Anatomy of the Heart: Valves

Heart Valves
The valves of the heart: the tricuspid, bicuspid, two semilunar valves (foreground-background, respectively). The closed (left) and opened (right) positions of the valves are shown. MedicalRF.com/Getty Images

What Are Heart Valves?

Valves are flap-like structures that allow blood to flow in one direction. Heart valves are vital to the proper circulation of blood in the body. The heart has two kinds of valves, atrioventricular and semilunar valves. These valves open and close during the cardiac cycle to direct the flow of blood through the heart chambers and out to the rest of the body. Heart valves are formed from elastic connective tissue which provides the flexibility needed to open and close properly. Malfunctioning heart valves inhibit the heart's ability to pump blood and life giving oxygen and nutrients to the cells of the body.

Atrioventricular (AV) Valves

The atrioventricular valves are thin structures that are composed of endocardium and connective tissue. They are located between the atria and the ventricles.

  • Tricuspid Valve: This heart valve is located between the right atrium and the right ventricle. When closed, it allows oxygen-depleted blood returning to the heart from the venae cavae to fill the right atrium. It also prevents the back flow of blood as it is pumped from the right atrium to the right ventricle. When open, it allows blood from the right atrium to flow into the right ventricle.
  • Mitral Valve:┬áThis heart valve is located between the left atrium and left ventricle. When closed, it allows the left atrium to fill with oxygen-rich blood returning to the heart from the pulmonary veins. It opens to allow blood from the left atrium to fill the left ventricle.

Semilunar Valves

The semilunar valves are flaps of endocardium and connective tissue reinforced by fibers which prevent the valves from turning inside out. They are shaped like a half moon, hence the name semilunar (semi-, -lunar). The semilunar valves are located between the aorta and the left ventricle, and between the pulmonary artery and the right ventricle.

  • Pulmonary Valve: This heart valve is located between the right ventricle and pulmonary artery. When closed, it prevents the back flow of blood as it is pumped from the right ventricle to the pulmonary artery. When open, it allows oxygen-depleted blood to be pumped from the right ventricle to the pulmonary artery. This blood goes onto the lungs where it picks up oxygen.
  • Aortic Valve: This heart valve is located between the left ventricle and aorta. When closed, it allows blood from the left atrium to fill the left ventricle and prevents the back flow of blood that is pumped from the left ventricle to the aorta. When open, oxygen-rich blood can flow to the aorta and onto the rest of the body.

During the cardiac cycle, blood circulates from the right atrium to the right ventricle, from the right ventricle to the pulmonary artery, from the pulmonary artery to the lungs, from the lungs to the pulmonary veins, from the pulmonary veins to the left atrium, from the left atrium to the left ventricle, and from the left ventricle to the aorta and on to the rest of the body. In this cycle, blood passes through the tricuspid valve first, then the pulmonary valve, mitral valve, and finally the aortic valve. During the diastole phase of the cardiac cycle, the atrioventricular valves are open and semilunar valves closed. During the systole phase, the atrioventricular valves close and the semilunar valves open.

Heart Sounds

The audible sounds that can be heard from the heart are made by the closing of the heart valves. These sounds are referred to as the "lub-dupp" sounds. The "lub" sound is made by the contraction of the ventricles and the closing of the atrioventricular valves. The "dupp" sound is made by the semilunar valves closing.

Heart Valve Disease

When heart valves become damaged or diseased, they don't function properly. If valves don't open and close properly, blood flow becomes disrupted and body cells don't get the nutrient supply they need. The two most common types of valve dysfunction are valve regurgitation and valve stenosis. These conditions put stress on the heart causing it to have to work much harder to circulate blood. Valve regurgitation occurs when valves don't close correctly allowing blood to flow backward into the heart. In valve stenosis, valve openings become narrow due to enlarged or thickened valve flaps. This narrowing restricts blood flow. A number of complications may result from heart valve disease including blood clots, heart failure, and stroke. Damaged valves can sometimes be repaired or replaced with surgery.

Artificial Heart Valves

Should heart valves become damaged beyond repair, a valve replacement procedure can be performed. Artificial valves constructed from metal, or biological valves derived from human or animal donors can be used as suitable replacements for damaged valves. Mechanical valves are advantageous because they are durable and don't wear out. However, the transplant recipient is required to take blood thinners for life to prevent blood clot formation due to the tendency of blood to clot on artificial material. Biological valves can be derived from cow, pig, horse, and human valves. Transplant recipients are not required to take blood thinners, but biological valves can wear down over time.