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The Heart and Circulation
Heart never comes into rest condition while it transfers blood to the rest of the body system; it actually works harder in comparison to any other muscle in the body system and requires a much higher blood supply than other muscles. The heart gets blood for itself through two coronary arteries, the right and the left arteries, which leave the aorta about half inch above the aortic valve and run around outside of the heart. Both arteries lie in grooves at the outside of the heart muscle and branch off into a system of smaller vessels and capillaries which supplies the muscle fibers. After delivering off its oxygen in the capillaries, the blood passes through coronary veins and drains directly into the right atrium, where it joins the venous blood from the rest of the body. When the heart works harder than usual, the coronary arteries increases oxygen supply for the heart muscles. During the extreme physical stress, flow in these arteries may increase up to five to six times. When blood supply does not meet the increased requirements in oxygen and nutrients and to wash away wastage materials, the heart aches occurs, just as other muscles might ache from an excessive workload. The lack of oxygen causes nerve cells, and chest pain, or angina pectoris. In comparison to other muscles of the body, however, the heart cannot stop for rest without devastating consequences.
Electrical current which regulates the heart activity starts in heart cells and extend through a specialized network of fibers known as the heart’s conduction system. Major elements of heart conduction system include the senatorial node or sinus, the atrioventricular node. The sinus node, called as the heart’s pacemaker, is a microscopic bundle of specialized cells that are located in the top right corner of the heart. Any portion of the heart muscle is capable of generating of electrical impulses, but in normal function, the impulses originate in this acemaker.
If the pacemaker’s functionality is interrupted, another part of the conduction system can take the charge over the impulse-firing task. Impulses are always transmitted through muscle fibers of the two atria to the atrioventricular node, located on the juncture between the right and left sides of the heart, in the area where the right atrium and right ventricle comes closer.
Electrical activity which coordinates the rhythmic contraction and relaxation of the heart’s chambers are known as the cardiac cycle. Most of the currents in the heart are lesser than a millionth of an ampere but they exert a great influence on the heart muscle. The cardiac cycle is made up of two phases, known as diastole and systole. Diastole is a phase during which the heart’s ventricles are relaxed, is the longer phase, which takes up approximately two-thirds of the cycle. Systole is the second phase during which blood is ejected from the ventricles, takes up the remaining one third. During the diastole phase, the sinus node generates an impulse that forces the two atria to contract. In diastole phase, the tricuspid and mitral valves are always open, and blood is forced to flow from the atria into the relaxed ventricles. By the end of diastole phase, the electric impulse reaches to ventricles, causing them to contract. During systole phase, the contracting ventricle closes the tricuspid and mitral valves. Just after to that, the pressure of the blood inside the ventricles raises enough to force the pulmonary and aortic valves to open, and blood is transformed into the pulmonary artery and the aorta. When the ventricles relax again, blood backs up from the pulmonary artery and the aorta and closes the pulmonary and aortic valves. The pressure in the relaxed ventricles becomes lower than in the atria, the tricuspid and mitral valves open again, and the cardiac cycle starts a new process. This seems to be a long sequence of events but it is completed approximately in a second. The familiar double throb of the beating heart is a result of the two sets of synchronized contractions which occurs during the process of cardiac cycle: The throbbing sound that we hear comes not only from the snapping of the valves, but also from the accompanying vibrations of other heart structures and from the turbulence produced by the flow of blood.
About the Author:
Prashant Jain
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Article Source: ArticlesBase.com – The Heart and Circulation
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