Hello. Welcome to Byte Size Med. This video is on the blood supply of the heart.
The heart pumps arterial blood to every part of the body and receives venous blood from all of them. But the heart tissue itself obviously needs blood and it gets that through coronary vessels. The coronary arteries carrying oxygenated blood supply the heart and after exchange, the heart uses what it wants and the cardiac veins carry the deoxygenated blood back to the right atrium.
So first let's look at the coronary arteries. There are two coronary arteries that emerge from swellings called the aortic sinuses, near the aortic valve. There are actually three sinuses: right, left and posterior.
The right coronary artery comes from the right aortic sinus and the left coronary artery from the left aortic sinus. Pretty straightforward. The posterior one doesn't have a coronary artery, so it's also called the non-coronary aortic sinus.
These vessels are going to circle the heart like a crown, and that's why they're called coronary. They go all the way around the front and the back of the heart. So when I draw them, the continuous line means it's going down the front, and the broken line means it's on the back.
A quick recap from part one where we looked at the external features of the heart. Now this is the right atrium, the right auricle, the right ventricle, and the left ventricle. Peeking up here is the left auricle, continuing on the back as the left atrium.
So on the back this would be the right atrium, the left ventricle and a small portion here is the right ventricle. Between the chambers there are grooves or sulci. There are three important ones.
The largest is between the atria and the ventricles. It's called the coronary sulcus. The other two are interventricular sulci.
Interventricular, between the ventricles. There's an anterior interventricular sulcus down the front and the posterior interventricular sulcus down the back. These sulci hold the important vessels.
The arteries that supply the heart and the veins that drain it. After the left ventricle contracts and pumps blood into the aorta, blood recoils and fills up the aortic sinuses. This forces blood through the right and left coronary arteries, since they originate here.
Let's start with the right coronary artery. So it emerges from the right aortic sinus, then it travels between the right auricle and the ascending aorta. It gives off one branch to an important structure here, that's the Sinoatrial node.
Now most of the time the Sinoatrial artery comes from the right coronary artery. But there can be variations, like it could come from the left coronary artery on occasion. But I'm just going to be talking about the common arrangement.
All vessels can have variations. The right coronary artery then travels through the coronary sulcus, in a groove between the right atrium and the right ventricle. Once it reaches the inferior margin, that's this margin here, it gives off another branch.
It's at a margin, gives off a marginal artery called the right marginal artery, which goes towards the apex of the heart. Then the right coronary artery goes posteriorly. So on the back of the heart, it's still in the coronary sulcus, and it gives off another branch to the atrioventricular node.
Then finally it ends with a big branch, called a posterior interventricular artery. This vessel is in the posterior interventricular sulcus. Those are the main branches of the right coronary artery.
Next up we have the left coronary artery. So that emerges from the left aortic sinus. It travels behind the pulmonary trunk and emerges between the trunk and the left auricle.
That's when it divides into two branches, the circumflex artery and the anterior interventricular artery. So the posterior interventricular artery is from the right coronary artery, and the anterior one is from the left coronary artery. The circumflex artery travels along the coronary sulcus, and it can give off another marginal artery called the left marginal artery at the margin.
The anterior interventricular artery is also called the left anterior descending artery. The LAD, and that's an important vessel. It travels downwards in the anterior interventricular sulcus and along this path, there are diagonal branches.
One thing we're expected to know is the distribution of these vessels and what parts of the heart they supply. It's messy to remember, but I'm going to show you a simple version that I use, that you can use as a starting point. We have the right and left coronary arteries.
First I'm going to write down the chambers. So we have the right atrium, the left atrium, the right ventricle and the left ventricle. Between the atria is the interatrial septum.
Between the ventricles is the interventricular septum. The interventricular septum is big. So let's divide it, but not equally.
