The valves of the heart are structures which ensure blood flows in only one direction.They are composed of connective tissue and endocardium (the inner layer of the heart).
There are four valves of the heart, which are divided into two categories:
- Atrioventricular valves: The tricuspid valve and mitral (bicuspid) valve. They are located between the atria and corresponding ventricle.
- Semilunar valves: The pulmonary valve and aortic valve. They are located between the ventricles and their corresponding artery, and regulate the flow of blood leaving the heart.
In this article, we will look at the anatomy of these valves – their structure, function, and their clinical correlations
By OpenStax College [CC BY 3.0], via Wikimedia Commons
Fig 1
The four valves of the heart, visible with the atria and great vessels removed.
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Atrioventricular Valves
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 AV valves:
- Tricuspid valve – located between the right atrium and the right ventricle (right atrioventricular orifice).Itconsists ofthree cusps (anterior, septal and posterior), withthe base of each cusp anchoredto a fibrous ring that surrounds the orifice.
- Mitral valve –located between the left atrium and the left ventricle (left atrioventricular orifice).It is also known as thebicuspid valvebecause it has two cusps (anterior andposterior). Like the tricuspid valve, thebase of each cusp is securedtofibrous ring that surrounds the orifice.
The mitral and tricuspid valvesare supported by the attachment of fibrous cords (chordae tendineae) to the free edges of thevalve cusps. The chordae tendineae are, in turn, attachedto papillary muscles,located on the interior surface of the ventricles – these muscles contract during ventricular systole to prevent prolapse of the valve leafletsinto the atria.
There are five papillary muscles in total. Three are located in the right ventricle, and support the tricuspid valve. The remaining two are located within the left ventricle, and act on the mitral valve.
By TeachMeSeries Ltd (2024)
Fig 2
The papillary muscles and inflow portion of the left ventricle.
Semilunar Valves
The semilunarvalves are located between the ventricles and outflow vessels.They close at the beginningofventricular relaxation(diastole), producing the second heart sounds. There are two semilunar valves:
- Pulmonary valve – located between the right ventricle and the pulmonary trunk (pulmonary orifice).The valve consists ofthreecusps – left, right andanterior (named by their position in the foetus before the heart undergoes rotation).
- Aortic valve – located between the left ventricle and the ascending aorta (aortic orifice).The aortic valveconsists of threecusps – right, leftandposterior.
- The left and right aortic sinuses mark the origin of the left and right coronary arteries. As blood recoils during ventricular diastole, it fills theaortic sinuses and enters the coronary arteries to supply the myocardium.
The pulmonary and aortic valves have a similar structure. The sides of each valve leaflet are attached to the walls of the outflow vessel, which is slightly dilated to form a sinus. The free superior edge of each leafletis thickened (the lunule), and is widestin the midline (the nodule).
At the beginning of ventricular diastole, blood flows back towards the heart, filling the sinuses and pushing the valve cusps together. This closes the valve.
By TeachMeSeries Ltd (2024)
Fig 3
The aortic valve cusps, aortic sinuses, and the origin of the coronary arteries.
Clinical Relevance
Aortic Stenosis
Aortic stenosis refers to narrowing of the aortic valve, restricting the flow of blood leaving the heart. The main three causes are:
- Age-related calcification
- Congenital defects
- Most commonly a bicuspid aortic valve, which predisposes the valve to calcification later in life.
- Rheumatic fever
The classical triad seen insevere aortic stenosis is shortness of breath, syncope and angina. The increasing workload for the left ventricle can also result in left ventricular hypertrophy.
Definitive treatment is surgical, and can be achieved via valve replacement or balloon valvuloplasty.
By TeachMeSeries Ltd (2024)
Fig 4
Aortic stenosis, secondary to rheumatic heart disease. The aorta has been removed to show thickened, fused aortic valve leaflets and opened coronary arteries from above.
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