Anatomy And Physiology

This is how the Heart Works



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"This is how the Heart Works"
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The human heart is a living machine that works as a pump in distributing blood that transports oxygen and nutrients to cells throughout the body. The heart is a mechanical marvel in that it never rests. Even when sleeping, a human being's heart is beating approximately sixty times a minute; 3,600 times an hour; 86,000 times in one day, and nearly thirty million times in one year! Each heart beat results in the pumping of sixty to seventy cubic centimeters of blood, or over 200,000 quarts of blood each year. It is the unique properties of the human heart heart that enables it to perform its job this efficiently and effectively.

First of all, the heart is composed of specialized muscle, called cardiac muscle. Its fibers form branches, instead of elongated bundles as the muscles in our arms and legs. The heart is a small organ; around the size of a man's fist. The individual muscle cells of the heart are also unique in that they automatically contract in a rhythmical fashion. This rhythm is controlled by a portion of the heart that is known as the sinoatrial node, or SA node, which functions as the pacemaker of the heart. It emits a regular electrical impulse that stimulates all cardiac muscle cells to contract, then relax simultaneously. This electrical activity can be analyzed by a diagnostic test called an electrocardiogram, or ECG. An abnormal ECG recording indicates a disruption in the transmission of the electrical impulses from the SA node to the heart muscle, which may result in impaired cardiac function.

Second, the heart is made up of four separate chambers. Two smaller chambers, called atria, are located at the top, while the two larger chambers, called ventricles, make up the lower section. The ventricles have thicker walls of muscle than the atria, and serve as the actual pumping mechanism. The left ventricle is larger than the right, and pumps blood throughout the body, which is known as systemic circulation. The right ventricle pumps blood to the lungs, where the blood releases carbon dioxide to the lung, then picks up oxygen from the lungs after it is inhaled. The carbon dioxide is eliminated from our bodies every time we exhale. This oxygenated blood is then returned to the heart's left atrium, where it flows through the mitral valve to the left ventricle. The mitral valve on the left side of the heart, and the tricuspid valve on the right side of the heart are responsible for maintaining blood flow in one direction, in order to maximize the heart's pumping efficiency.

Human behavior is the primary factor in causing heart disease, which is represented by poor diet, lack of exercise, smoking tobacco, or ingesting drugs as cocaine and amphetamines (both increase heart rate). A lifestyle that creates elevated levels of prolonged stress is another risk factor for heart disease. According to the American Heart Association, elevated levels of blood cholesterol from high fat diets, cigarette smoking, and prolonged stress lead to coronary heart disease. The coronary arteries, which supply oxygen and nutrients to the heart muscle, accumulate fatty desposits until they become narrowed or even completely blocked. This results in chest pain, called angina, and may ultimately result in a heart attack, in which the heart muscle actually dies.

As with any machine, poor maintenance will result in diminished performance. The heart is a machine, but unlike an automobile engine, it is expected to run for many, many years. A healthy lifestyle is essential for the human heart to function at its optimal level.

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