The primary role of the human heart is to force blood through vessels that lead to the lungs and all other areas of the body. This process is critical to survival because it is the mechanism by which oxygen and nutrients are delivered to tissues and waste is transported to the liver, kidneys, and intestinal tract for processing and elimination. In order for blood to flow in the proper direction, the four chambers of the heart must contract in a coordinated effort that is orchestrated using electrical signals that are generated at a rate of 60 – 100 times per minute. Diseases that damage cardiac cells and nerve fibers inside the heart have the potential to interfere with this process and may lead to severe medical problems or even death. Unfortunately, the prevalence of heart disease has increased dramatically over the past several years and it has become more important than ever for medical personnel and the public to understand cardiac employment and contracting so that they can educate others about the importance of heart health.
The standard human heart contains four chambers that work together to move blood through the body. Two small chambers known as atria are located at the top of the heart while two large chambers known as ventricles are located immediately below them. Each atrium is responsible for pushing blood into the ventricle that is located benefit it. The right ventricle forces blood into the lungs while the left ventricle forces blood out into the body. In order for blood to flow in the proper direction, the atria must contract before the ventricles. The contracting of the right and left atrium fills the ventricles with blood prior to their contracting. Valves between the atria and ventricles snap shut prior to ventricular contracting so that blood is not able to flow back into the atria. This series of contracts is accomplished through the use of electrical signals that travel from the top of the right atrium to the bottom of both ventricles.
A specialized area of tissue known as the sinoatrial (SA) node is located near the top of the right atrium and is responsible for initiating a contractile signal at a rate of 60 – 100 times per minute through life. This signal travels along a couple of nerves that lead to a second collection of tissue known as the atrioventricular (AV) node that is located near the convergence of the four chambers. As the electrical signal passes through the right and left atria, it is rapidly propagated between all of the cardiac cells using a series of cellular connections known as gap junctions. These junctions are critical for cardiac contraction because they ensure that all cells receive the signal to contract at the same time. This enables the chamber to apply maximum force to the blood so that it is moved forward in an efficient and effective manner. These junctions connect all cells in a particular chamber, but do not exist between cells that are contained in separate chambers.
Once the signal to contract has traveled through both of the atria and has arrived at the AV node, it travels along two large rivers known as the right and left bundle branches. The bundle branches carry the contractile signal through the ventricles to smaller nerves known as Purkinje fibers. These fibers are different from other nerves in the body because they are capable of transporting electrical signals at a much faster pace. Purkinje fibers carry contractile signals to individual cardiac cells where they are again propagated to all cells within the chamber through the use of gap junctions. This ensures that the ventricles contract in unison and apply maximum force to the blood contained inside.
Diseases that damage the cardiac cells and the nerve fibers can affect the ability of the heart to conduct electrical signals and contract efficiently. While there are many different diseases that can affect the heart, the most common causes of heart disease are the result of chronic diet and exercise related illnesses such as diabetes, obesity, and high blood pressure. Those who plan to work as technicians in cardiac care need to have a thorough understanding of the mechanisms of the heart so that they can provide high quality care to the patients and effectively communicate the need for heart healthy behaviors to the public.