HOW THE HEART WORKS
PART II
THE LONGEST LIST OF THE LONGEST STUFF AT THE LONGEST DOMAIN NAME AT LONG LAST

How does the heart work?

This blood then goes to the lungs and fills itself with oxygen. It then travels through the pulmonary veins back to the heart and enters the left atrium. As the left atrium contracts, blood is pushed through the mitral valve and travels into the left ventricle. Although all ventricles of the heart are important, the left ventricle is the most important. This is because it takes the blood that it receives and pushes it through the aorta, which is the main artery in the body. This delivers the oxygen-rich blood back to the different parts of the body. The left ventricle is the thickest part of the heart due to the amount of muscle that it takes to push the blood throughout the body against a much higher pressure in circulation.

The contracting and relaxing of the heart is due to the hearts electrical system. The electrical system is comprised of a group of cells that have the ability to create electrical activity on their own. This group of cells pull charged particles apart and pushes them throughout the cells. This causes an electrical current in the pacemaker cells and those cells distribute themselves among the heart and that causes the heart to contract. The pacemaker cells do this at a remarkable speed, every second of the day. It is these impulses that cause the heart to contract.

The sinoatrial node is the term for the pacemaker in the heart. This node is located in the right atrium. There are fibers within the heart that take the electricity from the pacemaker and distribute it throughout the rest of the heart. It takes a total of 0.4 seconds for the electricity to leave the sinoatrial node and go to the left and right atria, making them contract. The electricity then travels to the atrioventricular node and to the Bundle of His. It then separates into two different branches: the right bundle branch and the left bundle branch. From there, it moves quickly to the Purkinje fibers in the right and left ventricles, causing them to contract at the same time.

Although any of the electrical components of the heart have the ability to be the pacemaker, the sinoatrial node moves at a much faster rate. If the sinoatrial node were to ever break down, another electrical component could replace it as the pacemaker but the entire process would happen more slowly. The pacemaker is responsible for producing the electrical currents that cause the heart to beat, there are nerves that can affect how the pacemaker does so. These nerves make up the autonomic nervous system, which is comprised of two parts: the sympathetic nerves, which quicken the heart rate and increase the strength of the contraction, and the parasympathetic nerves, which slow down the heart rate and decrease the strength of the contraction.

The arteries in the heart need to be kept clean so that a heart attack does not result. The two main coronary arteries are the left main coronary artery and the right coronary artery. The left main coronary artery branches out into the left anterior descending branch and the left circumflex arteries. Each of these arteries takes blood to the different parts of the heart and the electrical system.

When one of these coronary arteries becomes blocked, that artery cannot deliver blood to the heart that the heart needs to perform properly. This is why when someone has heart disease, high activity levels and exertion will cause them to tire quickly and feel chest pain. Once the artery has some blockage, this is called angina and if the blockage becomes worse, it’s called unstable angina. Once the artery is completely blocked, a heart attack will occur.

The Heart

PART I

 

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