The human heart is one of the most fascinating structures found within the human body. It serves as an extremely efficient pump, which never rests, never stops, and tirelessly pumps blood around your body every minute of every day for your entire life.
The basic structure of the heart involves four major chambers. The two smaller chambers on the top of the heart are known as the atria, both left and right respectively. Along the bottom of the heart are the two larger, more muscular chambers known as the ventricles. Again both left and right. The heart is almost entirely made of a specific type of muscle known as cardiac muscle. This type of muscle is different that muscle found along your bones which you can actively control. The differences are somewhat subtle, but significant. One of the more practical consequences of these differences is that your heart muscle does not get tired in the same way your skeletal muscle does. And that's a good thing.
Separating each of the four chambers are a series of valves, which keep the blood flowing in one direction. This is important as you do not want blood to back up into the chamber from which it came. Proper blood flow requires that the blood move along from one chamber to the next in the proper order, which I'll detail further down this article.
The heart is controlled by a complex system of electrical signals. These signals originate in a small cluster of cells on the surface of the right atria known as the Sinoatrial Node, and travel through the heart stimulating the cardiac muscle tissue in just the right way to cause the pump to function properly. Disruptions in this electrical flow are the cause of many heart problems and arrhythmias.
Despite the massive amount of blood that flows through the heart in any given minute, the tissue of the heart itself is not capable of using the oxygen from the blood that it is pumping. Because of this there is an entire system of arteries, known as the coronary arteries, which feed oxygen to the tissues of the heart directly. It is damage to the coronary arteries that is responsible for much heart disease. When they become blocked, which is common in certain medical conditions due to their small size and vulnerability, the tissues of the heart are no longer supplied with the proper amount of oxygen, and will stop beating. Needless to say, this is not a good thing.
BLOOD FLOW TO THE HEART
Blood begins its journey through the heart in the right atria. There are two separate and very large veins which dump blood directly into the atria. These are known as the superior vena cava and the inferior vena cava. When the right atria is filled and the cardiac cycle reaches a point where it is time to empty it out, the right atria contracts, pushing the blood through the tricuspid valve, which leads to the right ventricle.
The right ventricle is slightly larger and more muscular chamber than the right atria as its function is to push the blood all the way into the lungs. When the right ventricle is full and the cardiac cycle reaches a point where it is necessary to move the blood out of the right ventricle, the ventricle contracts. The tricuspid valve closes, preventing the blood from returning to the right atria and the blood is pushed out of another valve, known as the pulmonary valve and into the pulmonary artery. The pulmonary artery leads directly to the lungs.
The blood then picks up oxygen in the lungs and begins his journey back to the heart via the pulmonary veins.
The oxygenated blood from the pulmonary veins enters the left atria. When the left atria contracts, the blood is pushed through the mitral valve, which is the valve connecting the left atria to the left ventricle. The left ventricle is the largest and strongest of the four chambers of the heart. This is because it is responsible for pushing the blood out of the heart and distributing it throughout the rest of the body. When the left ventricle begins contracting the mitral valve closes, which prevents the blood from flowing backwards into the left atria. At the same time, the aortic valve, which is the valve leading out to the major artery of the body known as the aorta, opens and allows the blood to leave the heart.
Needless to say, the timing and coordination required by the heart to make all of these things happened simultaneously is quite complex. There are numerous chances for things to go wrong during the cardiac cycle. If any of the valves become incompetent and allowing blood to flow backwards, you have what is known as regurgitation. Regurgitation of the mitral valve is one of the most common murmurs heard by cardiologists. The valves can also become stiffened and not open properly. This condition is called stenosis and can lead to heart failure in advanced cases.
If the electrical signaling that causes the cardiac tissue to contract properly gets disrupted, the timing of the contractions will also be disrupted. This can lead to numerous types of arrhythmias, which is just a fancy way of saying that the rhythm is not proper. Arrhythmias can be harmless or extremely serious and deadly, depending on the particular type and severity of the arrhythmia.
As mentioned before, the coronary arteries play a vital role in the proper functioning of the heart as well. These arteries are responsible for bringing oxygen to the tissues of the heart directly. If this flow of oxygen is disrupted for any reason, the tissues of the heart, which have a very high demand for oxygen because they never stop eating, will die off rather rapidly. In medical terms, this is known as ischemic heart disease. In more common terms you may know this as a heart attack.
In literature and poetry the human heart is often portrayed as the center of the human soul. In medicine the human heart is no less important. Without the heart beating in rhythm, you can measure your life in seconds. When it's functioning well, it can supply you body with the vital blood supply needed to support life for decades without stopping.