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The heart
weighs between 7 and 15 ounces (200 to 425 grams) and is a
little larger than the size of the average fist. By the end of a
long life, a person's heart may have beat (expanded and
contracted) more than 3.5 billion times. In fact, each day, the
average heart beats 100,000 times, pumping almost 2,000 gallons
(7,571 liters) of blood.
The heart is
located between the lungs in the middle of the chest, behind and
slightly to the left of the breastbone (sternum). A
double-layered membrane called the pericardium surrounds the
heart like a sac. The outer layer of the pericardium surrounds
the roots of the heart's major blood vessels and is attached by
ligaments to the spinal column, diaphragm, and other parts of
the body. The inner layer of the pericardium is attached to the
heart muscle. A coating of fluid separates the two layers of
membrane, allowing the heart move as it beats, yet still be
attached to the body.
The heart has
four chambers. These chambers prevent oxygenated and
deoxygenated blood from mixing. The upper chambers are called
the left and right atria, and the lower chambers are called the
left and right ventricles. A wall of muscle called the septum
separates the left and right atria and the left and right
ventricles. The left ventricle is the largest and strongest
chamber in the heart.
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Diagram of the heart and various labeled structures |
Cross-Section of the heart with interior structures
labeled with the basic blood flow path. |
The function
of the heart is to pump oxygen rich blood to each and every cell
of the body.
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Blood flows from the body into the right atrium of the
heart. The blood in the right side of the heart has been
used by the body and has little oxygen left in it (is
deoxygenated or oxygen-poor). |
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The oxygen-poor blood
flows from the right atrium through the tricuspid valve
into the right ventricle of the heart. |
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From the right ventricle, blood is pumped through the
pulmonary valve into the blood vessel that goes to the
lungs. In the lungs, this blood undergoes oxygenation
process. |
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Oxygen-rich blood flows from the lungs through the blood
vessels back into the heart's left atrium. |
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From
the left atrium, blood goes through the mitral valve and
into the left ventricle. |
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The
left ventricle pumps blood through the aortic valve to a
major blood vessel called the aorta and out into the body. |
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The blood delivers oxygen to the body,
then returns through veins to the right atrium and
repeats the blood flow cycle. |
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The
Blood Cycle |
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