Valves are structures that ensure that fluids will pass through them in only one direction.
That is, a valve will open to allow fluids to pass in one direction but will close to prevent fluids from passing in the other direction.
There are two sets of cardiac valves--the atrioventricular (AV) valves and the semilunar valves.
Although the two sets of valves are quite different in design, they both function passively in response to the
flow of the blood.
Page 2 The AV Valves
The AV valves are found between the atria and the ventricles.
The AV valves consist of flaps, known as cusps.
The outer margin of each flap is attached to the inner surface of a fibrous ring.
The inner edge of each flap is free.
On the right side is the tricuspid valve.
On the left side is the mitral valve. ("Might is never right.")
Thus, the tricuspid valve is between the right atrium and the right ventricle. It is named for its three cusps.
The mitral valve is located between the left atrium and the left ventricle. Since it has two cusps, it is sometimes called the "bicuspid" valve.
Page 3 The AV Valves
The contraction of the atrial walls forces the blood from the atria through the AV valves and into the ventricles (atrial systole).
When the atria relax (atrial diastole) and the ventricles contract, the pressure would tend to drive the blood back into the atria.
However, each opening is sealed when the cusps of each AV valve meet in the valve center. This prevents blood from flowing further back into the atria.
Page 4 Chordae Tendineae
Chordae tendineae are a special anatomic arrangement which also helps prevent backward flow into the
Chordae tendineae are fibrous cords attached to the ventricular side of the cusps.
Since these cords of dense FCT have a fixed length, they cannot be stretched or shortened.
The other ends of these cords are attached to the papillary muscles.
The papillary muscles are special extensions of the muscular walls of the ventricles.
As theventricles contract and become smaller, these muscles take up the slack in the cords.
Page 5 Semilunar (Aortic and Pulmonary) Valves
As mentioned before, the bases of the two great arteries (the pulmonary arch and the aortic arch) begin at their respective ventricles as short cylinders of the fibrous skeleton.
Within each of these cylinders are three cuplike cusps, which make up each semilunar valve.
When the ventricles contract (ventricular systole) and the AV valves have closed, the blood moves
out into the great arteries through the semilunar valves.
When the ventricles relax (ventricular diastole), the back pressure of the blood in the great arteries forces the
cusps of the semilunar valves to the center and seals off each opening.