Heart Anatomy: Valve Structure and Function

1. Heart Valve Structure and Function

A transverse section through the heart slightly superior to the atrioventricular septum reveals all four heart valves along the same plane. The valves ensure unidirectional blood flow through the heart. Between the right atrium and the right ventricle is the right atrioventricular valve, or tricuspid valve. It typically consists of three flaps, or leaflets, made of endocardium reinforced with additional connective tissue. The flaps are connected by chordae tendineae to the papillary muscles, which control the opening and closing of the valves.

Emerging from the right ventricle at the base of the pulmonary trunk is the pulmonary semilunar valve, also known as the pulmonic valve or the right semilunar valve. The pulmonary valve consists of three small flaps of endothelium reinforced with connective tissue. When the ventricle relaxes, the pressure differential causes blood to flow back into the ventricle from the pulmonary trunk. This flow of blood fills the pocket-like flaps of the pulmonary valve, causing the valve to close and producing an audible sound. Unlike the atrioventricular valves, there are no papillary muscles or chordae tendineae associated with the pulmonary valve.

Located at the opening between the left atrium and left ventricle is the left atrioventricular valve, also called the mitral valve or bicuspid valve. Structurally, this valve consists of two cusps, compared to the three cusps of the right atrioventricular valve. In a clinical setting, the valve is referred to as the mitral valve, rather than the bicuspid valve. The two cusps of the mitral valve are attached by chordae tendineae to two papillary muscles that project from the wall of the ventricle.

At the base of the aorta is the aortic semilunar valve, or aortic valve, which prevents backflow from the aorta. It normally is composed of three flaps. When the ventricle relaxes and blood attempts to flow back into the ventricle from the aorta, blood will fill the cusps of the valve, causing it to close and producing an audible sound.

key concept

All four cardiac valves open and close based on the difference in pressure across the valve. When the direction of high to low pressure is also the direction that a valve opens, then it will open. However, when the direction of high to low pressure reverses, it causes the valve to close, restricting blood flow in the opposite direction.

The transverse section below shows the atrioventricular valves open and the semilunar valves closed. In this case, the pressure across the atrioventricular valves is higher in the atria and lower in the ventricle. Therefore, blood moves from the atria towards the ventricles and the AV valves open. The pressure across the semilunar valves is higher in the pulmonary trunk and aorta and lower in the ventricles. Therefore, blood moves back towards the ventricle and causes the flaps of the semilunar valves to lean against one another, shutting the valve.

Another transverse section below shows the valves in the opposite formation—the atrioventricular valves are closed and the semilunar valves are open. In this case, the pressure across the AV valves is higher in the ventricles and lower in the atria. Therefore, blood moves up towards the atria, closing the AV valves and restricting regurgitation of blood. The pressure across the semilunar valves is higher in the ventricles and lower in the pulmonary trunk and aorta. Therefore, blood moves towards the great vessels, and the valves open to allow the ejection of blood from the heart.

When the ventricles begin to contract, pressure within the ventricles rises and blood flows toward the area of lowest pressure, which is initially in the atria. This backflow causes the cusps of the atrioventricular valves to close. These valves are tied down to the papillary muscles by chordae tendineae. During the relaxation phase of the cardiac cycle, the papillary muscles are also relaxed and the tension on the chordae tendineae is slight. However, as the myocardium of the ventricle contracts, so do the papillary muscles. This creates tension on the chordae tendineae, helping to hold the cusps of the atrioventricular valves in place and preventing them from being blown back into the atria.

The aortic and pulmonary semilunar valves lack the chordae tendineae and papillary muscles associated with the atrioventricular valves. Instead, they consist of pocket-like folds of endocardium reinforced with additional connective tissue. When the ventricles relax and the change in pressure forces the blood toward the ventricles, the blood presses against these cusps and seals the openings.

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Please watch the following video for more information on this topic.

learn more

To see information about specific heart valve defects, please visit the supplemental document Disorders of Heart Valves.pdf.

IN CONTEXT

Career Connection
Cardiologist

Cardiologists are medical doctors that specialize in the diagnosis and treatment of diseases of the heart. After completing 4 years of medical school, cardiologists complete a three-year residency in internal medicine followed by an additional three or more years in cardiology. Following this 10-year period of medical training and clinical experience, they qualify for a rigorous two-day examination administered by the Board of Internal Medicine that tests their academic training and clinical abilities, including diagnostics and treatment. After successful completion of this examination, a physician becomes a board-certified cardiologist. Some cardiologists continue their training with additional fellowships, specializing in heart failure, cardiac intervention, electrophysiology (the electrical activity of the heart), and various types of imaging.

IN CONTEXT

Career Connection
Cardiovascular Technologist/Technician

Cardiovascular technologists/technicians are trained professionals who perform a variety of imaging techniques, such as sonograms or echocardiograms, used by physicians to diagnose and treat diseases of the heart. Nearly all of these positions require an associate degree. Growth within the field is fast, projected at 29% from 2010 to 2020.

There is a considerable overlap and complementary skills between cardiac technicians and vascular technicians, so the term cardiovascular technician is often used. Special certifications within the field require documenting appropriate experience and completing additional and often expensive certification examinations. These subspecialties include Certified Rhythm Analysis Technician (CRAT), Certified Cardiographic Technician (CCT), Registered Congenital Cardiac Sonographer (RCCS), Registered Cardiac Electrophysiology Specialist (RCES), Registered Cardiovascular Invasive Specialist (RCIS), Registered Cardiac Sonographer (RCS), Registered Vascular Specialist (RVS), and Registered Phlebology Sonographer (RPhS).