Fetal Physiology Flashcards
Describe the fetal circulation
Oxygenated blood carried via the umbilical vein
Deoxygenated blood carried via the umbilical arteries
Describe gas exchange at the placenta
Diffusion barrier = small, decreases as preg proceeds
Gradient of partial pressures required = maternal pO2 increases, fetal pO2 must be lower than maternal pO2
Increased maternal prod of 2,3 DPG = decreased affinity
Fetal Hb
Double Bohr effect
What is fetal Hb?
2 alpha, 2 gamma subunits
Predominant at 12 weeks
Greater affinity for O2 because it doesn’t bind 2,3-DPG as effectively as HbA (adult Hb)
Outline the double Bohr effect
As CO2 passes to intervillous blood = blood pH decreases = Bohr effect
Decreasing affinity Hb for O2
At the same time as CO2 is lost = pH rises = Bohr effect
Increasing affinity of Hb for O2 = speeds up process of O2 transfer
Why is pCO2 lower in the maternal blood?
Progesterone driven hyperventilation
Outline the double Haldane effect
As Hb gives up O2 = can accept increasing amounts of CO2
Fetus gives up CO2 as O2 is accepted
No alterations in local pCO2
Why does fetal blood need to bypass the liver?
Keeping blood away from liver = maintain high levels of saturation
A small amount of blood does need to enter the R ventricle, why?
For proper devel of the R ventricle it needs small amount of blood to push against
Free border of septum secundum forms crista dividens = 2 streams of blood flow = minor proportion to RA
Name fetal shunts and where they are found
Ductus venosus = bypass liver, connect umbilical vein to IVC
Foramen ovale = from R atria to L atria
Ductus arteriosis = pulmonary trunk to aorta
How does the fetus respond to hypoxia?
HbF increases
Redistribution of flow to protect supply to heart and brain
Vagal stim = HR slows to reduce O2 demand (in adults vagal inhibition = tachycardia)
What results from chronic hypoxaemia?
Growth restrictions
Behavioural changes
= impact on devel
Most common reason = smoking
What hormones are critical for fetal growth?
IGFs
How does malnutrition effect fetal growth?
Symmetrical growth restriction = entire fetus smaller than expected
Asymmetrical growth restriction = big head, restricted abdo
What is amniotic fluid?
Fetal urine – production by 9 weeks
Encloses embryo/fetus
Protection
Amount proportional to fetal size
How does amniotic fluid aid the devel of the lungs?
Inhaling amniotic fluid while practising breathing movements
Contains factors essential for lung devel
