Adaptation At Birth II
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How does gas, nutrient and waste exchange occur within the baby, in terms of the circulation? (Use names of arteries)
• Umbilical arteries come to mother with deoxygenated blood • Pick up oxygen from uterine artery (high O2/nutrients) • Blood arrives to foetus via umbilical vein • Then progresses to the foetal heart
What is the purpose of placental villi?
Increase SA for diffusion
What are the 2 forms as to how Oxygen is carried in the blood?
• Dissolved in plasma + RBC water (2%) • Reversibly bound to haemoglobin (98%)
What is the structure of adult haemoglobin?
• 2 alpha chains • 2 beta chains
Foetal haemoglobin has high alpha-globin and some beta-globin, there are also similar chains to these. What is the main beta-globin equivalent in the foetus?
• Gamma - continues to be main one until 6 months old • Other beta-equivalent chain is epsilon • Other alpha-equivalent chain is zeta
So, what is the structure of foetal haemoglobin?
• 2 alpha chains • 2 gamma chains
How is foetal haemoglobin functionally different to adult haemoglobin and why is this?
• HbF binds oxygen with greater affinity than HbA • So at a lower level of oxygen the HbF is better saturated than HbA • Allows oxygen to be transferred from mother to baby across placenta (like a leach) • This is caused by a single amino acid change
What is 2,3-Diphosphoglycerate?
• Side product of glycolysis • 2,3-DPG binds to deoxygenated Hb with greater affinity than oxygenated Hb • Promotes release of Oxygen • Pushes Hb curve to the right (as does acidity + high temp)
How does 2,3-DPG help the foetus?
• 2,3-DPG does not bind to HbF as effectively as it binds to HbA • So HbF binds Oxygen with greater affinity than to HbA
50-60% of the blood from the umbilical vein (oxygenated) goes to the IVC. Where does the rest go?
Remaining 40-50% goes straight to the liver as it is very metabolically active
What is the pathway of the oxygenated blood (50-60%) that reaches the IVC in the foetus?
• from umbilical vein -> via ductus venosus • to the inferior vena cava • to the right atrium • blood from legs also joins IVC to right atrium • junction between IVC + R atrium = Eustachian valve • this oxygenated blood goes from R atrium to L atrium • via foramen ovale • then down to left ventricle -> up to aorta • then to coronary arteries -> then arteries supplying head + neck
What does the Eustachian valve do?
Helps to direct the flow of oxygen-rich blood through the right atrium into the left atrium and away from the right ventricle.
Where does the deoxygenated blood from the SVC go?
• Down into right ventricle • Then up to pulmonary artery • But instead of going to lungs, goes into next shunt - ductus arteriosus • To join aorta • This is bc lungs aren’t doing their job atm • Pulmonary circulation resistance is very high so this helps to guide blood into systemic circulation/aorta via the less resistant ductus arteriosus
What do the umbilical arteries supply?
Supply the buttocks + lower extremeties via the lateral part of the internal iliac arteries.
What happens upon birth?
• Placental circulation ceases • Umbilical vessels constrict - stretch + rise in oxygen tension • Shunts close • Flow through ductus venosus falls • Fall in venous return through IVC • Closes over 3-10 days • Baby takes big breath, lungs expand • Expansion pulls blood vessels open + pulm vessels dilate
How does pulmonary vascular resistance fall?
• Lung expansion • Pulmonary stretch receptors • Increased oxygen tension • Pulmonary vessels dilate • 8-10x rise in blood flow
How and when does the foramen ovale close?
• Fall in pulmonary vasc resistance -> rise in venous return to left atrium • RA and LA pressures equalise • Flap of foramen ovale pushed against atrial septum • Closes within mins-hours of birth
How and when does the ductus arteriosus close?
• Fall in pulmonary vasc resistance leads to bidirectional flow in ductus arteriosus • Closes due to oxygen rise • in 96 hours
Transition from the pre-natal circulation state may not be permanent as pulmonary arterioles are very reactive and can begin to constrict again to certain stimuli. What are these stimuli and what do they lead to?
• Stimuli: • Hypoxia • Hypercarbia • Acidosis • Cold Rise in PVR and right-left shunting: at risk of foetal circulation
What is the trigger for the ductus arteriosus to close?
High oxygen level
Patent ductus arteriosus (PDA) is a condition wherein the ductus arteriosus fails to close after birth. Who is PDA common in?
• Premature babies • Babies w/ respiratory distress • Down syndrome • Rubella • Congenital heart disease
What does the murmur for patent ductus arteriosus sound like?
continuous “machine-like”
What will babies present with if they’re developing heart failure as a result of patent ductus arteriosus?
• Fast breathing • Increased work of breathing • Sweating during feeding • Poor feeding • Poor growth • Rapid pulse • Bounding pulse
What is the treatment for patent ductus arteriosus?
• Drugs - indomethacin, ibuprofen • Surgery