Session 3- Development Of CVS

Question 1

Describe the formation of the primitive heart tube

Answer 1

In the mesoderm layer the heart field region arises and the two tubes come together at the mid-line forming a single primitive heart tube

Question 2

Describe the looping of the primitive heart tube

Answer 2

At day 22, the primitive atrium elevates upwards and goes behind the primitive ventricle making it posterior.
Looping of the primitive heart tube gives rise to the transverse pericardial sac in the gap between the arteries and veins,
The oblique sinus is the spaces between the adjacent pericardium

Question 3

Name the regions of the developing heart

Answer 3

Truncus arterioses
Primitive ventricle
Primitive atrium
Sinus venosus

Question 4

Describe the formation of the inter-atrial septum

Answer 4

1) The formation of the endocardial cushion in the atrioventricular canal
2) The septum primom grows halfway between the roof of the primitive heart tube.
3) There’s a gap between between the septum primom and the endocardial cushion called the ostium primom
4) Ostium secondum forms due to apoptosis higher up in the septum
5) The septum primom continues to grow, therefore the ostium primom gets smaller and closes as the septum primom fuses with the endocardial cushion.
6) The septum secondum forms from the roof of the atrial and from the endocardial cushionand forms on the right side and overlaps the ostium secondum

Question 5

Formation of the inter-ventricular septum

Answer 5

1) The muscular component grows upwards from the muscular wall of the primitive ventricle
2) The membranous portion grows downwards from the endocardial cushion
3) the two components fuse and form the inter-ventricular septum

Question 6

Understand the principles of the fetal circulation

Answer 6

1) 3 fetal shunts: 2 that bypass the lungs and one that bypasses the liver as the placenta already provides oxygenated and processed blood
2) Ductos arteriosis: (Major shunt) Connects pulmonary artery to the aorta so the blood goes straight into the systemic circulation without going towards the pulmonary circuit.
3) Forman Ovale: connects the right to the left atrium, bypassing the right ventricle and hence the pulmonary circuit
4) Ductus Venosus: Bypasses the liver as it goes straight towards the inferior vena cava so it’s not processed twice.

Question 7

What happens to the fetal shunts after birth?

Answer 7

When foetus takes their first breathe resistance in the pulmonary circuit drops and the pressures within the left atrium increase and closes foramen ovale.

Question 8

Describe in brief the development of the great vessels?

Answer 8

1) The aorta is formed from the 4th aortic arch
2) The right subclavian artery is formed from the 4th aortic arch
3) The left pulmonary artery is formed from the 6th aortic arch
4) 6th arch on the right degenerates.
5) The ductus arteriosis forms in the 6th aortic arch

Question 9

What is the difference between the course of the left and right recurrent laryngeal nerves in relation to the great vessels?

Answer 9

There’s a difference because in the sixth arch on the right hand side degenerates so the right recurrent laryngeal nerve actually originates higher up in association with the right subclavian artery compared to the left RLM as it has to loop under the aortic arch.

Question 10

Do both the left and right atria develop entirely from structures present in the primitive heart tube?

Answer 10

No.
The smooth portion, where the left atrium develops is from the pulmonary veins.
The rough portion, where the right atrium develops is from the primitive heart tube. (Primitive atrium and venos sinosis)

Question 11

Relate the anatomy of the adult heart to embryonic structuresp

Answer 11

Primitive ventricle- ventricles
Primitive atrium- atrium
Sinus venosus- gives rise to the right atrium and veins?
Truncus arteriosis- The spiral septum within the truncus arteriosis forms the aorta and pulmonary trunk and other great vessels.

Question 12

Describe the common types of congenital malformation of the heart and great vessels

Answer 12

1) Atrial-septal
2) Hypoplastic left heart (single ventricle)
3) Patent ductus arteriosis
4) Transposition of great arteries
5) Tetralogy of fallot

Question 13

Atrial- septal defect

Answer 13

The patent foramen ovale. The septum primom and septum secondum fail to fuse together. If the gap is small, it may not cause an effect in childhood but effects in adulthood.

Question 14

Hypo-plastic left heart

Answer 14

Osteosecondum (gap) is too small, there’s low blood flow from the right atrium to the left atrium.
Left atrium doesn’t receive enough blood therefore the left ventricle doesn’t form.
The right ventricle only.
Treatment: First step: Prevent the Ductus arteriosis from closing
As the right atrium would be deprived from system

Question 15

Patent ductus arteriosis

Answer 15

The ductus arteriosis fails to close

There’s excess of mixing of pulmonary and systemic blood

Question 16

Transposition of great arteries

Answer 16

Swapping of the great arteries
Instead of the the pulmonary trunk coming from the right ventricle and the aorta it comes from the left ventricle
Cause: Spiral septum twists another 180 degrees. This is dangerous as the pulmonary and systemic form separately.
In foetus, shunts allow blood to cross so not a problem
Following birth:
Give drugs to maintain the latency of ductus arteriosis and then surgery to keep it open.

Question 17

What are the group of cardiac defects known as Tetralogy of fallot?

Answer 17

Overriding aorta
Pulmonary stenosis
Right ventricular hypertrophy
Ventricular septal defect

Question 18

What causes the tetralogy of fallot?

Answer 18

• Problem with the spiral septum, it forms eccentric vessels.
• The free edge of the spiral septum doesn’t line up with the endocardial cushion which causes a ventricular septal defect.

Question 19

What is the first consequences

Answer 19

Causes a smaller pulmonary trunk and larger aorta.
Overriding aorta
Causes pulmonary stenosis
Causes right ventricular hypertrophy because it has to work harder to push through the pulmonary trunk.