CVS 6 - Cardiac Embryology (Part 1)

Question 1

NB: This lecture is mostly visual - you need to be able to see this visually, and be able to recognise structures you’ve drawn (see slides)

Answer 1

Yesssirrr

Question 2

When do heart field tubes come together in the midline?

What does this form?

Answer 2

• Roughly at 3 weeks

- this forms 1 singular heart tube (roughly day 22) - pretty much where we start this lecture from.

Question 3

Describe the embryological structure of the heart tube at day 22.

Answer 3

From the arteriole side downwards:

• Truncus arteriosus at the top (arterioles)
• Then have the primitive ventricle swelling beneath the first narrowing of the tube.
• Then have the primitive atria swelling beneath the 2nd narrowing of the tube
• Sinus venosus at the bottom, beneath the 3rd narrowing of the tube. Blood comes in through here.

Question 4

What 2 main things must happen to the heart tube after day 22

Answer 4

1) There must be looping of the tube, as the veins are at the bottom, and most of these vessels must be brought to the top as we see in the adult heart.
2) There must be seperation of the ventricles and atria to form the distinct 4 chambers - done by growth of septa.

Question 5

What occurs during the 1st cardiac looping event?

What occurs during the 2nd cardiac looping event?

Answer 5

• The atrium is elevated, rising up to sit posteriorly behind the ventricle.
• Then get looping into a U-shaped heart tube, with the visceral pericardium folding with it and running along in direct contact with the heart tube.
• There is now a gap between the arteries and veins - called the transverse pericardial sinus (can be seen on adult heart), as well as an oblique sinus which is a space within the pericardial cavity behind the heart.

Question 6

What 2 components of the heart tube forms the adult atrium?

What are the rough and smooth portions of the adult atrium derived from?

Answer 6

1) Primitive atrium –> forming the rough portion of the adult atrium
2) Sinus venosus –> forming the smooth portion of the adult atrium (as well as the SAN).

Question 7

How many aortic arches are there in humans?

What does the aorta and pulmonary arteries form from?

Answer 7

• 5 (1,2,3,4 +6) - 5th aortic arch degenerates in humans.
• both develop from the truncus arteriosus, the 4th arch forms the aorta (aortic arch) and the 6th arch forms the pulmonary arteries.

Question 8

Which recurrent laryngeal nerve sits higher up and why?

Answer 8

• The right recurrent laryngeal nerve sits higher up than the left, as the ductus arteriosus only forms on the left hand side. It loops around the right subclavian artery.
• The left RLN loops around the 6th aortic arch and sits lower down compared to the right, as this portion of the 6th aortic arch degenerates on the right side.

Question 9

What are the 3 foetal shunts in the heart and why are they necessary?

Answer 9

1) Ductus arteriosus
2) Oval foramen
3) Ductus venosus

• Shunts 1+2 allow blood to bypass the lungs, which blood is not required to travel to as the foetus does not breathe air
• Shunt 3 allows blood to bypass the liver, as detoxification is carried out by the placenta.