9.1 Fetal Physiology Flashcards
(42 cards)
What type of blood is carries in the umbilical vein?
Oxygenated blood
What type of blood is carried in the umbilical arteries?
Deoxygenated
What adaptations are present to increase fetal partial pressure of O2?
Fetal haemoglobin variant
Fetal haematocrit is increased over that in the adult
Increased maternal production of 2,3 DPG
Double Bohr effect
What stimulated the increased maternal production of 2,3 DPG
Secondary to physiological respiratory alkalosis of pregnancy
When is HbF the predominant form of haemoglobin in the foetus?
At week 12
When does the foetus begin producing HbA?
Slowly produced from week 12
What is the subunits of HbF?
2 alpha subunits and 2 gamma units
Why does HbF have a higher affinity for oxygen than HbA?
As HbF doesn’t bing 2,3-DPG as effectively as HbA.
Therefore binds O2 at a higher affinity as doesn’t dissociate O2 as easily as HbA
What is the function of the double Bohr affect?
To speed up the process of O2 transfer at the placenta
What is the double Bohr affect?
- Decreased maternal Hb affinity for O2 - CO2 passes into intervillous blood vessels in the placenta. Causes decrease in pH. Bohr affect, O2 released
- Increased fetal Hb affinity for O2 - CO2 lost from umbilical arteries, causing pH to rise. Bohr affect. Increased affinity of fetal Hb for O2
How is the concentration gradient of CO2 between maternal and fetal blood maintained?
Progesterone driven hyperventilation causes mother to blow off CO2. Lowers pCO2 in maternal blood to maintain a concentration gradient where there is less pCO2 in the maternal blood
What is the double haldane effect seen in pregnancy?
- As maternal Hb releases O2 at the placenta, it can accept increasing amounts of CO2
- As foetus Hb releases CO2 at the placenta, it can accept O2.
This helps maintain the CO2 concentration gradient between maternal and foetal blood.
Why must foetal blood be oxygenated at the placenta?
As fetal lungs are non-functional
Where in the heart does oxygenated blood from the umbilical vein drain into?
RV
What are the fetal circulatory shunts?
Ductus venosus
Foramen ovale
Ductus arteriosus
Why does blood by pass liver?
As liver would consume much of the nutrients and oxygen that have just been gained from diffusion at the placenta. Important that this nutrients is available for other developing structures
What is the function of the ductus venosus?
Connects the umbilical vein to the IVC and then into the right atrium
Shunts the blood around the liver to maintain/preserve the pO2 and nutrient saturation for developing structures such as the brain.
What is the function of the foramen ovale?
Allows blood flow between right and left atrium
Right atrial pressure is greater than that in the left atrium
Forces leaves of FO apart and blood flows into LA and then into the aorta
What is the crista dividens?
A crest on the free border of the septum secundum
What is the function of the crista dividens?
Creates 2 streams of blood flow
Majority flows into the LA to be pumped around body
Majority goes into RV to ensure muscular development of the RV. Mixes with blood from the SVC (deoxygenated)
Describe the blood supply entering the left atrium in the foetus
- Small amount of pulmonary venous return - deoxygenated blood from development of the lungs
- Oxygenated blood through the foramen ovale.
What is the oxygen saturation of blood in the LA of foetus?
60%
Which structures get the largest amount of nutrients in the foetus?
Heart and lungs
What is the function of the ductus arteriosus?
By-passes developing pulmonary circulation
Shunts blood from RV and PT to aorta
Joins aorta distal to the supply
to the head (and heart), minimising drop in O2 saturation
