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| How does the heart beat? | |
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| Topic Started: May 23 2008, 07:10 PM (39 Views) | |
| jamali | May 23 2008, 07:10 PM Post #1 |
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 How does the heart beat? An electrical stimulus is generated by the sinus node (also called the sinoatrial node, or SA node), which is a small area of specialized tissue located in the right atrium (right upper chamber) of the heart. Under normal conditions, the sinus node generates an electrical stimulus every time the heart beats (60 to 190 times per minute, depending on the age of the child and his/her activity level). This electrical stimulus travels down through the conduction pathways (similar to the way electricity flows through power lines from the power plant to your house) and causes the heart's lower chambers to contract and pump out blood. The right and left atria (the two upper chambers of the heart) are stimulated first and contract a short period of time before the right and left ventricles (the two lower chambers of the heart). The electrical impulse then travels from the sinus node to the atrioventricular (AV) node, where impulses are slowed down for a very short period, and continues down the conduction pathway via the bundle of His into the ventricles. The bundle of His divides into right and left pathways to provide electrical stimulation to both ventricles. Normally, the electrical impulse moves through the heart's conduction system, the heart contracts at about 60 to 190 times a minute (again depending on the age and activity level of the child). Each contraction of the atria and the ventricles represents one heartbeat. The atria contract a fraction of a second before the ventricles so the blood empties into the ventricles before the ventricles contract. Under some conditions, almost all heart tissue is capable of starting a heartbeat, or becoming the "pacemaker," just like the sinus node. An arrhythmia (abnormal heartbeat) may occur when: * the heart's natural pacemaker (the sinus node) develops an abnormal rate or rhythm. * the normal conduction pathway is interrupted. * another part of the heart takes over as pacemaker. Topic Home Page | Return to Full List of Topics The information on this Web page is provided for educational purposes. You understand and agree that this information is not intended to be, and should not be used as, a substitute for medical treatment by a health care professional. You agree that Lucile Salter Packard Children’s Hospital is not making a diagnosis of your condition or a recommendation about the course of treatment for your particular circumstances through the use of this Web page. You agree to be solely responsible for your use of this Web page and the information contained on this page. Lucile Salter Packard Children’s Hospital, its officers, directors, employees, agents, and information providers shall not be liable for any damages you may suffer or cause through your use of this page even if advised of the possibility of such damages. |
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| jamali | May 23 2008, 07:14 PM Post #2 |
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It's small, a little larger than a clenched fist. Relatively simple in function, your heart's primary purpose is to pump...24 hours a day, 70 to 80 times a minute. With each beat, the heart pumps blood that delivers life-sustaining oxygen and nutrients to 300 trillion cells. Each day the average heart "beats" (or expands and contracts) 100,000 times and pumps about 2,000 gallons of blood. In a 70-year lifetime, an average human heart beats more than 2.5 billion times, pumping approximately 1 million barrels of blood.  The circulatory system is a network of flexible tubes through which blood flows as it carries oxygen and nutrients to all parts of the body. It includes the heart, lungs, arteries, arterioles (small arteries) and capillaries (minute blood vessels). It also includes venules (small veins) and veins, the blood vessels through which blood flows as it returns to the heart. If all these vessels were laid end-to-end, they would extend for about 60,000 miles--far enough to encircle the earth more than twice. To learn more about how the heart accomplishes all this, you might want to explore the following web sites. |
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| jamali | May 23 2008, 07:17 PM Post #3 |
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Map of the Human Heart Let's get straight to the heart of the matter--the heart's job is to move blood. Day and night, the muscles of your heart contract and relax to pump blood throughout your body. When blood returns to the heart, it follows a complicated pathway. If you were in the bloodstream, you would follow the steps below one by one.  Oxygen-poor blood (shown in blue) flows from the body into the right atrium. #2 Blood flows through the right atrium into the right ventricle. #3 The right ventricle pumps the blood to the lungs, where the blood releases waste gases and picks up oxygen. #4 The newly oxygen-rich blood (shown in red) returns to the heart and enters the left atrium. #5 Blood flows through the left atrium into the left ventricle. #6The left ventricle pumps the oxygen-rich blood to all parts of the body.  Do right and left seem backward? That's because you're looking at an illustration of somebody else's heart. To think about how your own heart works, imagine wearing this illustration on your chest. Did you know that your heart beats over 100,000 times a day? Get "heart smart" by checking out these |
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| waqarabro | May 23 2008, 08:22 PM Post #4 |
Swash-buckling
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 informative |
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| jamali | May 24 2008, 09:24 AM Post #5 |
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