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Ammar
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العمر : 30
عدد الرسائل : 753
البلد : مصر أم الدنيا
العمل/الترفيه : طالب
الجامعة : حلوان
الكلية : العلوم
الشعبة : biomedical physics
تاريخ التسجيل : 25/11/2007
نقاط : 23673
http://biophysics.3oloum.org

How our Heart Works

في الأربعاء أغسطس 20, 2008 6:03 pm
About a hundred times a minute, 100,000 times a day, 36.5 million times a year, your heart keeps the beat... the beat of life. That familiar thump, thump, thump tells you that your heart is doing its job pumping blood from the veins to the heart and lungs, where it is replenished with oxygen and then distributed back to the body through the arteries. How does the heart work? Read on.

The human heart is really a pump, a powerful muscle the size of your fist that circulates blood to and from the body's millions of cells. It's divided into four chambers. There are two chambers on each side with a wall-like divider between them called a septum that separates the left side from the right side. These two receiving chambers have two passageways called valves. Each side of the heart has two valves that allow blood to pass through the heart. The tricuspid valve on the right and the mitral valve on the left regulate blood flow between the atrium and the ventricle on each side. The right valve is called the pulmonary valve and it allows blood to flow from the right ventricle to the pulmonary arteries, which supply the lungs. The left valve is called the aortic valve, which regulates blood flow from the left ventricle to the aorta.



In the normal adult, the heart pumps five liters of blood, which is recirculated continuously through the body. The blood moves from the heart into tubes called arteries, then into tiny tubes called capillaries and finally into the veins that lead back to the heart.

The entire cycle takes about 60 seconds, during which the blood brings nourishment and oxygen to all the body's cells in the tissues, organs, muscles and bones.

Here's a more complex description of the blood's journey through the body: The blood moves from the left atrium to the left ventricle through the mitral valve. As the left ventricle contracts, it pushes open the aortic valve and the blood is carried into the aorta, which distributes it to all other body organs including the heart by way of the coronary arteries. These arteries wind around the heart to keep the heart muscle supplied with oxygen and nutrients for its continuous pumping job.

As wastes are produced, they are delivered through the blood to the right atrium through the vena cava. The accumulated blood pushes open the tricuspid valve, allowing the blood to pass from the right atrium to the right ventricle. After the chamber fills, the heart contracts and the pulmonary valve opens. Blood then flows from the right ventricle into the pulmonary artery.

The pulmonary artery, which has two branches, carries blood to the right and left lungs. From the lungs, the capillary vessels carry the blood along the lungs' tiny air sacs. As the lungs breathe, carbon dioxide is passed from the body and oxygen is taken in. As this transfer occurs, the blood changes from purple or dark red to bright red.

After passing through the lungs, the blood is brought by the pulmonary veins into the left atrium. From there, the blood starts its course through the left ventricle and aorta again.


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رقصت علي جثـــث الأســود كـــلاب
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الاســــــودإسود والكـــلاب كـــلاب
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