18) Fetal Physiology Flashcards
What factors optimise diffusion across the placenta?
Small diffusion barrier- decreases as pregnancy proceeds
Concentration gradient between pO2 in mother and fetus
What maternal and fetal factors increase gas exchange?
Increased maternal 2,3-BPG
Fetal haemoglobin
Double Bohr effect
Describe the features of fetal haemoglobin:
HbF from 2 alpha and 2 gamma subunits
Increased affinity for O2 as doesn’t bind 2,3-BPG as well as HbA
What is the double Bohr effect?
As CO2 passes into maternal blood, pH decreases and oxygen is given up
At same time, CO2 given up by fetus, which increases pH and increases fetal affinity for O2
What promotes CO2 transfer from fetus to mother?
Progesterone driven hyperventilation in mother which lowers pCO2 of maternal blood providing a conc. grad.
What are the shunts in fetal circulation?
Ductus venosus (bypass liver) Foramen ovale (RA -> LA) Ductus arteriosus (bypass lungs)
What is the function of the ductus venosus?
Connects umbilical vein to IVC
Bypasses liver to maintain saturation
What is the function of the crista dividens?
Directs oxygenated blood to LA via foramen ovale
What is the function of foramen ovale?
Shunt from RA to LA so greater supply to LV to supply blood to brain and body
What is the function of ductus arteriosus?
Between pulmonary artery and aorta to bypass lungs and minimise drop in O2 saturation
Describe the fetal response to hypoxia?
Redistribution of flow to protect supply to heart and brain
Decrease HR to reduce O2 demand
Increased Hb
If hypoxia is chronic, what could be the result for the fetus?
Growth restriction Behavioural changes (less movement)
What hormones are needed for fetal growth?
Insulin, IGF II (T1), IGF I (T2-3), leptin
What is asymmetrical growth restriction?
Abdominal growth lags, head spared
What is symmetrical growth restriction?
Generalised and proportional restriction
