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More About The Visible Heart
Front view without blood
The front view of the heart most clearly reveals the structure of this powerful
muscle. The heart has four chambers surrounded by thick muscular walls. In this
model, the right atrium (on your left) is shown in blue, the left atrium (on
your right) in yellow, the right ventricle in purple, and the left ventricle
in red. The chambers contain valves (shown in white) that prevent the blood
from flowing back inside once it has been pushed out. Click on the "Front view
with blood" link to see the blood in motion.
Front view with blood
Red and blue balls represent oxygenated and oxygen-depleted, or deoxygenated,
blood, respectively. By following the movement of these balls, you get a picture
of how blood flows from major blood vessels into the left and right atria and
then through the atrioventricular valves into the ventricles. From there, the
blood is pushed through the semilunar valves into major blood vessels leading
out of the heart. To take a closer look, click on the "Right heart with blood"
link.
Right heart with blood
Deoxygenated blood from the body enters the right atrium through two large
veins: the superior vena cava (top) and the inferior vena cava (bottom).
From the right atrium, blood passes through the tricuspid valve into the right
ventricle. From there it is pushed through the pulmonary valve into the main
pulmonary artery. The artery splits into left and right branches just above
the left atrium, with the left pulmonary artery sending blood to the left lung
and the right pulmonary artery (which snakes underneath the aortic arch and
around the back of the superior vena cava) sending blood to the right lung.
Left heart with blood
Directly underneath the pulmonary arteries, which send deoxygenated blood to
the lungs, are the pulmonary veins, which channel oxygenated blood from the
lungs back to the heart. Blood enters the left atrium from right and left pulmonary
veins and then passes through the mitral valve into the left ventricle. From
there, it is pushed through the aortic valve into the large aorta. The aorta
passes under the main pulmonary artery, arches over the left atrium, and then
travels down the rear of the heart, taking oxygen-rich blood to the legs and
internal organs. From the top of the aortic arch, three arteries—the brachiocephalic
artery, the left cartoid artery, and the left subclavian artery—branch
off to bring oxygenated blood to the head and arms.
Left heart valves
The mitral valve (so called because it resembles a bishop's miter) separates
the left atrium from the left ventricle. The valve consists of two cusps of
thin fibrous tissue, which form a hinge at the opening of the ventricle. As
the ventricle fills with blood, the two cusps are pushed together by the increasing
pressure inside the ventricle. At the other end of the valve, thin inelastic
tendons (called chordae tendineae) attach the valve to the fingerlike papillary
muscles of the ventricle. These attachments prevent the cusps of the valve from
folding back into the atrium when the valve closes. Blood rushing into the empty
ventricle from the atrium causes the valve cusps to open, and the cycle begins
once again.
Semilunar valves get their name from their crescent moon shape. The aortic
valve in the left heart is one of two semilunar valves; the other one is the
pulmonary valve located in the right heart. It regulates blood flow from the
left ventricle into the aorta. Its design is quite simple and effective: the
valve is made up of three small cusps attached to a ring at the base of the
aorta. When the ventricle is full of blood, the pressure causes each cusp to
become "pinched" toward the wall of the aorta, and this in turn causes the valve
to open. When the pressure in the ventricle drops, each cusp opens up again
and the valve closes. This prevents blood in the aorta from flowing back into
the ventricle.
Right heart valves
In the right heart, the tricuspid valve separates the atrium from the ventricle.
The valve has three cusps rather than the two found in the mitral valve of the
left heart. It gets its name from the toothlike shape these three cusps make
when the valve closes. Chordae tendineae, attach the tricuspid valve to the
papillary muscles that grow out of the wall of the ventricle.
In the large pulmonary artery, which takes the blood from the right ventricle
to the lungs, the pulmonary valve regulates the flow of blood in a similar fashion
to the aortic valve.
Visible Heart Background
The heart, central to life and health, pumps enough blood throughout the body
to fill a backyard swimming pool each week. The structure and function of the
heart are illustrated in this animation using a semitransparent, three-dimensional
heart. The flow of deoxygenated and oxygenated blood through the heart are shown
in separate modules to clarify unique structures and blood flow. The 3-D heart
rotates to provide optimal viewing. Heart valves are illustrated in connection
with blood flow. Further, comparisons are made between right and left ventricles
and between heart function and the tracings of an electrocardiogram. This animation
was designed in conjunction with HHMI's 1998 Holiday Lectures on Science, Of
Hearts and Hypertension: Blazing Genetic Trails.
Visible Heart Animation Tips
The animations in this section have a wide variety of classroom applications.
Use the tips below to get started but look for more specific teaching tips in
the near future. Please tell us how you are using the animations in your classroom
by sending e-mail to biointeractive@hhmi.org.
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Use the animations to make abstract scientific ideas visible and concrete.
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Explain important scientific principles through the animations. For example,
the biological clocks animations can be used to demonstrate the fundamentals
of transcription and translation.
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Make sure that students learn the material by repeating sections of the
animations as often as you think necessary to reinforce underlying scientific
principles. You can start, restart, and play back sections of the animations.
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Urge students to use the animations in accordance with their own learning
styles. Students who are more visually oriented can watch the animations
first and read the text later, while others might prefer to read the explanations
first and then view the graphics.
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Incorporate the animations into Web-based learning modules that you create
to supplement your classroom curricula.
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Encourage students to incorporate the animations into their own Web-based
projects.
Visible Heart Credits
Director: Dennis Liu, Ph.D.
Scientific Direction: Christine E. Seidman, M.D.
Scientific Content: Satoshi Amagai, Ph.D.
Animators: Eric Keller, Satoshi Amagai, Ph.D.
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