Adaptation 2 Flashcards
1
Q
What is the difference in the foetal circulation?
A
- The placenta is where the oxygen and waste transport occurs, so doesn’t need to go via the lungs
- Has 3 shunts: ductus arteriosus (between pulmoary artery and aorta), Foramen ovale (between atria), and ductus venosus (left umbilical vein to IVC)
- These allow the blood to bypass the lungs
2
Q
Adult vs Foetal Hb
A
- Adult = 2 alpha and 2 beta chains
- Foetal = 2 alpha and 2 gamma chains
- The gamma chain is the main b-globin equivalent until about 6 months
- HbF binds oxygen with greater affinity than HbA, allowing oxygen to be transferred from mother to baby across the placenta. As O2 molecules bind to HbF, it becomes easier for more to bind
- HbF is saturated quicker than HbA
3
Q
What is 2,3-DPG?
A
- 2,3-Diphosphoglycerate
- binds to deoxyHb with greater affinity than oxyHb
- promotes the release of oxygen - pushes the curve to the right
- Binding to the deoxyHb stabilises the T-state conformation, making it harder for oxygen to bind Hb and more likely to be released to adjacent tissues
- Part of a feedback loop that can help prevent tissue hypoxia
4
Q
Why is there high 2,3-DPG levels in pregnant women?
A
- 30% increase in IC 2,3-DPG
- lowers the maternal Hb affinity for oxygen, therefore allowing more oxygen to be offloaded to the foetus in the maternal uterine arteries
5
Q
Why does the foetus have low sensitivity to 2,3-DPG?
A
- So its haemoglobin has a higher affinity for oxygen
- Therefore although the pO2 in the uterine arteries is low, the foetal umbilical arteries (which are deoxygenated), can still get oxygenated blood from them
6
Q
Briefly describe the foetal circulation
A
- Blood comes up from IVC and directed to foramen ovale (between atria)
- The most oxygenated blood goes to the head and brain
- Instead of blood going to the lungs, it goes through the ductus arteriosus (straight from pulmonary artery to aorta)
- Vascular resistance in foetal lungs is very high, blood goes the path of least resistance -> the systemic circulation where BVs are wider
7
Q
What is the path of the umbilical arteries?
A
- Umbilical arteries course downwards to the internal iliac arteries before entering the aorta
- They supply the buttocks and the lower extremities via the latter part of the internal iliac arteries
- The umbilical vein courses upwards along the falciform ligament to the underside of the liver
- Here it divides into two vessels, the portal vein and the ductus venosus.
- The ductus venosus joins with the IVC
8
Q
What happens to the foetal circulation at birth?
A
- Cord is stretched and cut - placental circulation ceases
- Umbilical vessels constrict - stretch and rise in oxygen tension
- Shunts close: Flow through ductus venosus falls, fall in venous return through IVC, closes after 3-10 days
9
Q
What happens when pulmonary vascular resistance falls during birth?
A
- Lung expansion
- Pulmonary stretch receptors kic in
- Increased oxygen tension
- 8-10x rise in blood flow
- Baby takes big breath, lungs expand, pulls vessels open
- Increased oxygen causes vasodilation of pulmonary BVs - more blood from lungs to left atrium.
- Causes flap valve between left and right atrium to close
10
Q
What can cause patent ductus arteriosus?
A
- Premature babies
- Babies with respiratory distress
- Down’s
- Rubella
- Congenital heart disease
11
Q
What are the symptoms of patent DA?
A
- Can be asymptomatic
- Can lead to heart failure - extra blood from left side of circulation. Blood from aorta into pulmonary circulation, goes across pulmonary artery into lungs
- Left side is pumping blood to both systemic circulation and the lungs
12
Q
What is the treatment for PDA?
A
- Indomethacin
- Ibuprofen
- Surgery
13
Q
What is an atrial septal defect?
A
- Most common congenital cardiac malformation in adults
- Causes left to right shunt due to high compliance of the RA, and the difference in pressure between the two atria
- Because of this, the pulmonary circulation has increased BP
- A person with no other heart defect, or a small defect, may not have symptoms (yet)
14
Q
What would be symptoms of an atrial septal defect?
A
- Difficulty breathing (dyspnoea)
- Frequent respiratory infections in children
- Heart palpitations in adults
- Shortness of breath with activity
15
Q
What sort of factors determine if the person will have to have surgery for an ASD?
A
- Size of the defect
- The amount of extra blood flowing through the opening
- If they have symptoms
- In infants, small ASDs (less than 5mm) will often cause no problems, or will close without treatment
- Larger ASDs (8-10mm) often dont close and may need a procedure
