7.1 Foetal Physiology Flashcards
What is foetal pO2?
4kPa
What factors increase foetal O2 content?
Foetal Hb variant
Increased foetal haematocrit
What factors promote oxygen exchange to the foetus at the placenta?
Increased maternal production of 2,3-DPG
Foetal Hb
Double Bohr effect
What is the increased maternal production of 2,3-DPG secondary to?
Physiological respiratory alkalosis of pregnancy
When is HbF the predominant form of Hb?
12 weeks to term
Describe the composition of HbF
2 alpha subunits, 2 gamma subunits
Why does HbF have a greater affinity for oxygen?
Because it doesnt bind 2,3-DPG as effectively as HbA
What is the double Bohr effect?
Bohr effect on maternal and foetal side
CO2 passes into intervillous blood, pH decreases, decreased affinity of Hb for O2
At the same time..
CO2 is lost, pH rises, increases affinity of Hb for O2
What is the advantage of the double Bohr effect?
Speeds up the process of oxygen transfer
How is a carbon dioxide concentration gradient maintained across the placenta?
Progesterone driven hyperventilation in mother
Lower pCO2 in maternal blood
Why are there no alterations in local pCO2 at the placenta?
As Hb gives up O2, it can accept increasing amounts of CO2
Foetus gives up CO as O2 is accepted (Haldane effect)
Why does the liver need to be bypassed in foetal circulation?
Because it is much larger in foetus than adult
Would consume all of the oxygen and nutrients
What does the ductus venosus connect?
Umbilical vein to IVC
Where does blood from the ductus venosus?
Right atrium
Why does blood flow through the foramen ovale into the LA?
Because right atrial pressure is greater than left atrial
What does the free borer of septum secundum form?
Crista dividens
How many streams of blood flow are created by the FO?
2
Where does the ductus arteriosus shunt to and from?
From RV and PT to aorta
Where does the DA join?
Joins aorta distal to the supply of the head (and heart)
Describe the foetal response to hypoxia
Redistribution of blood flow to head and heart
Heart rate slows (less oxygen demand)
What sort of stimulation leads to bradycardia in the foetus upon detection of decreased pO2 of increased pCO2 by the foetal chemoreceptors?
Vagal
What are the consequences of chronic hypoxaemia to the foetus?
Growth restriction
Behavioural changes which can impact on development
What is the most common cause of foetal chronic hypoxaemia?
Smoking
Which hormones are necessary for foetal growth?
Insulin, IGF1, IGF2, lepton, EGF, TGFa
