The valves of the heart are structures which ensure that blood travels through the heart in a single direction. They are composed of connective tissue and endocardium (the inner layer of the heart), and are divided into two categories - Atrioventricular valves and Semilunar valves. In this article, we will explore the anatomy of these valves, their structure, function, and their clinical correlations.
The atrioventricular valves are located between the atria and the ventricles. They close during the start of ventricular contraction (systole), producing the first heart sound. There are two Atrioventricular valves - the tricuspid valve and the mitral (bicuspid) valve. The tricuspid valve is located between the right atrium and right ventricle (right atrioventricular orifice). It is composed of three cusps – anterior, septal and posterior – with the base of each cusp secured to a fibrous ring that surrounds the orifice. The mitral valve is located between the left atrium and left ventricle (left atrioventricular orifice). This valve is also known as the bicuspid valve as it only has two cusps - anterior and posterior. Like the tricuspid valve, these cusps are connected to a fibrous ring that forms the orifice. These valves are also supported by fibrous cords (chordae tendineae), which are attached to the free edges of the valve cusps. The chordae tendineae attach to papillary muscles, located on the interior surface of the ventricles. These muscles contract during ventricular systole, to prevent the prolapse of valve cusps into the atria. In total, there are five papillary muscles – three are located in the right ventricle, and support the tricuspid valve; and two are located in the left ventricle, which control the mitral valve.
The semilunar valves are located between the ventricles and outflow vessels. They close at the beginning of ventricular relaxation (diastole), producing the second heart sounds. There are two Semilunar valves - the pulmonary valve and the aortic valve. The pulmonary valve is located between the right ventricle and the pulmonary trunk (pulmonary orifice). This valve consists of three cusps – left, right and anterior – named for their position in the foetus before the heart undergoes rotation. The aortic valve is located between the left ventricle and the ascending aorta (aortic orifice). It consists of three cusps - right, left and posterior. The left and right aortic sinuses mark the origin of the left and right coronary arteries. As blood recoils during ventricular diastole, it fills the aortic sinuses and enters the coronary arteries to supply the myocardium. Both of these valves have a similar structure, with the sides of each valve leaflet being attached to the walls of the outflow vessel, which is slightly dilated to form a sinus. The free superior edge of each leaflet is thickened (the lunule), and is widest in the midline (the nodule).
Aortic stenosis refers to narrowing of the aortic valve, which restricts the flow of blood out of the heart. The three main causes of aortic stenosis are age-related calcification, congenital defects such as a bicuspid aortic valve, and rheumatic fever. Severe aortic stenosis is characterized by a “classical triad” – shortness of breath, syncope, and angina.
The AV valves are divided into two types: tricuspid and mitral. The tricuspid valve is located between the right atrium and the right ventricle, also known as the right atrioventricular orifice. It consists of three cusps - anterior, septal and posterior - and the base of each one is anchored to a fibrous ring that surrounds the orifice.
The mitral valve is found between the left atrium and the left ventricle, with its location also known as the left atrioventricular orifice. This valve is sometimes referred to as the bicuspid valve because it has two cusps - anterior and posterior - with the base of each one attached to a fibrous ring. The base of the cusps is also supported by fibrous cords, known as chordae tendineae, which are then attached to papillary muscles on the interior surface of the ventricles. These muscles contract during ventricular systole to prevent prolapse of the valve leaflets into the atria. In total, there are five papillary muscles; three are found in the right ventricle and two in the left ventricle.
Semilunar valves are located between the ventricles and outflow vessels. They close at the beginning of ventricular relaxation (diastole), producing the second heart sound. There are two semilunar valves - the pulmonary valve and the aortic valve.
The left and right aortic sinuses mark the origin of the left and right coronary arteries. As blood recoils during ventricular diastole, it fills the aortic sinuses and enters the coronary arteries to supply the myocardium.
Aortic stenosis is a condition characterized by a narrowing of the aortic valve, and can be caused by a number of factors. Age-related calcification, congenital defects (most commonly a bicuspid aortic valve, which predisposes the valve to calcification later in life), and rheumatic fever are the main causes of aortic stenosis. Classic symptoms of the condition include shortness of breath, syncope, and angina. The increased workload for the left ventricle can cause left ventricular hypertrophy. Definitive treatment for aortic stenosis is usually surgical, and can be achieved through valve replacement or balloon valvuloplasty.
