The heart has four chambers. The upper chambers are known as the atria and the lower chambers are the ventricles. The atrium and ventricle on each side are separated by a valve, as are the exit points to the lungs and the body. The heart valves are flaps of cardiac tissue held in place by connective tissue anchored in the fibrous skeleton of the heart, called chordate tendineae. One valve is bicuspid, having two flaps, the others are tricuspid, having three flaps.
Atrioventricular Valves
The atrioventricular (AV) valves separate the atria and ventricles. Also known simply as the tricuspid valve, the right AV valve is a tricuspid valve separating the right atrium and right ventricle. When the right ventricle contracts, blood pushes against the valve forcing the flaps shut and preventing backflow into the atrium. When the ventricle relaxes, the flaps relax and blood can flow from the right atrium into the ventricle. The mitral valve, also known simply as the bicuspid valve, is the left AV valve separating the left atrium and left ventricle. Unlike the other AV valve, it only has two flaps, but it works in the same manner. The chordate tendineae extend from papillary muscles that react to the contraction of the left ventricle to keep the valve closed as the aortic valve opens.
Pulmonary Semilunar Valve
Blood is pumped from the right ventricle to the pulmonary artery on the way to the lungs. At this junction in the heart is the pulmonary semilunar valve, a tricuspid valve. The valve is forced open by the contraction of the right ventricle, and it is forced shut by the backflow of blood when the ventricle relaxes. The chordate tendineae supporting the valve extend from papillary muscles that contract with the right ventricle and prevent the valve flaps from inverting.
Aortic Semilunar Valve
Blood is pumped from the left ventricle through the aorta, the muscular blood vessel initiating the artery system. At this junction in the heart is the aortic semilunar valve, which opens when the left ventricle contracts. The valve closes when the ventricle relaxes.
Heart Valve Disease
Valvular disorders can be primary heart disease or secondary heart disease. Primary disorders are defects in the valve itself, either congenital or acquired. A thickened valve will prevent blood from moving forward, resulting additional heart malformations. Valve prolapse is the case of the valve leafs becoming floppy or stretched out, allowing blood to regurgitate. Regurgitation can result in the heart increasing its workload to keep up the cardiac output.
Secondary disorders are defects caused by the presence of another disease. Valve stenosis, the stiffening of the leaflets, can be caused by growths or scarring. Inflammation of the valves, called valvulitis, can lead to scarring or fibrosis, shrinking the valves and leaving a hole when they are closed. The stenotic valves are also not as flexible, causing problems with forward flow as well. Endocarditis is when growths form on the valves. The most common are calcium deposits or vegetative growths, caused by bacteria or autoimmune disease.
Defective heart valves often need to be replaced, usually with either pig valves or artificial components. Patients require immunosuppressive therapy to avoid the rejection of the replacements and monitoring to ensure deposition does not occur with the transplanted components.
References
Scanlon and Sanders. Essentials of Anatomy and Physiology, 4th ed. 2003. F. A. Davis Company.
Kumar, Cotran, Robbins. Basic Pathology, 7th ed. Saunders.
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