What the Heart Does

The heart is a muscular organ located in the left center part of the chest between the lungs. It is about the size of your fist. Its purpose is to pump blood to all the tissues in the body through a network of blood vessels. The right side of the heart pumps blood through the lungs where it picks up oxygen. The left side of the heart receives the blood containing oxygen and pumps it to the rest of the body.

Inside Your Heart

Chambers and Valves of the Heart :
The heart contains four chambers or compartments. The heart pumps blood by contracting (squeezing blood out of its chambers) and relaxing (allowing blood to enter its chambers). The two upper chambers are referred to as the atria. They receive blood returning from the body through veins. The two lower chambers are referred to as the ventricles. They are the chambers where blood is pumped into the body through arteries. The two atria mildly contract to push blood into the ventricles. The ventricles contract forcefully in order to propel blood to the lungs and the rest of the body. The chambers on the left side of the heart must generate higher pressures (work harder) in order to push blood and fluids through the body. Therefore the left side of the heart is more muscular than the right.

The heart has four major valves. Their purpose is to allow blood to flow in only one direction. The mitral and tricuspid valves control the flow of blood from the atria to the ventricles. The aortic and pulmonary valves control the flow of blood out of the ventricles.

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Circulation :
The purpose of blood is to carry oxygen and other nutrients to tissues and organs in the body and to carry away waste products. There are actually two loops of circulation in the body. The first is a circulation loop which goes from the heart to the lungs where blood is mixed with oxygen and carbon dioxide in the blood is released. The purpose of oxygen in the blood is to give the body energy. Carbon dioxide is waste that the body makes when it uses oxygen. The other circulation loop goes to the body where oxygen and other nutrients are exchanged for carbon dioxide and waste products. Veins are the blood vessels which return blood to the heart. Arteries are the blood vessels which carry blood away from the heart to the rest of the body.

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The Heart Muscle and Cardiac Cycle

The fibrous muscle of the heart (the myocardium) is important because it produces the forces needed to push blood from the ventricles. When the ventricles contract, they force blood out through valves and into the aorta or pulmonary artery. This phase of the heart cycle is referred to as systole. When the ventricles relax, blood flows into them from the atria. This phase is called diastole. See Figure 1-3.

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Problems with the heart’s myocardium can lead to heart failure. If the myocardium does not receive enough blood (and thus oxygen) due to a narrowing or blockage of the coronary arteries, a myocardial infarction (heart attack) can occur. There are various other diseases that can cause the heart muscle to weaken. If this occurs, a heart chamber can become thickened or the heart itself can become enlarged and cannot work normally. This thickening of the heart muscle is called hypertrophy and can slow down the flow of blood

The Conduction System

The conduction system of the heart consists of specialized nerve tissue that generate electrical impulses and trigger the heart to contract. The conduction system is important because it regulates heart rate (the number of beats per minute) and ensures that the heart chambers contract in an organized way. The normal resting heart rate for an adult is 60 -100 beats per minute. Problems with the heart’s conduction system can result in fibrillation (rapid and uncoordinated beating of the chambers) and can lead to additional heart problems or failure. A person in sinus rhythm has a heart that contracts in a normal, coordinated manner.

Normal, Healthy Heart Valves

Human heart valves are remarkable structures of the heart’s anatomy. These tissue-paper thin membranes attached to the heart wall undergo a constant “beating” (a flexing of the tissue) day after day, year after year. In fact, they withstand about 80 million beats a year, or 5 to 6 billion beats in an average lifetime. Each beat is an amazing display of strength and flexibility.

Structure and Location

Heart valves are structures that only allow blood to flow one way in the circulatory system. The valves are strong, thin leaflets of tissue anchored to an opening that attaches to the myocardium. There are four cardiac valves. Two of the valves are referred to as the atrioventricular (AV) valves. They control blood flow from the atria to the ventricles and prevent blood from flowing back. The AV valve on the right side of the heart is called the tricuspid valve. The name tricuspid refers to the three flaps making up the valve. The AV valve on the left side of the heart is called the mitral valve. It is sometimes also called the bicuspid valve because it has two flaps.

The other two cardiac valves, the aortic and pulmonary valves, are outflow valves and are also referred to as the semilunar valves because their three flaps are shaped like half moons. They control blood flow out of the ventricles. The aortic valve is located at the top of the left ventricle (between the left ventricle and the ascending, or upper portion of the aorta). The pulmonic valve is located between the right ventricle and pulmonary artery. The mitral and tricuspid valves are substantially larger than the aortic and pulmonary valves.

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The characteristic heart sounds (“lubb, dubb”) are caused by the closing of the heart valves, the first by closure of the mitral and tricuspid valves and the second by the closure of the aortic and pulmonary valves.

Function of Heart Valves

A perfect valve would be one which minimizes any obstruction and allows blood to flow freely in one direction. It would close completely and quickly not allowing any blood to flow back through the valve (regurgitation). Closure regurgitation is backflow through a valve as the leaflets close, leakage regurgitation is backflow through the leaflets when they are closed. In normal functioning valves there should be no leakage regurgitation. The orifice-annulus ratio is the ratio of the valve opening area to the valve annulus diameter. In an ideal valve this ratio should be 1:1.

When a heart valve opens fully and evenly, blood flows through the valve in a smooth and even manner. When a valve does not open fully or evenly, blood flowing through it can become turbulent and have areas of pooling. This type of blood flow can result in blood clots forming. Blood, rather than flowing forward, flows backwards through the valve (regurgitation) or in circles. This condition causes the heart to work harder to pump the same amount of blood. Regurgitation can also occur when a heart valve does not close quickly or completely.