8C · VR Systemic Vasculature Tour

This lecture is a VR walkthrough in three short videos. It uses MRI and CT scan images to visualize at least some of the larger arteries and veins of the systemic circulation, and to see where different arteries branch off to feed the vascular beds of lecture 8A. There are no slides.

The coronary circulation¶

The first stop is on the heart scan, because the very first vessels that branch off the aorta are the ones that feed the heart. They branch off almost immediately after the aorta leaves the aortic valve. Coming down the aorta toward the heart, the three cusps of the aortic valve come into view. Come down too far and you are in the left ventricle, so come back up just far enough, and the highlighted coronary arteries come off just above the valve cusps.

Right coronary artery. On the side of the right ventricle, as you would predict from the name. It comes off and branches around the side of the heart to feed the front and the back of the right side of the heart.

Left coronary artery. It comes off a little higher, and divides. One fork runs right down the front of the heart: the left anterior descending artery. It is nicknamed the widow maker artery, because this is where clots, clogs, and atherosclerotic plaques so often form, plugging the vessel and preventing blood from flowing from the aorta down to perfuse the heart muscle. A lot of heart attacks occur in this artery. The other fork is the circumflex artery, which wraps around the left side of the heart and can be traced around the back. From there the arteries branch into smaller and smaller vessels, with a lot of vessels covering the back surface of the heart.

Cardiac veins. On the back of the heart, the largest veins come up the side of the left ventricle and pull into the great cardiac vein. From there, all the veins eventually merge into a large one across the back, the coronary sinus, which dumps directly into the right atrium. It has its own entrance into the right atrium, separate from where the inferior vena cava comes in. This is where the veins of the heart all eventually drain.

From inside the aorta. Coming in from the back of the aorta, sitting right at the aortic valve with its cusps, you can see where the right and left coronary arteries come off. They leave from little pockets right behind where the valve flaps open up, called the aortic sinuses. This is literally the first arterial branching off the aorta.

The systemic arteries¶

The second video uses a CT scan of a torso, from the bottom of the jaw and the neck, out to the shoulders, through the chest and abdomen, and down into the legs. Carving away the rest of the scan reveals the major arterial tree. The aorta comes out of the heart, with the two coronary arteries coming off it (not well defined on this scan). Then comes the ascending aorta, the big aortic arch, and the aorta coming back down over the arch.

Three major branches come off the aortic arch:

1. Brachiocephalic trunk. Feeds the head, neck, arm, and shoulder on the right side of the body. It breaks into the cephalic branch, meaning head: the right carotid artery, heading up the right side of the head to perfuse the brain, one of the avenues of cerebral perfusion. It also gives the artery out into the arm and shoulder, the subclavian artery, which supplies the skin and musculature there and later branches into the brachial artery, radial artery, and others.

2. Left common carotid artery. Goes up to feed the left side of the head, neck, and brain. Cerebral perfusion again.

3. Left subclavian artery. Heads out to perfuse the left arm and shoulder.

Coming down, the aorta hugs along the back of the body, and several branches come off it:

• The top branch goes over to the liver, stomach, and spleen. A lot of this is splanchnic, or gut, circulation.

• The next branch, the superior mesenteric artery, is splanchnic as well, and goes out to feed a bunch of the intestines.

• Toward the back, the renal arteries run to a kidney on either side, feeding the renal circulation.

• Down through the lower abdominal cavity and the pelvis, the aorta splits into the common iliac arteries. The external iliac arteries go down into the femoral arteries to feed the legs. This is the major artery perfusing the musculature and skin of the legs, the skeletal muscle and cutaneous circulations.

Putting the body back in for context: the pelvic cavity, the kidneys, the liver, spleen, and stomach, the heart, the carotids coming up the neck toward the brain, and the subclavian and brachial arteries heading out toward the arms and shoulders.

The systemic veins¶

The third video covers veins. Cutting away the tissues to look at the framework of the veins alone, notice how closely the pattern mirrors the arteries. The arteries originated in the heart and branched outward. The veins originate out in the periphery and merge inward, but they track the same path.

• Just as femoral arteries go out, femoral veins come in.

• Just as iliac arteries lead out, iliac veins lead in.

• The inferior vena cava runs right alongside the aorta.

• Renal veins sit right next to the renal arteries.

• Snake-like, branching gastrointestinal, or splanchnic, veins all lead into the liver and then out into the inferior vena cava.

• Just as the carotid arteries go up, the jugular veins come down from the head, draining the cerebral circulation.

• The subclavian veins come in from the arms and shoulders, draining the blood that fed the skin and skeletal muscle there. Where they join the jugulars, we get the brachiocephalic veins.

Around the heart, watch the aorta and the vena cava. The ascending aorta comes out, comes over, and heads down through the thoracic cavity, with the vena cava beside it. As you move down, the two move closer together and soon start tracking together, all the way down until they branch in the pelvis. When sister arteries and veins sit at similar levels of branching on their respective sides of the circulation, they tend to run next to each other.

Renal artery against renal vein. Even when arteries and veins run next to each other at similar levels of branching, the veins always have a larger lumen. That is visually striking at the kidneys. The renal arteries run behind the renal veins, so the scan is flipped to come in from the back, cutting through the ribs, the vertebral column, and the kidneys. On each side, a tiny gray renal artery sits in front of a much larger blue renal vein.

So the veins parallel the arteries in their branching patterns, and these scans show where we drain the cerebral circulation, some of the muscle and skin circulation from the arms and shoulders and from the legs and feet, the renal circulation, and the splanchnic circulation.