CVS- Embryology 2

Transcript

Host1:Alright everyone, welcome back to CVS Embryology, part two. Today's focus: the development of the heart and blood vessels.

Host2:Good morning, Doctor. So, we're diving into the formation of our major arteries and veins, right?

Host1:Exactly. We'll cover large arteries, especially aortic arches, main veins, fetal circulation, and those important congenital malformations.

Host2:Okay.

Host1:Let's start with aortic arches. Remember, these are short vessels connecting ventral and dorsal aortae, running within the pharyngeal arches.

Host2:Right, six pairs forming around the fourth and fifth week. But the first, second, and fifth pairs are transient and disappear quickly, don't they?

Host1:Precisely. The first leaves a small portion for the maxillary artery, and the second contributes to the hyoid and stapedial arteries. What about the third arch?

Host2:The third is symmetrical. It gives rise to the initial internal carotid artery, and the common carotid comes from the ventral aorta.

Host1:Excellent. Now, the fourth aortic arch is key. Its ultimate fate is different on the right and left side.

Host2:On the left, it forms a part of the arch of the aorta. On the right, it forms the proximal segment of the right subclavian artery.

Host1:Perfect. And the sixth? The pulmonary arch?

Host2:It branches to the lung buds. On the right, its proximal part is the right pulmonary artery, and the distal part disappears. On the left, the distal part persists as the ductus arteriosus during fetal life, and the proximal part forms the left pulmonary artery.

Host1:Very good. Moving on, quickly, vitelline arteries fuse and form the celiac, superior mesenteric, and inferior mesenteric arteries. Umbilical arteries, initially paired, connect to the common iliac. After birth, proximal parts become external and internal iliacs, while distal parts form the medial umbilical ligaments.

Host2:So, vitelline for the gut, umbilical for fetal circulation and then ligaments.

Host1:Exactly. Now, the venous system. We're looking at vitelline, umbilical, and cardinal veins.

Host2:The vitelline veins form the portal vein and contribute to the IVC. The left vitelline vein disappears.

Host1:Correct. Umbilical veins: the right and proximal left disappear. The distal left umbilical vein remains, carrying blood from the placenta to the liver, forming the ductus venosus to bypass the liver's sinusoidal plexus. Both obliterate after birth.

Host2:And the cardinal veins, through anastomoses, channel blood to the right, forming the SVC and various segments of the IVC.

Host1:Precisely. Now, let's trace fetal blood circulation. From the placenta, well-oxygenated blood is conducted to the fetus via the umbilical vein. What happens next?

Host2:Most bypasses the liver via the ductus venosus directly into the inferior vena cava.

Host1:Good. Where does the inferior vena cava blood go?

Host2:It enters the right atrium, then largely through the foramen ovale into the left atrium, mixing with pulmonary vein blood. From there, it passes into the left ventricle and leaves via the ascending aorta.

Host1:And the small volume of oxygenated blood that remains in the right atrium?

Host2:It mixes with deoxygenated blood from the superior vena cava, passes into the right ventricle, and leaves via the pulmonary trunk. But since the lungs are collapsed...

Host1:High pulmonary vascular resistance...

Host2:...most of that blood passes through the ductus arteriosus into the aorta, bypassing the lungs.

Host1:Excellent. So, three shunts are in the fetal blood circulation?

Host2:Ductus venosus, foramen ovale, and ductus arteriosus. They obliterate or close functionally at birth to become ligaments or a closed foramen.

Host1:Finally, clinical correlates. Patent ductus arteriosus, coarctation of the aorta, abnormal origin of the right subclavian artery, double aortic arch... these are all consequences of abnormal development we've just discussed.

Host2:It's fascinating how understanding the embryology helps explain these congenital malformations.

Host1:Indeed. It's crucial for diagnosis and treatment. Alright, that covers the development of the heart and blood vessels. Any final questions?

Host2:No, Doctor, that was very clear. Thank you!

Host1:You're welcome. Keep reviewing those diagrams.