First Aid USMLE STEP 1: Cardiovascular| 2025/2026 Update | 100%
Correct -Grade A+ Assured.
.
Truncus arteriosus gives rise to __________. - (Correct Answer) - Ascending aorta and
pulmonary trunk
Bulbus cordis gives rise to __________. - (Correct Answer) - Smooth parts (outflow tract) of left
and right ventricles
Endocardial cushion gives rise to? - (Correct Answer) - Atrial septum ,membraneous
interventricular septum; AV & semilunar valves
Primitive atrium gives rise to __________. - (Correct Answer) - Trabeculated (muscular)
portions of the left and right atria
Primitive ventricle gives rise to __________. - (Correct Answer) - Trabeculated (muscular)
portions of the left and right ventricles
Primitive pulmonary vein gives rise to __________. - (Correct Answer) - Smooth part of the
right atrium
Left horn of sinus venosus gives rise to __________. - (Correct Answer) - Coronary sinus
Right horn of sinus venosus gives rise to __________. - (Correct Answer) - Smooth part of the
right atrium (sinus venarum)
,[Type here]
Right common cardinal vein and right anterior cardinal vein gives rise to __________. - (Correct
Answer) - Superior vena cava (SVC)
When does the heart beat begin to beat spontaneously? - (Correct Answer) - -4 weeks of
development
-First functional organ in vertebrate embryos
What is cardiac looping? - (Correct Answer) - -Primary heart tube loops to establish left-right
polarity; begins in week 4 of gestation.
Defect in left-right dynein (involved in L/R asymmetry) can lead to___________, as seen in
Kartagener syndrome (primary ciliary dyskinesia). - (Correct Answer) - Dextrocardia
What is a foramen/ostium? - (Correct Answer) - opening
What is a septum? - (Correct Answer) - wall
Septation of atria (7 Steps) - (Correct Answer) - 1. Septum primum grows toward endocardial
cushions, narrowing foramen primum.
2. Foramen secundum forms in septum primum (foramen primum disappears).
3. Septum secundum develops as foramen secundum maintains right-to-left shunt.
4. Septum secundum expands and covers most of the foramen secundum. The residual foramen
is the foramen ovale.
5. Remaining portion of septum primum forms valve of foramen ovale.
,[Type here]
6. (Not shown) Septum secundum and septum primum fuse to form the atrial septum.
7. (Not shown) Foramen ovale usually closes
soon after birth because of increased LA pressure.
Patent foramen ovale is caused by a failure of __________ and ___________ to fuse after birth.
What can this lead to? - (Correct Answer) - -Caused by failure of septum primum and septum
secundum to fuse after birth; most are left untreated.
-Can lead to paradoxical emboli (venous thromboemboli that enter systemic arterial circulation),
similar to those resulting from an ASD.
Septation of the ventricles (3 steps) - (Correct Answer) - 1. Muscular ventricular septum forms.
Opening is called interventricular foramen.
2. Aorticopulmonary septum rotates and fuses with muscular ventricular septum to form
membranous interventricular septum, closing interventricular foramen.
3. Growth of endocardial cushions separates atria from ventricles and contributes to both atrial
septation and membranous portion of the interventricular septum.
What is the most common congenital cardinal anomaly? - (Correct Answer) - VSD
Most common location of VSD? - (Correct Answer) - The membranous septum
Outflow tract formation - (Correct Answer) - Truncus arteriosus rotates; neural crest and
endocardial cell migrations cause truncal and bulbar ridges that spiral and fuse to form
aorticopulmonary septum to form ascending aorta and pulmonary trunk.
, [Type here]
What are the conotruncal abnormalities associated w/ failure of neural crest cells to migrate? -
(Correct Answer) - Transposition of the greta vessels
Tetralogy of Fallot
Persistent truncus arteriosus
Aortic/pulmonary valves are derived from ____________. - (Correct Answer) - The endocardial
cushions of outflow tract.
Mitral/tricuspid valves are derived from __________. - (Correct Answer) - Fused endocardial
cushions of the AV canal.
Fetal erythropoiesis occurs in ___________? - (Correct Answer) - -Yolk sac (3-8 weeks)
-Liver (6 weeks-birth)
-Spleen (10-28 weeks)
-Bone marrow (18 weeks to adult)
Hemoglobin development - (Correct Answer) - -Embryonic globins: ζ and ε.
-Fetal hemoglobin (HbF) = α2γ2.
-Adult hemoglobin (HbA1) = α2β2.
-HbF has higher affinity for O2 due to less avid binding of 2,3-BPG, allowing HbF to extract O2
from maternal hemoglobin (HbA1 and HbA2) across the placenta.
