Lecture 4 2020 Cardiology 2 vascular

What are the two processes by which the vascular system forms?

Vasculogenesis and angiogenesis.

What are vasculogenesis and angiogenesis?

Vasculogenesis is the formation of blood vessels de-novo. The heart and great vessels form by vasculogenesis. Angiogenesis is the formation of new vessels from existing vessels and is the process responsible for vascular development in the newly forming organ and tissue systems.

What are the three paired sets of veins initially present, and what do they drain?

• Cardinal veins (anterior and posterior) drain the head and body wall;

• Vitelline veins drain the yolk sac;

• Umbilical veins bring blood to the fetus from the placenta.

Where do all three sets of veins flow?

All three sets of veins on each side flow into the right and left horns of the sinus venosus.

How does the arterial system develop?

• The arterial system develops from aortic arches that arise from the aortic sac. These arches form the dorsal aortae and supply blood to the head and body wall.

• The dorsal aortae give off the vitelline and umbilical arteries.

How do the aortic arches develop?

The aortic arches develop from the vasculature of the pharyngeal arches. There are 5 aortic arches (I–VI, V never forms), that develop cranial to caudal.

What happens to the cranial arches as the caudal arches are forming?

The cranial arches develop, regress, and degenerate even as the caudal arches are forming.

What happens to the aortic arches as the vascular system develops?

The aortic arches regress by programmed cell death into the definitive pattern. There is asymmetry, particularly in the positions of the vagus nerve and its laryngeal branches.

What are the derivatives of the aortic arches?

This tells you which artery forms from which arch

1: Maxillary artery
2: Stapedial, hyoid
3: Carotid system
4L: Arch of aorta
4R: Subclavian
5: Disappears
6: Pulmonary arteries and ductus arteriosus (L)

What do the vitelline and umbilical arteries form?

• The vitelline arteries fuse and form the arteries of the dorsal mesentery (celiac and superior mesenteric arteries).

• The umbilical arteries form the inferior mesenteric, internal iliac, and vesicular arteries.

Where do the coronary arteries derive from?

The coronary arteries derive from the epicardium and cells of the sinus venosus. They are not derivatives of the primordial aortic arch system.

What are the three paired sets of veins initially and what do they drain?

• Cardinal veins (anterior and posterior) drain the head and body wall;

• Vitelline veins drain the yolk sac;

• Umbilical veins bring blood from the placenta.

All three sets of veins on each side flow into the right and left horns of the sinus venosus.

What happens to the vitelline veins and proximal portions of the umbilical veins?

Vitelline veins along with proximal portions of the umbilical veins degenerate and contribute to formation of the hepatic sinusoids by about 5 weeks.

How does the ductus venosus form and what is its function?

Further degeneration, and combination, of the right umbilical and vitelline veins results in formation of the ductus venosus.

• The ductus venosus is a connection between the left umbilical vein and the right hepatocardiac channel that allows umbilical blood to bypass the liver.

• It has a valvular structure that allows it to autoregulate and respond to changes in maternal blood flow.

What happens to the remainder of the vitelline veins?

The remainder of the vitelline veins coalesce to form the mesenteric veins and the portal venous system.

What do the cardinal veins ultimately form?

The cardinal veins undergo similar combination and regression to ultimately form the veins draining the head, body wall and kidneys. The anterior cardinal veins form the jugular venous system, and the right common cardinal vein becomes the superior vena cava (SVC).

What happens to the posterior cardinal veins, and what do the subcardinal and supracardinal veins become?

The posterior cardinal veins degenerate, and new veins (subcardinal and supracardinal) form. The sub- and supra-cardinal veins become the renal, iliac, and azygous systems, respectively. The arterial system tends to form along the left side of the body axis as it regresses, while the venous system aligns to the right side.

How does the placenta form and participate in exchange?

As the embryonic venous system is forming, so is the placenta. The cytotrophoblast overtakes the syncytial trophoblast and forms villi that develop vascular structures that participate in gas (O₂ and CO₂) and nutrient exchange.

What is coarctation of the aorta and what are its two types?

Coarctation of the aorta is relatively common and can pass unnoticed until adulthood, when a patient presents with labile HBP. Two types can occur: pre- and post-ductal.

What is associated with preductal and postductal coarctation?

Preductal is usually associated with patent ductus arteriosus. In postductal, large collaterals form from intercostal and thoracic arteries.

What causes an abnormal origin of the right subclavian, and what happens as a result?

Abnormal origin of the right subclavian occurs when the right 4th arch abnormally obliterates. The right subclavian crosses the midline constricting the esophagus.

What causes a double aortic arch and what does it form?

Double aortic arch occurs when the right dorsal aorta persists. This forms a vascular ring around the trachea and esophagus.