Lecture 22: Great Vessel Embryology

Question 1

How is the first aortic arch formed?

Answer 1

Dorsal aorta connects to the developing heart tubes in the aortic sac

Question 2

What does the dorsal aorta form?

Answer 2

Aortic arches I - VI and intersegmental arteries

Question 3

How are the intersegmentals connected?

How is the vertebral artery formed?

Answer 3

• New anastomosis (future vertebral artery) forms vertically and connects all the intersegmental arteries.
• cervical intersegmentals degenerate and leave the anastomosis to connect the arteries

Question 4

How is the internal thoracic artery formed? What branches from it?

Answer 4

Embryo folds and the thoracic segment of the vertical anastomosis is placed on the anterior thoracic wall, eventually becoming the internal thoracic a.
-Posterior and anterior intercostal arteries branch from this

Question 5

What does the 5th lumbar intersegmental artery eventually form?

Answer 5

Common Iliac A.

Question 6

What else happens at the 5th lumbar intersegmental artery?

Answer 6

A new anastomosis forms that connects to the umbilical artery (originating from the dorsal aorta). Proximal part of the umbilical artery will degenerate after this is formed.

Question 7

At the remaining segment of the umbilical artery, what branches form?

Answer 7

Superior vesicular a. branches out to feed the superior bladder

Question 8

After birth, what happens to the segment of the umbilical artery distal to the superior vesicular a. branch?

Answer 8

Becomes the umbilical ligament

Question 9

At what level do both dorsal arteries fuse?

Answer 9

At T4 via the 6th aortic arch

Question 10

What happens to the first aortic arch?
Second aortic arch?
Fifth aortic arch?

Answer 10

• degenerates as more vasculature develops and it becomes less important
• also degenerates

Question 11

What happens to the 3rd aortic arch?

Answer 11

After the 1st and 2nd aortic arches degenerate, the dorsal aorta meeting the 3rd arch becomes the Internal Carotid A.
Another branch grows upward direction medial to the ICA on the 3rd arch and becomes the ECA

Question 12

What happens to dorsal aorta after carotids form?

Answer 12

Part that connects 3 and 4 will degenerate

Question 13

What happens to the left 4th aortic arch?

Answer 13

Left side contributes to the aorta with the aortic sac, dorsal aorta and 7th cervical intersegmental a

Question 14

What happens to the right 4th aortic arch?

Answer 14

Merges with 7th cervical intersegmental artery to form the right subclavian artery

Question 15

What becomes the brachiocephalic trunk? What becomes the left subclavian artery?

Answer 15

• left 4th aortic arch

- 7th cervical intersegmental artery

Question 16

What happens to the left 6th aortic arch?

What happens to the right 6th aortic arch?

Answer 16

• Segment distal to the pulmonary connection degenerates, but leaves the ductus arteriosus
• same, but leaves no ductus arteriosus

Question 17

Why is the branching of the Vagus N. higher on the right than the left?

Answer 17

No ductus arteriosus forms on the right side, so when Vagus develops its laryngeal branch, it has nothing to “hook” on to on the right side

Question 18

Where does fetal circulation get nutrients?

Answer 18

Placenta, where it mixes with maternal blood

Question 19

Describe the flow of fetal circulation in the IVC:

Answer 19

Body > Umbilical artery > Placenta > umbilical vein > ductus venosus to bypass the liver > IVC > RA > foramen ovale > LA > LV> ascending aorta > head and UE

Question 20

Describe the flow of fetal circulation in the SVC:

Answer 20

Body > placenta > umbilical artery> SVC > RV and patent ductus arteriosus where it mixes with oxygenated blood and bypasses the lungs > descending aorta > LE

Question 21

How does the ductus arteriosus close after birth?

Answer 21

Maternal prostaglandins keep it open in-utero. After birth, no more maternal prostaglandins > contracts and closes

Question 22

What happens if ductus arteriosus remains patent? What is the main consequence of this?

Answer 22

• DA is a hole between the pulmonary trunk and aorta in utero
• Lungs inflate causing decrease in TPR and pressure in the pulmonary trunk. Blood from higher pressure aorta wants to flow into lower pressure pulmonary trunk, so oxygenated blood mixes with non-oxygenated blood.
• Left ventricle is losing oxygenated blood to the pulmonary trunk and has to work harder to keep CO consistent = hypertrophy

Question 23

What are aortic coarctations?

What condition is this most common in?

Answer 23

• Restrictions in the aorta because certain parts did not grow
• Turner’s syndrome

Question 24

Post ductal coarctation vs. Pre ductal coarctation

Answer 24

Post: Restriction is after the ductus, so no blood enters the lower limb since both sources are blocked
Pre: Restriction is before the ductus, so blood from the ductus can still supply the lower limb

Question 25

How does the body compensate in post ductal coarctation?

Answer 25

Larger thoracic arteries to try and bypass the upstream restriction

Question 26

What causes an aberrant origin of the right subclavian artery? What symptoms can this cause?

Answer 26

• Right 4th arch and Right 7th intersegmental arteries disappeared. Retained the dorsal aorta portion that needed to degenerate.
• Usually asymptomatic, but can have dysphagia

Question 27

What causes a double aortic arch?

What symptoms does this cause?

Answer 27

• dorsal aorta segment remains but the rest develops normally.
• Tracheal strangulation, dysphagia and dyspnea

Question 28

What causes an interrupted aortic arch?

How can this be treated?

Answer 28

• Both Right and left 4th arches disappear so there is no oxygenated blood going to the LE
• keep ductus arteriosus open

Question 29

What happens to the vitelline veins?

Answer 29

Superior part: As liver buds grow, they become hepatic sinusoids by the liver.

Inferior parts:
Proximal left vitelline vein degenerates
Distal right vitelline vein degenerates

Question 30

What happens to the umbilical veins?

Answer 30

Right: degenerates after ductus venosus forms diagonially from right to left
Left: remains as left umbilical vein and connects to ductus venosus that bypasses the liver

Question 31

How do the brachiocephalic veins form?

Answer 31

Right and left anterior cardinal veins are connected by anastomosis.
Anastomosis - left brachiocephalic v.
Right anterior cardinal v - Right brachiocephalic v.

Question 32

What causes abnormal superior vena cava?

Answer 32

Anastomosis between the anterior cardinal veins did not form so right anterior cardinal vain connects with left sinus horn (future coronary sinus) instead, forming 2 SVCs