Heart Development

Question 1

In which week of development does the embryo fold?

Answer 1

4th week

Question 2

What can cause congenital birth defects? (3)

Answer 2

• Genetics
• Exposure to chemicals/drugs/infectious agents
• Unexplained

Question 3

The primitive heart is a tube, what are the names of the sections following the direction of flow?

Answer 3

Sinus venous 
Atrium
Ventricle
Bulbous cordis
Truncus arteriosus
Aortic roots 

At this point there are no barriers within the tube, there is nothing restricting flow

Question 4

What causes the primitive heart tube to fold and loop?

Answer 4

As the tube elongates it runs out of room within the pericardial sac and as a result has to twist and fold up.

The atrium which is the most Caudal part initially is pushed upwards so it becomes approximately the most cranial part.

Question 5

Which mesodermal plate does the heart arise from?

Answer 5

The splanchnic mesoderm

Inferior lateral part of mesoderm

Question 6

What does the R atrium develop from?

Answer 6

The majority of the primitive atrium

Consume part of sinus venosus (inlet tube)

Question 7

What does the left atrium develop from?

Answer 7

Only a small portion of the primitive atrium (which is why it is so smooth)

Most of it is derived from the pulmonary vein which is essentially absorbs (vessel walls are smooth walled which is why the LA itself is smooth walled)

Question 8

Why is it good to have some blood entering the right ventricle during foetal development? What is bad about this? How is this problem resolved?

Answer 8

The RV needs to pump against a small a mount of blood to promote muscle strengthening and normal development.

However this does mean that some blood is then sent on its way along the pulmonary trunk towards the lungs.

There is a shunt called the DUCTUS ARTERIOSUS which connects the pulmonary trunk to the aorta, bypassing the lungs.

Question 9

What is the shunt found between the right and left atria?

Answer 9

Foramen ovale

Question 10

What is the shunt between the placenta and inferior vena cava? Why is it necessary?

Answer 10

Ductus venosus

Needed to bypass the liver because the liver is so metabolically active that it would take all the oxygen and nutrients for itself.

Question 11

How is the foramen ovale closed at birth?

Answer 11

When respiration begins the pressure in the LA increases above that of the right atrium and this causes it to shut. Because the septum primum pushes against the septum secundum.

Question 12

How is the ductus arteriosus closed at birth?

Answer 12

There is a muscle contraction which closes it

Question 13

The great vessels of the heart begin as a bilaterally symmetrical system of arched vessels, which undergo extensive remodelling to create major arteries leaving the heart. What do the 4th and 6th arches give rise to?

Answer 13

4th;
R=proximal part of right subclavian artery
L= arch of aorta

6th;
R= right pulmonary artery
L= left pulmonary artery and ductus arteriosus

Question 14

Why is a hoarse voice the first sign of pathology in the thorax?

Answer 14

Because as the heart descends during development a nerve (that will become the left recurrent laryngeal nerve) hooks around the 6th aortic arch and the ductus arteriosus.
This nerve controls the muscles of the larynx so any impingement on this nerve in the thorax will result in a hoarse voice

Question 15

What occurs if the ductus arteriosus shunt does not close properly?

Answer 15

PDA - patent ductus arteriosus

Persistent communication between the descending aorta and the pulmonary artery.

Blood will shunt left to right

Question 16

How is the foramen ovale formed?

Answer 16

1. Endocardial cushions (formed by neuro-crest cells) form a shelf between all four chambers
2. Septum primum starts to develop (superior to inferior direction)
3. As septum primum forms there is a ostium primum formed (meaning first hole at the base of the septum primum- this later closes)
4. Ostium secundum appears due to apoptosis at the top of the septum primum
5. Ostium secundum completed
6. Septum secundum begins to form in the same was the septum primum did
7. The septum secundum is completed with a hole at the bottom ( like the ostium primum in the septum primum)
8. Foramen ovale is complete- right to left shunt is formed.

blood goes through the hole in the inferior part of the septum secundum and the through the ostium secundum of the septum primum

Question 17

What are the two main causes of atrial septal defects?

Answer 17

Septum primum issues ;

• re-absorbed
• too short

Septum secundum issues;
-to small

**not necessarily an issue in the womb but cause issues after birth.

Question 18

What is hypoplastic left heart syndrome?

Answer 18

Underdeveloped left ventricle

Question 19

What is the cause of hypoplastic left heart syndrome?

Answer 19

Exact cause not known, but there are theories

1. Defect in development of mitral and aortic valves, which results in atresia (absence or abnormal narrowing of the valve) which causes limited flow
2. Ostium secundum is too small which results in inadequate right to left flow in utero.

Both these theories would result in the disuse of the left ventricle, meaning it does not develop properly and/or is underdeveloped.