Primer 8 - Cardiac Embryology

Question 1

What divides the right and left atria?

Answer 1

Septum primum and septum secundum.

Question 2

How is blood shunted from the right atrium to the left atrium in an embryo?

Answer 2

Through the foramen ovale (of the septum secundum) and ostium secundum (of the septum primum).

Question 3

What are the 3 possible causes of an atrial septal defect?

Answer 3

1. Ostium secundum overlaps foramen ovale.
2. Absence of septum secundum.
3. Neither septum secundum nor septum primum develop.

Question 4

What structure grows to close the opening/canal between the atrial chamber and ventricular chamber into two smaller opening?

Answer 4

1. Superior endocardial cushion.

2. Inferior endocardial cushion.

Question 5

What genetic abnormality is commonly associated with endocardial cushion defects?

Answer 5

Trisomy 21.

Question 6

Outline the pathway by which the heart tube forms the atria of the four-chambered heart.

Answer 6

1. Tube grows, elongates and folds into an S-shape.
2. Atrial chamber lays posteriorly in S, and ventricular chambers lays anteriorly in S.
3. Atrial chambers grows and incorporates into superior vena cava and pulmonary veins.
4. Septum primum forms from the middle top dividing the atrias, down to the endocardial cushion that sits in the middle of the heart, but not touching the cushion, leaving a hole called ostium primum.
5. Cell death in septum primum forms a hole called ostium secundum in the superior part of the septum priumum. This forms as the septum primum finally reaches the endocardial cushion.
6. Septum secundum forms incompletely right next to septum primum (leaving a hole called foramen ovale in the inferior part of the septum secundum).

Question 7

Outline the pathway in which the ventricles and their outflow tracts are separated.

Answer 7

1. Ventricular chamber lays anteriorly in the S-shaped heart tube. This leads to muscular ventricular septum to form, dividing the ventricles.
2. Truncoconical swellings (ridges) of the truncus arteriosus meet, fuse and zip (both superiorly and inferiorly) in a 180 degree turn to form the spiral spetum (AKA aorticopulmonary septum).
3. Inferior portion of spiral septum meets with muscular ventricular septum to divide the ventricles and form the aorta and pulmonary arteries.

Question 8

Name 6 different truncoconical (spiral) septum defects.

Answer 8

1. Fenestrae.
2. Ventricular septal defect (VSD).
3. Tetralogy of Fallot.
4. Persistent truncus arteriosus.
5. Transposition of the great vessels (RV to aorta, LV to PA(pulmonary artery))-Because the 180 degree spin did not take place.
6. Dextrocardia.

Question 9

Describe how the ventricles are remodeled in order to form the atrioventricular valves.

Answer 9

1. Myocardium erodes, leading to enlarged ventricles, which makes residual mesodermal tissue becomes fibrous and forms chordae tendinease.
2. Formation of papillary muscles and AV valves.

Question 10

What does the truncus arteriosus become?

Answer 10

Gives rise to the great vessels: the proximal aorta and the proximal pulmonary trunck.

Question 11

What does the bulbus cordis become?

Answer 11

The outflow track of both the right and left ventricles, the smooth parts of the ventricles.

Question 12

What does the primitive ventricle become?

Answer 12

It becomes the trabeculated parts of the ventricles, the muscular parts.

Question 13

What does the primitive atrium gives rise to?

Answer 13

Gives rise to the trabeculated part of both the atrias.

Question 14

What does the sinus venosus turn to?

Answer 14

The left horn of the sinus venosus gives rise to coronary sinuses.
The right horn of the sinus venosus gives rise to smooth part of the right atrium.

Question 15

What does the 1st aortic arch become?

Answer 15

Part of the maxillary artery.

Question 16

What does the 2nd aortic arch become?

Answer 16

2 things:

1. Stapedial artery
2. Hyoid artery

Question 17

What does the 3rd aortic arch become?

Answer 17

It becomes two things:

1. Common carotid.
2. Proximal part of internal carotid.

Question 18

What does the 4th aortic arch become?

Answer 18

The left part: Arch of adult aorta.

The right part: Proximal part of right subclavian artery.

Question 19

What does the 5th aortic arch become?

Answer 19

Nothing.

Question 20

What does the 6th aortic arch become?

Answer 20

It becomes two things:

1. Proximal part of pulmonary arteries.
2. Ductus arteriosus.

Question 21

Which blood vessels carries oxygenated blood from the placenta to the fetus?

Answer 21

The umbilical vein. Veins carry blood back to the heart, notwithstanding the amount of oxygen.

Question 22

What do we give to keep the PDA open?

Answer 22

Prostaglandins.

Question 23

What do we give to close a PDA?

Answer 23

NSAID like endomethacin.

Question 24

Where embryological structure gives rise to the superior vena cava?

Answer 24

The right common cardinal vein and the right anterior cardinal vein.

Question 25

What structure divides the truncus arteriosus into the aortic and pulmonary trunks? What is the cellular origin of this structure?

Answer 25

Aorticopulmonary septum. It is derived from the neural crest derivatives.

Question 26

Which fetal vessel has the highest oxygenation?

Answer 26

Umbilical cord > Ductus venosus > Inferior vena cava > Right atrium.

Question 27

What causes the ductus arteriosus to close?

Answer 27

Breathing. It increases oxygenated blood in aorta which leads to lower levels of prostaglandins, stopping the source that dialates the blood vessels.

Question 28

What causes the foramen ovale to close?

Answer 28

Breathing. It decreases pulmonary resistance which leads to increase in left atrial pressure.