Foetal and Neonatal Cardiorespiratory Physiology Flashcards
By which stage in gestation is the placenta fully formed?
The placenta is formed by week 14 of gestation.
How do oxygen, carbon dioxide and nutrients move between the maternal intervillous space and chorionic villi?
Oxygen, carbon dioxide and nutrients move between the maternal intervillous space and chorionic villi by diffusion.
How does the composition of the umbilical arteries compare to the composition of the umbilical veins in the placenta?
The umbilical arteries are deoxygenated and lack nutrients, whereas the umbilical veins are oxygenated and contain nutrients.
*The naming is counterintuitive because they’re named according to the direction of blood flow to the placenta rather than to the foetus. It’s like the pulmonary vessels in adults.
List the values for PO2 in the uterine artery and vein.
List the values for PO2 in the umbilical artery and vein.
How saturated is the foetal haemoglobin with oxygen at this PO2?
- PO2 in the uterine artery is 12.7kPa.
- PO2 in the uterine vein is 5.6kPa
- PO2 in the umbilical artery is 3.2kPa.
- PO2 in the umbilical vein is 4.2kPa.
- At 4.2kPa, foetal haemoglobin is 75% saturated with O2.
List the values for PCO2 in the uterine artery and vein.
List the values for PCO2 in the umbilical artery and vein.
- PCO2 in the uterine artery is 5.3kPa.
- PCO2 in the uterine vein is 6.1kPa.
- PCO2 in the umbilical artery is 6.6kPa.
- PCO2 in the umbilical vein is 5.8kPa.
Does the foetal blood achieve equilibrium with the maternal blood in the placenta for oxygen and carbon dioxide?
Why is this?
- The foetal blood does achieve equilibrium (almost) with maternal blood for CO2.
- The foetal blood does not achieve equilibrium with maternal blood for O2 i.e. oxygen exchange is relatively limited in the placenta.
This is because:
1 - The placental barrier is more permeable to CO2 than O2.
2 - Not all of the maternal blood comes in contact with the chorionic villi (makes the gap bigger because of point 1).
3 - The placental tissue is highly active and consumes 20% of O2 in the maternal artery.
How does the structure of foetal haemoglobin (HbF) compare with the structure of adult haemoglobin?
- Foetal haemoglobin comprises 2 alpha and 2 gamma subunits.
- Adult haemoglobin comprises 2 alpha and 2 beta subunits.
How does the level of foetal haemoglobin change with advancing gestation?
- Foetal haemoglobin reaches peak level at 10 weeks.
- This level is maintained until 30 weeks.
- By term, the level of foetal haemoglobin declines to 80% of the peak level.
- The remaining 20% gradually disappears after birth.
How does foetal haemoglobin differ functionally from adult haemoglobin?
What gives rise to this difference?
How is this advantageous?
- Foetal haemoglobin has a higher affinity for oxygen than adult haemoglobin (the oxygen saturation curve in foetal Hb is shifted to the left relative to adult Hb).
- This is because foetal haemoglobin doesn’t interact with 2,3-DPG.
- This is advantageous as there are limiting factors in the placenta for O2 exchange (as seen in a previous card).
- Remember 2,3-DPG is the metabolite formed within the RBC from the glycolytic pathway which decreases affinity for oxygen. This is useful for oxygen unloading.
In the placenta, how does the foetal blood affect the oxygen affinity of the maternal blood?
How is this advantageous?
- As the maternal blood picks up CO2 from the foetus, the O2 saturation curve of the maternal blood experiences a Bohr shift to the right.
- There is a concomitant Bohr shift to the left in the foetal blood as it loses CO2.
- This is advantageous as this further increases affinity of foetal haemoglobin for oxygen, which is necessary as the placenta is a limiting environment for O2 exchange (as seen in a previous card).
- Remember the Bohr effect is the reduction in affinity for oxygen with increasing concentration of CO2.
How does the concentration of foetal haemoglobin in foetal blood compare with the concentration of adult haemoglobin in adult blood?
- Foetal blood has 18g of HbF per dl.
- Adult blood has 15g of Hb per dl.
List the 3 shunts in the foetal circulation.
What is the function of these shunts?
1 - Ductus venosus.
2 - Foramen ovale.
3 - Ductus arteriosus.
- These shunts optimise oxygen delivery (particularly to the brain).
What is the ductus venosus?
The ductus venosus is a shunt from the umbilical vein through the liver to join the inferior vena cava.
What is the foramen ovale?
The foramen ovale is a shunt between the right and left atria.
What is the ductus arteriosus?
The ductus arteriosus is a shunt between the pulmonary artery and the aorta.