CVS 7 - Cardiac Embryology (Part 2)

Question 1

What 4 septum’s must be created during development?

Answer 1

1) An outflow septum
2) A.V septum (embedded within this will be the AV valves)
3) Inter-atrial septum separates the primitive atrium into a left and right (so we can separate oxygenated and deoxygenated blood)
4) Inter-ventricular septum to separate the primitive ventricle into a L+R ventricle.

Question 2

What needs to fuse with the interventricular and interatrial septums in order to have full septation of the heart?

Answer 2

• The endocardial cushions, which meet and help separate the atria and ventricles.

Question 3

How is shunting of blood from the right to left atrium ensured so that the lungs can be bypassed?

Answer 3

Blood flows from the right atrium through the foramen ovale (underneath the septum secundum), and through the septum primum via the ostium secundum.

NB: The ostium primum gets smaller as the septum primum grows. The septum primum eventually fuses with the ECC’s - and the septum secundum appears via apoptosis in the septum primum.

Question 4

In which ways can atrial septal defects occur?

Answer 4

• Usually by absence or underdeveloped inter-atrial septum
• Can also get patent foramen ovale, which is where the septum primum and secundum fail to fuse together after birth - therefore communication between the L+R atrium continues.

Question 5

What is hypoplastic left heart syndrome?

What is thought to be the primary cause?

Answer 5

• Where children are born with a single ventricle
• The ostium secundum is too small - so the left side of the heart does not receive enough blood. This leads to a very small L atrium and ventricle, so the right side of the heart has to supply the whole body.

Question 6

What are the 2 components of the interventricular septum?

Answer 6

1) The membranous component - arising from the ECC’s
2) The muscular component

• Both combine to form the entire interventricular septum.

Question 7

What are congenital heart defects typified by?
What are the causes?
Name 3 congenital heart defects.

Answer 7

• Abnormal/absent structures, e.g.: the septa, chambers of vessels
• Genetic factors, environmental factors or can be idiopathic
  1) Patent ductus arteriosus (PDA) 2) Transposition of the great arteries 3) Tetralogy of fallot

Question 8

What are the key features of PDA, transposition of the great arteries and tetralogy of fallot?

Answer 8

1) PDA is when the ductus arteriosus fails to close - this allows oxygenated blood from LV to flow back to the lungs by passing from the aorta to the pulmonary artery.
2) Transposition of the great arteries - The pulmonary artery now comes from LV and aorta now comes from RV. Pulmonary and systemic circulation now run independent of each other - child can die rapidly upon birth.
3) Tetralogy of Fallot - a condition where 4 abnormalities cause deoxygenated blood to flow out of the heart into the systemic circulation. 1) Overriding aorta (sits over RV) 2) Pulmonary trunk too small - leading to pulmonary stenosis 3) RV hypertrophy as RV has to work harder due to stenosis 4) Ventricular septal defects.