Coronary circulation

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Introduction0:00–0:56

## IntroductionWith coronary circulation, coronary comes from the Latin word “coronarius,” meaning "crown." This is because the coronary blood vessels surrounding the heart resembles a little crown!
And circulation refers to “the flow of blood.” So, coronary circulation is the movement of blood throughout the vessels that supply the myocardium also known as the heart muscle.
Now, the heart is a pump, primarily made up of cardiac muscle cells known as cardiomyocytes. And like any other cell, they require a steady supply of oxygen, nutrients, and a way to eliminate wastes.
And although the heart is continually pumping blood throughout its chambers, the myocardium is too thick for the diffusion of blood to happen effectively.
So, instead, the coronary circulation provides an efficient way for the exchange of substances to occur. ## Coronary circulationOkay, the coronary circulation system is mainly made up of arteries and veins.

Coronary Circulation0:56–1:16

To begin, the arterial supply of the heart starts with the branching out of the left and right coronary arteries from the base of the aorta.
It’s like a superhighway that carries oxygenated blood from the heart to the rest of the body.## Left Coronary ArteryNow, the left coronary artery heads along the left coronary sulcus, a groove on the outer surface of the heart that marks the point of division between the ventricles and the atria.

Left Coronary Artery1:16–2:15

Not too far along the sulcus, the left coronary artery divides into two major branches. The first is the left anterior descending artery or LAD.
It travels down the anterior interventricular sulcus, and it supplies the anterior 2/3 of the interventricular septum, the anterolateral papillary muscle, and the anterior surface of the left ventricle.
The second branch is the left circumflex artery or LCX. It goes along the coronary sulcus, around the left side of the heart and supplies the left atrium and the posterior walls of the left ventricle.

Right Coronary Artery2:15–3:19

## Right Coronary ArteryAlternatively, the right coronary artery heads in the opposite direction, following the coronary sulcus, and along the way it supplies the SA node It later divides into two branches.
The first is the right marginal artery, which stretches along the margins of the bottom right side of the heart, supplying the right ventricle.
The second branch is the posterior descending artery or PDA, sometimes called the posterior interventricular artery. It goes down the posterior interventricular sulcus towards the heart’s apex while supplying the posterior 1/3 of the interventricular septum the posterior 2/3 of the ventricular walls, and the posteromedial papillary muscle.
At the apex, the posterior descending artery merges with its anterior counterpart, through interconnected arterial branches called anastomoses.
Together, they supply the right atrium and nearly all of the right ventricle. ## Anatomical VariationsNow, the anatomical layout of the coronary arteries can vary considerably.

Anatomical Variations3:19–4:12

The most common variation is the origin of the posterior descending artery, as it can branch off from either the right or left coronary artery, sometimes even both!
So, if the posterior descending artery is supplied by the right coronary artery, then it's described as a right-dominant circulation.
And it's the most common. If it arises from the left circumflex, it's a left-dominant circulation, which is not so common.
And if it arises from both the right coronary and left circumflex artery, it's known as a codominant circulation, and it's way rarer than the others.
There are even more and stranger variations, like there being a left marginal artery and right marginal artery. ## Epicardial VesselsNow, the coronary arteries and their main branches lie in the epicardium, or the outer layer of the heart wall, and they send branches inward to supply the myocardium.

Epicardial Vessels4:12–4:46

So, when the ventricles contract during systole, they compress the coronary circulation which causes a brief period of occlusion and reduced blood flow.
On the other hand, when the ventricles relax, or diastole, the compression upon the coronary circulation is relieved and blood flows readily.
## Cardiac VeinsThe coronary circulation is also made up of veins, called cardiac veins. They are responsible for returning deoxygenated blood and waste products like carbon dioxide, from the myocardium to the lungs.

Cardiac Veins4:46–6:01

The blood moves from the capillary beds of the myocardium into the cardiac veins. The cardiac veins usually follow the same path as the coronary arteries.
So, just like their arterial counterparts, there’s the great cardiac vein in the anterior interventricular sulcus, a middle cardiac vein in the posterior interventricular sulcus, and a small cardiac vein, running along the inferior margin of the right heart.
All three cardiac veins empty into one big vessel behind the heart called the coronary sinus which empties into the right atrium.
Then there's also the anterior cardiac veins, which generally empty directly into the right atrium bypassing the coronary sinus.
The blood then gets pumped from the right atrium to the right ventricle, through the pulmonary trunk and finally the lungs where the red blood cells can pick up oxygen and dump off carbon dioxide.
## Blood FlowNow, blood flow through the coronary circulation is controlled primarily by local metabolic factors like adenosine and oxygen availability, with sympathetic innervation involved in the 'fight or flight' response, playing a minor role.

Blood Flow6:01–6:56

. So, let’s say a scientist was running away from a zombie raccoon.
Naturally, the fight or flight response kicks in and her myocardium would contract more forcibly. causing it to consume more oxygen, thereby decreasing local oxygen molecules also known as hypoxia.
In response to the local hypoxia, the coronary arterioles vasodilate. In effect, making more space for blood to flow, which increases oxygen delivery to meet the demands of the panicking heart.
So, when there’s an increase in blood flow to the myocardium due to an increase in metabolic activity, it’s called active hyperemia.
## ReviewAlright, as a quick recap, the coronary circulation is the blood that circulates throughout the coronary vessels that supply the myocardium.

Summary6:56–7:58

The coronary arterial circulation starts at the base of the aorta with the left and right coronary artery. The left coronary artery generally gives off the circumflex artery and the left anterior descending artery.
The right coronary artery gives off the marginal artery and the posterior descending artery. Now, the cardiac veins are mainly made up of the great cardiac vein, middle cardiac vein, and the small cardiac vein which drain into the coronary sinus and ultimately into the right atrium.
Blood flow through the coronary circulation is primarily controlled by local metabolic factors like adenosine and oxygen availability, with sympathetic innervation, playing a minor role.