Coronary circulation and Venous Drainage of Heart

    

In this chapter, we are going to study the most important topic in the anatomy of the heart, i.e., the blood supply of the heart, coronary circulation. In coronary circulation, first we will understand coronary arteries.

Now, let's plan how we are going to study this topic. Firstly, we will start with the origin of coronary arteries, then their course, how they are travelling, then their branches, and at last we will study the supply of coronary arteries.

Coronary circulation

The arteries that supply blood to the heart are the coronary arteries. These arteries are two in number: the right coronary artery and the left coronary artery.

Origin of Coronary Arteries

Both the coronary arteries are going to begin from the aortic sinuses. This aortic sinus is divided into two parts, i.e., anterior and posterior aortic sinus. Now the posterior aortic sinus is further divided into right and left parts.

From the anterior aortic sinus, the right coronary artery begins, and from the left posterior aortic sinus, the left coronary artery begins. One thing to notice here, i.e., the right posterior coronary sinus does not give any coronary branch.

Now the question arises: where is this aortic sinus present? The aortic sinus is present exactly at the very beginning of the ascending aorta, thus giving three arteries, i.e., one anterior coronary artery and two right and left posterior arteries. But only two coronary arteries.Let's see in the diagram

In short, the right coronary artery starts from the anterior aortic sinus, and the left coronary sinus starts from the left posterior aortic sinus.

Now we have completed the origin; after that, we will start the course of the coronary arteries and what branches it gives.

Course and Branches of Coronary Arteries

We will study this part with a diagram:

We have studied that the right coronary artery starts from the anterior aortic sinus, which you can see in the diagram. Now this right coronary artery will go back or posteriorly and give a branch called the posterior interventricular artery, because it goes between the two ventricles and presents posteriorly. And while the right coronary artery is taking a turn, it gives a branch along the margin, known as the right marginal artery.

Now, for the left coronary artery, it originates from the left posterior coronary sinus. It is considerably shorter in length, and it gives two branches. One branch, which is going to take a turn and go back posteriorly, is called the circumflex artery. Another branch will go in between two ventricles but anteriorly, thus called the anterior interventricular artery or left anterior descending artery.

This circumflex artery gives a branch called the left marginal artery or obtuse artery, which runs along the left margin of the heart. The anterior interventricular artery also gives a branch called the diagonal branch, and it mainly supplies blood to the left ventricle.

Now let's start the difficult part, i.e.,

Blood supply

To understand this part, let's make a trick. We will cut the upper part of the heart, i.e., both atria, and make a diagram.

In this diagram you can see the right ventricle and left ventricle. Now draw an imaginary line passing through the interventricular septum diagonally.The trick is that the portion on the left side of the line is supplied by the left coronary artery, and the right side of the line is supplied by the right coronary artery.

So, the right coronary artery supplies blood to 

• Right Atrium

• Right ventricle

• Posterior part of Left Ventricle

• and posterior part of interventricular septum

Now, the left coronary artery supplies

• Left Atrium

• Left Ventricle

• Anterior part of right ventricle

• Anterior part of interventricular septum

It's not over yet; we are forgetting one thing, i.e., the nodes present inside the heart. Let's see the blood supply to the SA node and AV node.

Blood supply to the conduction system

In this diagram, you can see the conduction system of the heart without the heart. The red outlined part on this diagram is supplied by the right coronary artery and the rest by the left coronary artery.

So, the right coronary artery supplies blood to 

• SA node

• AV node

• Bundle of HIS

• Minor part of left bundle branch

The left coronary artery supplies blood to 

• Major part of left bundle branch

• and right bundle branch

I want you to remember a fact: in the case of 35 percent of the population, the SA node is supplied by the left coronary artery.

Coronary circulation 

Venous Draiange of the Heart

For venous drainage, we have the coronary sinus. The coronary sinus is present in between the atria and ventricle; there is a groove present in between the atria and ventricle, called the atrioventricular groove. So, the coronary sinus is present in the posterior atrioventricular groove.

Almost all the cardiac veins are going to drain blood into the coronary sinus, and from the coronary sinus it will go to the right atrium.

These cardiac veins will drain their blood in the coronary sinus.

• Great Cardiac Vein
• Small cardiac vein
• Middle cardiac vein

Some veins, like anterior cardiac veins, will directly drain their blood into the right atrium. 

Lets draw a simple diagram to understand:

 

We will add two more veins over there :

1. Oblique vein of left atrium (Marshall's vein)
2. Posterior vein of left ventricle

These veins also drain their blood in the coronary sinus.

Thus completing venous drainage of the heart.

Thank you for your time.