A Student's Guide to the Heart

When it comes to investigating how the human body functions, the heart is at the center of it all. Much like the motor of a car, it is a crucial organ that enables us to stay alive. Unlike many of our other organs, the heart works continuously without a break. Even while the body is at rest during sleep, the heart is one of the few organs that continues to work.

For all its complexity, the heart is essentially a type of pump. Just like any machine, to do its job, the heart needs to be in good condition: free of clogs and any weaknesses. It is up to each of us to take care of our heart and ensure that it is healthy. Heart disease in the U.S. is the most common cause of death, affecting around two thousand people every day! However, on the plus side, this rate has actually been slowly decreasing in recent years. Preventing heart disease is much better than trying to cure it once it occurs. Many heart conditions can only show their symptoms very suddenly. Often, by the time people try to fix it, it is already too late. It is important to understand what our hearts do and how we can help keep them as healthy as possible. In this way, we can be more aware about risks that can endanger the heart. By learning about the heart, we can educate ourselves about how to live healthier lives and avoid heart disease.

The Heart

The heart is positioned just behind the breastbone, at a point roughly between the two lungs. Most of the heart lies on the left side. To get an approximate idea of the size of your heart, have a look at how large your fist is. There are three layers that make up the heart. On the outside is the pericardium, a membrane sac that contains fluid. Beneath it is the heart’s muscular tissue called the myocardium. Finally, on the inside is a smooth membrane that lines the inner parts of the heart. It is called the endocardium.

Sounds of the Heart

If you have ever heard a normal heartbeat through someone’s chest, or through a stethoscope, you will be familiar with the rhythmic thud-thud sound. The first thud is due to the blood speeding up and slowing down. This is also the cause of the second thud, along with the vibrations of valves closing.

The Heart’s Valves and Chambers

The inside of the heart is comprised of four main areas: the right atrium (upper right), the right ventricle (lower right), the left ventricle (lower left), and the left atrium (upper left). In each of these chambers is a valve that only allows blood to flow through in one direction. When one chamber closes, the corresponding valve immediately opens, and vice versa. A single heartbeat is known as a systole. During a systole, blood is pumped out. For this to happen, the atria contract and push blood to the ventricles. Next, the ventricles contract pushing blood out. There is a brief moment of rest, called a diastole, between heartbeats. The heart’s right side works to collect blood that is low in oxygen and passes it to the lungs to be replenished. This blood then flows to the left side of the heart where it is pumped to the rest of the body.

The Cycle of Blood Flow

The flow of blood takes a long circuitous path through the heart. It starts when oxygen-starved blood flows in through veins in the heart called the inferior and superior vena cava. They lead the blood into the right atrium, down through the tricuspid valve, and into the right ventricle. Now the blood is forced through the pulmonic valve into the pulmonary artery and over to the lungs. After absorbing oxygen, the blood travels on a return route to the heart. From the lungs, it flows through the pulmonary veins, enters the left atrium, and is forced through the mitral valve into the left ventricle. Finally, it is moved through the aortic valve into the aorta and is distributed through the body.

Electricity and the Heart

The heart is an organ that works non-stop, day and night. It is powered by very small electrical charges. Certain cells are capable of producing electrical charges. They can then take the charged particles and move them into other cells, such as pacemaker cells. When these other cells receive the electrical signal, they cause the heart to contract quickly. The sinoatrial node is a pacemaker in the right atrium. The electrical impulses generated here are forced out to the two atria, making them contract. The electrical signal continues to move to the atrioventricular node in the upper right side of the heart, through to the Bundle of His, an atrioventricular bundle. The signal is now split up between bundles in the left and right areas, causing the muscles in those sections to contract. All of this is done in a fraction of a second!

If for some reason, the sinoatrial node fails, other parts of this system can kick in and take over. However, the sinoatrial node is the quickest in generating electricity. There are also additional nerves that can alter the firing rate of the pacemaker’s electrical impulses. They are contained in the autonomic nervous system.

Blood Supply and Heart Disease

In order for the heart to pump blood efficiently, it needs clear, unclogged arteries. Like the rest of the body, the heart also needs blood to keep itself going. It has a special way to do this by using the coronary arteries. They take freshly pumped blood and deliver it throughout the heart muscle. Around five percent of blood is used to power the heart. The heart has a coronary artery for each side. Each is responsible for blood supply to different sections of the heart. On the other hand, veins in the heart are used to collect blood with low amounts of oxygen from all over the heart.

Coronary artery disease is when the coronary arteries are partially or fully blocked. Often, the blockage is comprised of cholesterol that lines the artery walls. When this occurs, less blood flows to the heart and it cannot work properly. In turn, this causes chest pains because the heart has to work extremely hard to do its job. This condition is known as an angina. If the heart cannot receive any fresh blood and oxygen, its muscles can start dying. This usually occurs if the artery is fully blocked. In this case, the person would experience a heart attack.

How do people keep their hearts and coronary arteries healthy? In most cases, it’s simply a matter of healthy eating habits and getting regular physical exercise. Some people may have a genetic history of heart disease though, so it is always a good idea to have yourself tested a few times during your life.

Heart Stats

Your heart pumps around 70ml of blood each time it beats. For most average, healthy people, their hearts pump around seventy-two times every minute. If you do the math, you’ll find that the heart pumps close to two thousand gallons of blood each day! That’s what you could call hard work!

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