Revision - Foetal Circulation Flashcards
What does the ductus venosus connect?
Umbilical vein & inferior vena cava
Allows blood to bypass the liver
What is required to keep the ductus arteriosus open?
Prostaglandins
After birth, what happens to the ductus venosus?
Immediately after birth the ductus venosus stops functioning because the umbilical cord is clamped and there is no flow in the umbilical veins.
Becomes ligamentum venosum.
What is the cardiac output in adults?
Approx 5L/min
Describe foetal circulation at the liver
1) Oxygenated blood from the placenta travels via the umbilical vein, which branches into the L and R umbilical veins at the liver.
2) The R umbilical vein provides oxygenated blood to the liver via the portal vein, whilst the L umbilical vein branches into the ductus venosus, which bypasses the liver to carry oxygenated blood directly into the IVC
3) A mix of oxygenated (from ductus venosus) and deoxygenated (from liver and the rest of the body) blood then enters the right atrium via the IVC, also mixing with the SVC.
Which vessel provides oxygenated blood to the liver in foetal circulation?
R umbilical vein
Which vessel branches into the ductus venosus in fetal circulation?
L umbilical vein
What do the umbilical arteries arise from?
1) The aorta bifurcates into the right and left common iliac arteries.
2) These split further into the internal and external iliac arteries.
3) Each of the internal iliac arteries give rise to an umbilical artery, which travel alongside the umbilical vein to bring deoxygenated blood back to the placenta.
what do the umbilical vessels become after birth?
umbilical vein –> round ligament of liver
umbilical artery –> superior vesical arteries
Does a murmur becoming louder on standing indicate an innocent murmur or not?
No - requires more investigations.
What are the 3 differentials of a pansystolic murmur?
1) Tricuspid regurgitation
2) Mitral regurgitation
3) VSD
Where would a pansystolic murmur caused by mitral regurgitation be heard loudest?
At the mitral area (fifth intercostal space, mid-clavicular line).
Where would a pansystolic murmur caused by tricuspid regurgitation be heard loudest?
At the tricuspid area (fifth intercostal space, left sternal border).
Where would a pansystolic murmur caused by a ventricular septal defect be heard loudest?
Left lower sternal border
What are the 3 differentials for an ejection systolic murmur?
1) Aortic stenosis
2) Pulmonary stenosis
3) HOCM
Where would an ejection systolic murmur caused by hypertrophic obstructive cardiomyopathy be heard loudest?
4th intercostal space at left sternal border
What is splitting of the 2nd heart sound?
When pulmonary valve closes after aortic valve
When can splitting of the 2nd heart sound be normal?
if it varies with inspiration & expiration
What does a ‘fixed split’ second heart sound mean?
The split does NOT change with inspiration and expiration.
What heart condition can cause a fixed splitting of 2nd heart sound?
ASD
Blood is flowing from the LA into the RA across the ASD, increasing the volume of blood that the RV has to empty before the pulmonary valve can close. This doesn’t vary with respiration.
What murmur can be heard in ASD?
A mid-systolic, crescendo-decrescendo murmur, with a fixed split second heart sound.
Heard at upper left sternal border.
What type of murmur can a patent ductus arteriosus cause?
A small patent ductus arteriosus may not cause any abnormal heart sounds.
More significant PDAs cause a normal first heart sound with a continuous crescendo-decrescendo “machinery” murmur that may continue during the second heart sound, making the second heart sound difficult to hear.
Why may the murmur in a PDA be difficult to hear?
As the murmur may continue during the second heart sound, making the second heart sound difficult to hear.
What does the murmur in Tetralogy of Fallot arises from?
Pulmonary stenosis
Ejection systolic murmur heard loudest at the pulmonary area (second intercostal space, left sternal border).