Anatomy And Physiology

Human Heart the Main Organ of the Blood Circulatory System



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The human heart, the main organ of the blood circulatory system enclosed in pericardial sac, pumps blood to all body parts. It is the strongest muscular organ of the body and made up of cardiac muscles that work continuously without being fatigued. It comprises four parts; two upper smaller parts called atria (singular:atrium) and two lower larger parts called ventricles. The contraction of cardiac muscle tissues in ventricles causes the highest blood pressure called "Systolic pressure." Whereas the relaxation of cardiac muscle tissues in ventricles creates lowest blood pressure called "Diastolic pressure." Rhythmic heart beat is the result of the this contraction and relaxation of cardiac muscle tissues.

Blood circulation between the heart and body parts is carried out by the blood vessels. Three types of blood vessels (arteries, veins, and capillaries) carry blood to and from the heart. Arteries carry oxygenated blood from the heart to all body parts except the pulmonary artery. While veins carry de-oxygenated blood from all body parts to the heart except the pulmonary vein. The pulmonary artery carries de-oxygenated blood from the heart to the lungs while the pulmonary vein carries oxygenated blood back from the lungs to the heart. Arteries have thick walls and small lumen. But veins have thin walls with greater lumen. Therefore arteries retain their shape when blood leaves them but veins collapse. Arteries divide to form the smallest blood vessels called capillaries and capillaries combine to form veins.

A set of valves is present in the heart to keep the blood flow unidirectional. Four types of heart valves are tricuspid valve (present between right artium and right ventricle), pulmonary /pulmonic valves (present between right ventricle and pulmonary artery), mitral valve (present between left artium and left ventricle) and aortic valve (present between left ventricle and aorta, the largest artery). Each valve has a set of flaps called cusps or leaflets to open and close the valve during blood flow. Proper opening and closing of valves is responsible for proper blood flow through them otherwise it can lead to serious conditions of stroke or attack. Stenosis and regurgitation (insufficiency) are two major valve defects. In stenosis, valves cannot open properly during blood flow. While in regurgitation valves are unable to close completely after blood flow which is very important to prevent backward flow of blood. Symptoms of valve defects are dizziness, breathlessness, weakness and fainting.

An electrical conduction system is responsible for proper and efficient heart pumping. It is a complex system of electrical signals coordinating contraction and relaxation of cardiac muscle tissue for rhyhmic heart beat. Sinoatrial node (SA node-group of cells) present on the upper portion of the right atrium sends electrical impulses that trigger heart beat. These impulses struck atrioventricular (AV node) present on the lower portion of the right atrium which sends impulses to ventricles to contract. Any defect in sending electrical impulses can disrupt the rhythmic heart beat and can lead to serious conditions.

Deoxygenated blood enters the heart through superior and inferior vena cava in the right atrium which contracts to push the blood into the right ventricle through the tricuspid valve. Ventricles contract to push the blood into the pulmonary artery through the pulmonary valve. The pulmonary artery carries blood to the lungs to add oxygen to it and from here the pulmonary vein carries oxygenated blood to the left atrium. The left atrium contracts to pump the blood into the left ventricle through the mitral valve. From the left ventricle blood is pumped into the aorta through the aortic valve to supply all body parts. Each valve get closed after the blood goes through it and the next valve opens to keep a continous blood flow.

Different heart diseases can be caused by any defect of the above mentioned system. "Arrhythmias" is a heart beating disorder in which the heart becomes incapable to keep a rhythmic beating to pump the blood. It can occur even in healthy persons. About 2.2 million Americans are living with this disorder. A continuous oxygen supply is necessary for cardiac tissue which is carried out by coronary arteries. If due to any reason coronary arteries damage or blocked oxygen supply to cardiac tissues decreases causing ischemic heart disease. High cholesterol is one of the major reasons of blocking of coronary arteries, making them narrowed and less flexible through forming hard deposits on their walls. This condition is called arteriosclerosis. Clot formation completely blocks the arteries causing serious heart attack. High blood pressure is another reason for heart problems. Recent statistics show that one out of each three US adults has high blood pressure. But due to no obvious symptoms many people are unaware of having it. Therefore it is also called the "Silent killer" and if not controlled it can also cause heart stroke or attack. Congenital (inborn) heart diseases in which heart or blood vessels do not develop normaly before birth can be treated after birth through proper medication.

Despite all of the above complexities and heart defects, low cholesterol food, daily exercise, no smoking, and proper doctor advice can enable a person to prevent all heart defects and to have a complete, healthy, and normal life

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