Session 3: Cardiovascular System - Embryology 2

Question 1

After looping of the heart tube. What happens next?

Answer 1

Septation

Question 2

What is septation?

Answer 2

It division of the primitive heart tube in order to create the 4 chambers and selective outflow. Interatrial septum Interventricular septum Septation of ventricular outflow tract

Question 3

Explain development of the inter-atrial septum.

Answer 3

At this time the heart is still the tube. Endocardial cushions will now develop and grow from each side (dorsal and ventral) towards one another. This will divide the developing heart into right and left channels.

Question 4

Explain atrial septation.

Answer 4

Division of the common atrium (1 atrium) into two. It involves formation of two septa with 3 holes.

Question 5

Which are the two septa?

Answer 5

Septum primum and septum secundum.

Question 6

Which are the three ‘holes’?

Answer 6

Ostium primum Ostium secundum Foramen ovale

Question 7

Explain formation of foramen ovale.

Answer 7

Septum primum grows down towards the fused endocardial cushions. Ostium primum is the hole present before the septum primum fuses with the endocardial cushion. Before ostium primum closes a second hold called ostium secundum will appear in the septum primum. Septum secundus will start to form. There is a hole in septum secundum which is foramen ovale.

Question 8

What is fossa ovalis?

Answer 8

The adult remnant of the shunt used in utero to by-pass the lungs.

Question 9

What is the role of septum primum and septum secundum in mature circulation?

Answer 9

When pLA>pRA once a baby takes its first breath septum primum will start pushing against septum secundum and close foramen ovale.

Question 10

What is an atrial septal defect?

Answer 10

When the septa between the atrium didn’t develop correctly.

Question 11

Causes of atrial septal defect.

Answer 11

Septum primum is resorbed or too short. or Septum secundum is too small.

Question 12

What direction will the blood flow in atrial septal defect?

Answer 12

From left atrium to right atrium due to higher pressure in left atrium.

Question 13

Explain hypoplastic left heart syndrome.

Answer 13

Cause is unknown but there are embryological speculations. There might be defect in. development of mitral and aortic valves. Ostium secundum is too small so the right to left flow is inadequate in utero. This leads to underdeveloped left heart.

Question 14

Explain ventricular septation.

Answer 14

It starts with one single ventricular chamber like in atrial septation.

The ventricular septum forms which has 2 components.

A muscular** septum and a **membranous septum.

The muscular portion forms most of the septum and grows upwards towards the fuse endocardial cushions in contrast to septum primum in the atrium which grows downwards.

Question 15

The muscular portion grows upwards but will leave a small gap between the ventricles.

How does this small gap close?

Answer 15

The membranous portion of the interventricular septum is formed by connective tissue and will fill in the gap that the muscular portion left behind.

Question 16

Most common cause of ventricular septal defect.

Answer 16

That the membranous portion doesn’t fill in the gap properly.

Question 17

Direction of flow in ventricular septal defect (VSD).

Answer 17

From the left ventricle to the right ventricle.

Question 18

How is division of the outflow achieved? I.e. making oxygenated blood go where it’s supposed to and oxygen-depleted where it should.

Answer 18

By septation of the outflow tract.

Question 19

Explain septation of the outflow tract.

Answer 19

Truncus arteriosus is the main artery still and hasn’t been divided into the aorta and the pulmonary trunk.

Endocardial cushions will also appear in the truncus arteriosus. As they grow towards each other they twist around each other to form a spiral septum. This is called the aorticopulmonary septum.

The ventral wall of the right ventricle and truncus arteriosus is removed and two distinct arteries form. The pulmonary trunk and the ascending aorta.

Question 20

When do congenital heart defects occur?

Answer 20

When there is a structural defect of the chambers or vasculatures.

When there is an obstruction.

When there is communication between pulmonary and systemic circulations.

Question 21

What is transposition of the great arteries?

Answer 21

When the aorta arises from the RV and the pulmonary trunk arises from LV.

Question 22

Complication of transposition of the great arteries.

Answer 22

Cyanosis and quick death if not corrected.

Question 23

Treatment of transposition of the great arteries.

Answer 23

Prostaglandin is given to ensure ductus arteriosus keeps open. This leads to oxygenated blood to still go out in systemic circulation.

However this is only a quick fix and surgery will be needed as soon as possible.

Question 24

Tetralogy of fallot.

Answer 24

Large ventricular septal defect (VSD)

Overriding aorta (coarctation of aorta)

Pulmonary stenosis

RV hypertrophy

Question 25

Complication of tetralogy of fallot.

Answer 25

Cyanosis. The pulmonary stenosis and the RV hypertrophy will increase the pressure in the right side of the heart.

This along with the large VSD will cause blood to flow from the right ventricle into the aorta. This leads to an overriding aorta where both ventricles pump into aorta and even less to pulmonary system.

This all leads to cyanosis.