Foetal Physiology Flashcards
What type of blood is carried in the umbilical vein?
Oxygenated blood
What type of blood is carried in the umbilical arteries?
Deoxygenated blood
How does gas exchange take place at the placenta?
Thin diffusion distance
Down gradient of partial pressures
So foetal pO2 needs to be lower than maternal pO2
What is the normal pO2 of foetal blood?
4kPa
What factors promote O2 exchange at the placenta?
Increased maternal production of 2,3 DPG
Foetal haemoglobin
Double Bohr effect
What makes up foetal haemoglobin?
2 α subunits + 2 γ subunits
Why does foetal haemoglobin have greater affinity for oxygen?
Doesn’t binf to 2,3-DPG as effectively as adult Hb
What is the double bohr effect?
Bohr effect on both mother’s haemoglobin and foetal haemoglobin
What happens to the mother with the double bohr effect?
CO2 passes into intervillous blood
pH decreases
Bohr effect
Decreases affinity of Hb for O2
What happens to the foetus with the double Bohr effect?
CO2 is lost
pH rises
Bohr effect
Increases affinity of Hb for O2
How is CO2 transferred?
Double Haldane effect
Progesterone driven hyperventilation = lower maternal pCO2
- down concentration gradient
What is the double Haldane effect?
As Hb gives up O2, it can accept more CO2
Foetus gives up CO2 as O2 is accepted
No changes in local CO2
What are the foetal circulation shunts?
Ductus venosus
Ductus arteriosus
Foramen ovale
What is ductus venosus?
Connects umbilical vein to IVC
- blood enters directly into RA
- shunts blood around liver
- maintains saturation
What is ductus arteriosus?
Shunt from RV to aorta
- joins aorta distal to supply of head
- minimises drop in O2 sats
What is foramen ovale?
Hole between RA + LA
- pressure in RA > pressure in LA
- blood flows into left atrium
- heart + brain get good supply of oxygen
Which shunts bypass the lungs?
Foramen ovale
Ductus arteriosus
What is the foetal response to hypoxia?
Redistribution of flow to supply heart and brain
Heart rate decreases to reduce O2 demand
What are the effects of chronic hypoxaemia?
Growth restriction
Behavioural changes
What hormones are necessary for foetal growth?
Insulin
IGF
Leptin
What is symmetrical growth restriction?
Small head + small body
What is asymmetrical growth restriction?
Normal head + small body
What is the dominant cellular growth mechanism in weeks 0-20?
Hyperplasia
What is the dominant cellular growth mechanism in weeks 20-28?
Hyperplasia + hypertrophy
What is the dominant cellular growth mechanism in weeks 28- term?
Hypertrophy
What is amniotic fluid?
FLuid that makes up amniotic sac
What is the role of amniotic fluid?
Protection
Contributes to lung development
What is volume of amniotic fluid at 8 weeks?
10ml
What is the volume of amniotic fluid at 38 weeks?
1L
What is the composition of amniotic fluid?
98% water Electrolytes Creatinine Urea Renin Foetal cells
What happens to amniotic fluid during pregnancy?
Foetus swallows fluid to absorb water + electrolytes
Most is excreted as urine
What makes up meconium?
Debris from amniotic fluid + intestinal secretions
What is amniocentesis?
Sampling of amniotic fluid
What is oligohydramnios?
Lack of amniotic fluid production
What can cause oligohydramnios?
Foetal kidney malfunction
Premature membrane rupture
Placental insufficiency
What is polyhydramnios?
Increased amniotic fluid production
What can cause polyhydramnios?
Excessive urine production
Gestational diabetes
Maternal hypertension
How is bilirubin metabolised in the foetus?
Clearance of bilirubin handled by placenta
Foetus cannot conjugate bilirubin
