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Anatomy & Physiology (Open + Free)
Sy lla bu s
Unit 9:: The Cardiovascular System
Introduction to the
Cardiov ascular Sy stem
Module 34 /
Structures and Functions
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Valves of the Heart
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Describe the anatom ical
structures of the heart and
m ajor blood v essels entering and
leav ing the heart. Relate the
features of these structures to
blood flow into, out of, and
through the heart.
As mentioned earlier, blood flows through the heart in one direction. What prevents blood from flowing in the
opposite direction? The answer is the heart’s valves. These valves maintain unidirectional flow by preventing
backward (retrograde) flow when the pressure gradients change during the heart cycle. These valves are
found in matched pairs in two locations of the heart. The first set, the atrioventricular (AV) valves,
separate the atria from the ventricles. The second, the semilunar valves, are located between the
ventricles and the arteries they feed.
Following the path of blood flow through heart, the first valve is the tricuspid valve found separating the
right atrium from the right ventricle. This AV valve is so named because it has three flaps: the anterior
cusp, the medial cusp, and the posterior cusp. On the ventricle side of the valve are long muscular
cords, called chordate tendinae, that extend from the inferior side of each cusp. The chordate tendinae attach
to each cusp on one end and to the papillary muscle, which is connected to the inner wall of the ventricle,
on the other end. These muscles prevent the valves from inverting back into the atria during ventricular
contraction.
Figure 14
Most of the blood flows passively into the atria, through the tricuspid valve, and into the right ventricle. Atrial
contractions then push most of the remaining atrial blood into the ventricle. As the right ventricle fills, the
pressure inside it increases. This increased pressure, coupled with the right atria moving into its relaxation
phase, causes the ventricular pressures to be greater than atrial pressures. This causes the tricuspid AV
valves to close. In this closed position, the chordae tendinae that are attached to the ventricular side of the
valves are fully extended and taut, like a stretched bungee cord. The chordae tendinae prevent the higher
pressure in the ventricle from forcing the valve to open back into the atria, thus preventing the backflow of
blood through the tricuspid valve.
As the blood flows from the right ventricle into the pulmonary artery, it passes through the pulmonary
semilunar valve (pulmonary valve). Opposite to the tricuspid, the pulmonary semilunar valve remains
closed when the ventricle is filling and opens during ventricular contraction.Again, this is because the valves
work by opening when the pressure is higher on their proximal side and close when the pressure is higher on
their distal side.
On its return from the lungs, blood enters the left atrium. As the blood passes from the left atrium into the
left ventricle, it passes through the bicuspid valve, often referred to as the mitral valve. This valve is
similar in structure and function to the tricuspid, but only contains two cusps, the anterior and posterior
cusps. It, too, is open when the pressure in the atria exceeds the ventricle and it, too, has chordae tendinae
and papillary muscles that prevent its inversion upon ventricular contraction. The release of blood from the
left ventricle into the aorta is regulated by the aortic semilunar valve, which is most commonly referred
to as the aortic valve. It is similar in structure and function to the pulmonary semilunar valve. Because
they regulate the flow of blood through the heart and prevent its backflow, these valves are indispensable for
the proper function of the heart.
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Diseases of the Heart: Ruptured Chordae Tendinae
The chordae tendinae perform an important function by keeping the cusps of the atrioventricular valves
tethered to the interior wall of the ventricles. Without these tendons, and their associated papillary muscles,
the valves could become inverted when the pressure in the ventricle increases, causing the blood to rush back
into the atria.
Although this happens infrequently, the chordae tendinae can rip or rupture. When this happens, the cusps of
the tricuspid or mitral valves are no longer properly tethered to the wall of the ventricle. As the blood presses
back against the valves during ventricular contraction, the valves may not remain closed. If many of these
connections are ruptured or if the thicker ones are affected, the valves can open in the reverse direction, and
blood can backflow into the atria. This results in increased pressure in the atria and, if the backflow is
significant enough, congestive heart failure could develop.
Rupture of the chordae tendinae occurs when a patient suffers from a myocardial infarction (heart attack),
heart valve infection, or from trauma to the chest. Damage can range from minor to major depending on the
number of chordae affected. It is diagnosed by hearing a murmur, or a characteristic whooshing noise, upon
auscultation (listening to heart sounds with a stethoscope or other device) of the heart. Ruptured chordate
tendinae, and their associated conditions, commonly lead to heart failure.
Rupture of the chordae tendinae attached to the mitral valve is most common, although rupture of those
bound to the tricuspid valve can also occur. Rupture of the mitral valve chordae tendinae can result in a rapid
increase in left atrial pressure. This can subsequently increase the pressure in the pulmonary circulation,
ultimately producing pulmonary edema; which is retention of fluid in the lungs. An echocardiogram can
provide a more detailed look into the condition of the heart and the degree of damage to the chordae
tendinae.
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