06 January 2018
OXYGENATION OF THE HEART AND ITS BLOOD CIRCULATION
The heart is a muscular pump about the size of your fist, located at the centre of the thorax, between the two lungs. It is the engine of the circulatory system.
Its normal function is closely tied to its oxygenation.
The coronary arteries
Two arteries have the crucial task of supplying the heart with oxygen: these are the coronary arteries. Any reduction in the oxygen supply can have serious and sometimes irreversible consequences for the heart.
Let’s take a closer look at the coronary arteries.
Left and Right coronary
The two coronary arteries, the left and the right, are located directly on the heart. They branch out through the entire cardiac muscle.
The coronary arteries are the first to leave the aorta. Their starting point is found immediately above the aortic valve.
For those interested in a more detailed look as to how the heart circulation works, we have provided the following information
Patients who have their coronary arteries repaired through the installation of a metal stent are often curious to know the name of the repaired artery. Here, then, are a few details on the anatomy of coronary arteries.
The left coronary artery splits into two branches right after it leaves the heart. This first segment is called the left main coronary artery.
One of the branches descends along the front of the heart. This is called the left anterior descending artery. It runs along the anterior intraventricular sulcus, i.e., the groove where the heart’s two front ventricles meet.
The arteries that branch out from it are called the diagonal branches.
The circumflex artery is the second artery that stems off of the left main coronary artery. It follows the contour of the heart on the left side and the marginal arteries branch out from it.
The right coronary artery follows the contour of the heart on the right and, in nine people out of ten, descends behind the heart towards the apex. It follows the posterior groove where the right ventricle meets the left ventricle. This part of the artery is called the posterior interventricular artery.
In one person out of ten, the posterior interventricular artery is a branch of the circumflex coronary artery on the left side of the heart.
Oxygenation of the heart has differences
Blood circulation in the cardiac muscle is particular: contrary to blood circulation in the body, the blood stops flowing during a contraction.
In fact, the contraction of the cardiac muscle crushes the branches that penetrate the muscle to oxygenate it. Blood circulation is thus cut off during the contraction of the left ventricle. The blood can only pass through when the heart releases, i.e., during its resting phase.
Despite this, the heart’s oxygen requirements are met in a very effective and amply sufficient way. The human body is designed to sufficiently oxygenate this motor in charge of circulating oxygen and vital nutrients throughout the rest of the body.
In fact, even a third of the time it takes red blood cells to pass through the capillaries would be enough to deliver enough oxygen to the cardiac muscle. The capillaries are the microscopic vessels where red blood cells pass through in single file to release oxygen into the muscle and take away the carbon dioxide generated by the heart’s work.
Everything works perfectly as long as the need for oxygen is in harmony with its supply.
Four factors of consumption of "fuel"
Now let’s look at the four (4) factors that determine the heart’s oxygen (02) needs. We can compare them to the factors that affect a car’s gas consumption.
- The state of the air filter; ideally it is well-cleaned
- The car’s aerodynamics
- The power of the engine
- The speed of the car
In the heart, oxygen needs are determined by:
- The adequate filling of the left ventricle; it must be neither too empty nor too full
- The left ventricle’s resistance to emptying its contents into the aorta
- The strength of its contractions
- The heart rate
Heart medications affect these factors
In the case of certain diseases, like angina, the doctor prescribes medication to reduce the heart’s efforts and its oxygen (O2) requirements. The medication acts on one or several of these oxygen consumption factors.
It takes an oxygen carrier
As for the oxygen supply, this depends on the quantity of red blood cells present in the blood.
These are like “little boats” that are responsible for transporting oxygen in the blood.
It takes pipes
The oxygen supply also depends on the state of the piping that irrigates the heart, i.e., the coronary arteries.
These pipes are made of three layers
The coronary arteries, like all the other arteries of our body, are made of three layers.
Each one of these layers plays a specific role, but the middle one is particularly important in the development of the cholesterol plaques.
Internal layer: intima
The internal layer called intima is like a thin layer of Teflon. It is responsible for the integrity of the vessel and protects it from the formation of blood clots.
It naturally produces substances used to dilate the artery when necessary. One could compare that to the nitroglycerin that certain patients must use to relieve chest pain. The intima thus helps keep the artery at a larger size where necessary.
Middle layer: media
The media, in the center, is thicker and made up of smooth muscle cells. It gives the artery the ability to contract and to dilate.
The nitroglycerin spray that some people use for angina acts on this layer. It induces a vessel relaxation. The vessel becomes larger, circulation improves and angina is relieved.
External layer: adventitia
The adventitia is the external coating. It is the most resistant part of the artery and offers a protective effect to the vessel.
At birth, the inside of the coronary arteries is smooth and pink, but the media alters with age. It looses its suppleness, causing the arteries to harden as we grow older.
Next chapter: Angina