetus directed to?
left heart via the foramen ovale (L-R atrium)
therefore mixed with very little blood from the lungs in the left atrium and remains well oxygenated
what happens to the oxygenated blood in the left ventricle?
pumped out to the aorta and up to the brain
what does the remaining oxygenated arterial flow join?
the flow from the ductus arteriosus (PA - aorta) to supply the rest of the body (needs are less critical than heart and brain)
where does deoxygenated blood return?
returns to the placenta in the umbilical artery for reoxygenation
what does the pattern of foetal circulation require?
the pressure in the left atrium to be LOWER than the right (right higher)
why does the the pressure in the left atrium need to be LOWER than the right?
- so blood flows the right way through foramen ovale (R to L)
- the pressure in the pulmonary artery is higher than aorta
- flow in ductus arteriosus will be the right way (PA to aorta)
with changes in the foetal circulation, what is the partial pressure of oxygen in foetal blood like?
the ppO2 of foetal blood is v LOW compared to adult
how is the low ppO2 of foetal blood achieved?
- a different haemoglobin
2. higher haemoglobin levels (within RBC)
how is foetal haemoglobin different from adults?
2 gamma and 2 alpha instead of 2 alpha and 2xß chains
foetal haemoglobin has a much HIGHER affinity for oxygen - carry more O2 at lower pO2
how does the foetus have a higher haemoglobin level?
the neonate has a haemoglobin level of at least 18g.dl-1
foetus has more haemoglobin compared to adults
what is the foetal pCO2 like? why?
foetus has relatively normal pCO2
the maternal CO2 levels are LOWERED by hyPERventilation stimulated by progesterone
(hyperventilation of mother allows for normal pCO2 within foetus)
does the foetus make breathing movements? why?
YES
to draw amniotic fluid in and out of lungs
what is produced in foetal lungs from around week 20?
surfactant produced by type II pneumocytes (lung epithelium)
when is production of surfactant in foetus significantly increased?
after week 30 when the alveoli open in significant number and the surface area dramatically increases
what is the function surfactant?
lowers alveolar surface tension so that inspiration is made with LESS effort post-natally
what does a deficiency in surfactant result in?
pre-term infants (pre-mature)
can lead to respiratory distress of the newborn
