Interventricular septum development

Question 1

1st step

Answer 1

Muscular ventricular septum forms;

opening called interventricular foramen

Question 2

2nd step

Answer 2

AP septum rotates and fuses with muscular ventricular septum to form membraneous interventricular septum;
this closes IV foramen

Question 3

3rd step

Answer 3

Growth of endocardial cushion separates atria from ventricles and contributes to both atrial separation and membraneous portion of the IV septum.

Question 4

Pathology:

membranous septal defect

Answer 4

Initial left-to-right shunt,

which later reverses to right-to-left shunt due to the onset of pulm HTN (Eisenmenger’s syndrome).