We have an anterior two-third and a posterior one-third. The conduction system starts with the sinoatrial node, then the atrioventricular node, the atrioventricular bundle and the bundle branches. Now the right coronary artery obviously supplies the right atrium and the right ventricle, but also the interatrial septum.
It Supplies the posterior one-third of the interventricular septum, because remember the posterior interventricular artery comes from the right coronary artery. It also supplies the sinoatrial node and the atrioventricular node. It goes above and beyond what it's expected to do by supplying the left heart as well.
So a little bit of the left atrium, and a little bit of the left ventricle is also supplied by the right coronary artery. The rest of these two chambers is obviously from the left coronary artery, as is the anterior two-thirds of the interventricular septum, because remember that the anterior interventricular artery comes from the left coronary artery. The atrioventricular bundle and the bundle branches are also usually supplied by the left coronary artery.
It also supplies a little bit of the right ventricle. Like I said, there can be variations in how vessels branch and what they supply. This is just the usual distribution.
It's a starting point, it can get more detailed than this but I hope it helps you out. One of the most important variations comes with the origin of this vessel here, the posterior interventricular artery. It determines something called dominance.
It mostly arises from the right coronary artery, that's right dominant. But if it arises from the left coronary artery, that's left dominant. The arteries have now supplied the heart.
The heart uses what it wants, and after exchange, the veins have to carry the deoxygenated blood back to the right atrium. The important veins actually accompany the arteries in the sulci. The anterior interventricular artery is accompanied by the great cardiac vein.
That's in the anterior interventricular sulcus. Once it turns round onto the back of the heart, it accompanies the left circumflex artery. It enlarges to form the coronary sinus, which is located at the base of the heart.
So the posterior surface, in the coronary sulcus, between the left atrium and the left ventricle is occupied by the coronary sinus. The posterior interventricular artery is accompanied by the middle cardiac vein. This is in the posterior interventricular sulcus, again draining into the coronary sinus.
The small cardiac vein is in the coronary sulcus, accompanying the right coronary artery, and also reaching the coronary sinus. These are the three most important veins. The great, middle and the small cardiac veins.
But there are others. Like the posterior cardiac vein, or the anterior veins of the right ventricle, or the right marginal vein. There is an oblique vein of the left atrium.
Now I'm only including this because it actually shows up in embryology. So there are others, but I just covered the most important ones. There are Venae cordis minimae or thebasian veins.
These are also called the smallest cardiac veins, different from the small cardiac vein. These are the smallest cardiac veins. Now these can drain directly into any of the chambers of the heart, including occasionally the left atrium or the left ventricle.
They are bringing deoxygenated blood and they are supposed to be entering the right heart. But if they enter the left, they can contribute to mixing of oxygenated and deoxygenated blood. These are anatomical shunts and I'll talk about that more in pulmonary circulation.
If we were to take just the important stuff, and schematicize this, we've got the right and left aortic sinuses, with the right and left coronary arteries emerging from them. The right coronary artery forms the right marginal artery and the posterior interventricular artery. It gives branches to the sinoatrial node and the atrioventricular node.
The left coronary artery gives off a circumflex branch and the anterior interventricular artery. The great cardiac vein accompanies the anterior interventricular artery. The middle cardiac vein accompanies the posterior interventricular artery, and the small cardiac vein accompanies the right coronary artery, all draining into the coronary sinus, which opens into the right atrium.
Deoxygenated blood from the right atrium reaches the right ventricle, and then goes to the lungs. The oxygenated blood returns to the left atrium, then the left ventricle, which pumps blood out through the aorta, filling the aortic sinuses and back through the coronary arteries. That is coronary circulation.
To remember which veins accompany which artery, this is what I do. The great cardiac vein is great, so it likes to be upfront with the anterior interventricular artery. The middle cardiac vein is okay being in the back with the posterior interventricular artery, and the small cardiac vein is small, but it's in a big sulcus.
The coronary sulcus, along with the right coronary artery. And that is the blood supply of the heart. I hope this video was helpful.
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