Fetal circulation diagram - (Correct Answer) -
Correct -Grade A+ Assured.
.
Truncus arteriosus gives rise to __________. - (Correct Answer) - Ascending aorta and
pulmonary trunk
Bulbus cordis gives rise to __________. - (Correct Answer) - Smooth parts (outflow tract) of left
and right ventricles
Endocardial cushion gives rise to? - (Correct Answer) - Atrial septum ,membraneous
interventricular septum; AV & semilunar valves
Primitive atrium gives rise to __________. - (Correct Answer) - Trabeculated (muscular)
portions of the left and right atria
Primitive ventricle gives rise to __________. - (Correct Answer) - Trabeculated (muscular)
portions of the left and right ventricles
Primitive pulmonary vein gives rise to __________. - (Correct Answer) - Smooth part of the
right atrium
Left horn of sinus venosus gives rise to __________. - (Correct Answer) - Coronary sinus
Right horn of sinus venosus gives rise to __________. - (Correct Answer) - Smooth part of the
right atrium (sinus venarum)
,[Type here]
Right common cardinal vein and right anterior cardinal vein gives rise to __________. - (Correct
Answer) - Superior vena cava (SVC)
When does the heart beat begin to beat spontaneously? - (Correct Answer) - -4 weeks of
development
-First functional organ in vertebrate embryos
What is cardiac looping? - (Correct Answer) - -Primary heart tube loops to establish left-right
polarity; begins in week 4 of gestation.
Defect in left-right dynein (involved in L/R asymmetry) can lead to___________, as seen in
Kartagener syndrome (primary ciliary dyskinesia). - (Correct Answer) - Dextrocardia
What is a foramen/ostium? - (Correct Answer) - opening
What is a septum? - (Correct Answer) - wall
Septation of atria (7 Steps) - (Correct Answer) - 1. Septum primum grows toward endocardial
cushions, narrowing foramen primum.
2. Foramen secundum forms in septum primum (foramen primum disappears).
3. Septum secundum develops as foramen secundum maintains right-to-left shunt.
4. Septum secundum expands and covers most of the foramen secundum. The residual foramen
is the foramen ovale.
5. Remaining portion of septum primum forms valve of foramen ovale.
,[Type here]
6. (Not shown) Septum secundum and septum primum fuse to form the atrial septum.
7. (Not shown) Foramen ovale usually closes
soon after birth because of increased LA pressure.
Patent foramen ovale is caused by a failure of __________ and ___________ to fuse after birth.
What can this lead to? - (Correct Answer) - -Caused by failure of septum primum and septum
secundum to fuse after birth; most are left untreated.
-Can lead to paradoxical emboli (venous thromboemboli that enter systemic arterial circulation),
similar to those resulting from an ASD.
Septation of the ventricles (3 steps) - (Correct Answer) - 1. Muscular ventricular septum forms.
Opening is called interventricular foramen.
2. Aorticopulmonary septum rotates and fuses with muscular ventricular septum to form
membranous interventricular septum, closing interventricular foramen.
3. Growth of endocardial cushions separates atria from ventricles and contributes to both atrial
septation and membranous portion of the interventricular septum.
What is the most common congenital cardinal anomaly? - (Correct Answer) - VSD
Most common location of VSD? - (Correct Answer) - The membranous septum
Outflow tract formation - (Correct Answer) - Truncus arteriosus rotates; neural crest and
endocardial cell migrations cause truncal and bulbar ridges that spiral and fuse to form
aorticopulmonary septum to form ascending aorta and pulmonary trunk.
, [Type here]
What are the conotruncal abnormalities associated w/ failure of neural crest cells to migrate? -
(Correct Answer) - Transposition of the greta vessels
Tetralogy of Fallot
Persistent truncus arteriosus
Aortic/pulmonary valves are derived from ____________. - (Correct Answer) - The endocardial
cushions of outflow tract.
Mitral/tricuspid valves are derived from __________. - (Correct Answer) - Fused endocardial
cushions of the AV canal.
Fetal erythropoiesis occurs in ___________? - (Correct Answer) - -Yolk sac (3-8 weeks)
-Liver (6 weeks-birth)
-Spleen (10-28 weeks)
-Bone marrow (18 weeks to adult)
Hemoglobin development - (Correct Answer) - -Embryonic globins: ζ and ε.
-Fetal hemoglobin (HbF) = α2γ2.
-Adult hemoglobin (HbA1) = α2β2.
-HbF has higher affinity for O2 due to less avid binding of 2,3-BPG, allowing HbF to extract O2
from maternal hemoglobin (HbA1 and HbA2) across the placenta.
Fetal circulation diagram - (Correct Answer) -
