Foetal physiology Flashcards
1
Q
What vessels make up the materno-foetal circulation?
A
- Foetal circulation
- Umbilical arteries
- Umbilical vein
- Foetal capillaries within chorionic villi increase SA
- Uterine arteries
- Uterine veins
- Maternal blood lakes in intervillous spaces
2
Q
Outline foetal circulation
A
- Oxygenated blood carried via umbilical vein
- Deoxygenated blood carried to placenta via umbilical arteries
- Lungs are non-functional
- Blood by-passes lungs and liver
3
Q
How is the movement of oxygen from maternal to foetal red cells is facilitated by 3 factors?
A
- Relative concentration difference between foetal and maternal blood
- A higher affinity of foetal haemoglobin for oxygen than adult haemoglobin
- Double Bohr affect
4
Q
Outline foetal PO2 concentration
A
- Foetal blood has low PO2
- 4kPa compared to adult pO2 of 11-13kPa
5
Q
Compare foetal haemoglobin to adult haemoglobin
A
- Predominant form from weeks 12-term is HbF
- 2 alpha subunits + 2 gamma subunits (instead of beta)
6
Q
Why does foetal haemoglobin have a greater affinity for oxygen?
A
- Doesn’t bind 2,3-DPG as effectively as HbA
7
Q
What is meant by a ‘double Bohr effect’?
A
- As CO2 passes into intervillous blood, pH decreases
- This decreases affinity of maternal Hb for O2
- Relative decrease in CO2 on foetal side causes foetal blood to become slightly more alkaline
- Increasing affinity of foetal Hb for O2
8
Q
What is the double Haldane effect?
A
- As maternal Hb gives up O2, it can accept increasing amounts of CO2
- Deoxygenated blood has higher affinity for CO2
- Foetus gives up CO2 as O2 is accepted
9
Q
What are the foetal circulatory shunts?
A
- Foramen ovale
- Ductus venosus
- Ductus arteriorsus
10
Q
Why is ductus venosus needed?
A
- Ductus venosus connects umbilical vein carrying oxygenated blood to IVC of foetus
- Blood enters right atrium
- By ensuring shunting of blood around liver, saturation is mostly maintained
11
Q
Why is foramen ovale needed?
A
- Creates a shunt between right atrium and left atrium
- Allows oxygenated blood to enter left ventricle and then aorta to brain
- Small amount enters right ventricle to the pulmonary trunk
- Blood bypasses lungs
12
Q
What allows the heart and brain to get the lion’s share of oxygen?
A
- Blood is pumped to aorta from left atrium
- Blood reaching left atrium has saturation of approx. 60%
13
Q
Why is ductus arteriosus needed?
A
- Shunts blood from pulmonary trunk to aorta
- Joins aorta distal to supply to head and heart
- Minimises drop in O2 saturation
- Bypasses inactive lungs
14
Q
How are foetuses adapted to overcome hypoxia?
A
- HbF
- Increased [Hb]
- Flow can redistribute to protect supply to heart and brain
- Foetal heart rate slows in response to hypoxia to reduce O2 demand
15
Q
How do foetuses detect changes in CO2 or O2?
A
- Chemoreceptors detect changes in PO2 or PCO2
- Vagal stimulation leads to bradycardia
