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Anatomy of the Human Heart
(En español)
Click here for a Flash version of this illustration of anatomy of the heart.
The Heart
The
heart weighs between 7 and 15 ounces (200 to 425 grams) and is a little
larger than the size of your 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 about 2,000 gallons (7,571 liters) of blood.
Your
heart is located between your lungs in the middle of your chest, behind
and slightly to the left of your breastbone (sternum). A double-layered
membrane called the pericardium surrounds your heart like a sac. The
outer layer of the pericardium surrounds the roots of your heart's
major blood vessels and is attached by ligaments to your spinal column,
diaphragm, and other parts of your body. The inner layer of the
pericardium is attached to the heart muscle. A coating of fluid
separates the two layers of membrane, letting the heart move as it
beats, yet still be attached to your body.
Your
heart has 4 chambers. 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 your heart. The left ventricle's chamber walls
are only about a half-inch thick, but they have enough force to push
blood through the aortic valve and into your body.
The Heart Valves (illustration)
Four types of valves regulate blood flow through your heart:
- The tricuspid valve regulates blood flow between the right atrium and right ventricle.
- The pulmonary valve controls blood flow from the right ventricle into the
pulmonary arteries, which carry blood to your lungs to pick up oxygen.
- The mitral valve lets oxygen-rich blood from your lungs pass from the left atrium into the left ventricle.
- The
aortic valve opens the way for oxygen-rich blood to pass from the left
ventricle into the aorta, your body's largest artery, where it is
delivered to the rest of your body.
See also on this site: The Heartbeat
The Conduction System (illustration)
Electrical
impulses from your heart muscle (the myocardium) cause your heart to
contract. This electrical signal begins in the sinoatrial (SA) node,
located at the top of the right atrium. The SA node is sometimes called
the heart's "natural pacemaker." An electrical impulse from this
natural pacemaker travels through the muscle fibers of the atria and
ventricles, causing them to contract. Although the SA node sends
electrical impulses at a certain rate, your heart rate may still change
depending on physical demands, stress, or hormonal factors.
The Circulatory System (illustration)
Your
heart and circulatory system make up your cardiovascular system. Your
heart works as a pump that pushes blood to the organs, tissues, and
cells of your body. Blood delivers oxygen and nutrients to every cell
and removes the carbon dioxide and waste products made by those cells.
Blood is carried from your heart to the rest of your body through a
complex network of arteries, arterioles, and capillaries. Blood is
returned to your heart through venules and veins. If all the vessels of
this network in your body were laid end-to-end, they would extend for
about 60,000 miles (more than 96,500 kilometers), which is far enough
to circle the earth more than twice!
See also on this site:
Updated June 2004
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