M01.05.018 The Valves of the Heart

Heart valves play a crucial role in ensuring the unidirectional flow of blood through the chambers of the heart. They are composed of connective tissue and endocardium, the inner layer of the heart. There are four main valves, categorized based on their location and function:

Categories of Heart Valves

There are two main types of heart valves:

1. Atrioventricular (AV) Valves

• Tricuspid Valve: Between the right atrium and right ventricle.
• Mitral (Bicuspid) Valve: Between the left atrium and left ventricle.

2. Semilunar Valves

• Pulmonary Valve: Between the right ventricle and pulmonary trunk.
• Aortic Valve: Between the left ventricle and ascending aorta.

Key Features of Heart Valves

Anatomy and Function of Atrioventricular Valves

Tricuspid Valve

• Location: Between the right atrium and right ventricle.
• Structure: Three cusps (anterior, septal, posterior).
• Function: Closes during ventricular contraction (systole) to prevent blood from flowing back into the right atrium.

Mitral Valve

• Location: Between the left atrium and left ventricle.
• Structure: Two cusps (anterior and posterior).
• Function: Closes during ventricular contraction (systole) to prevent blood from flowing back into the left atrium.

Support Structures:

• Chordae Tendineae: Fibrous cords that attach to the valve cusps and prevent prolapse.
• Papillary Muscles: Contract during systole to prevent valve prolapse. There are five papillary muscles:
  • Three in the right ventricle (supporting the tricuspid valve).
  • Two in the left ventricle (supporting the mitral valve).

Anatomy and Function of Semilunar Valves

Pulmonary Valve

• Location: Between the right ventricle and pulmonary trunk.
• Structure: Three cusps (left, right, anterior).
• Function: Closes during diastole to prevent blood from flowing back into the right ventricle.

Aortic Valve

• Location: Between the left ventricle and ascending aorta.
• Structure: Three cusps (right, left, posterior).
• Function: Closes during diastole to prevent blood from flowing back into the left ventricle.

Aortic Sinuses:

• Function: The sinuses fill with blood during diastole, supplying the coronary arteries with oxygenated blood for the myocardium.

Clinical Relevance

1. Aortic Stenosis

Aortic stenosis refers to the narrowing of the aortic valve, which impedes the flow of blood from the left ventricle into the aorta. The three main causes of aortic stenosis are:

• Age-related calcification: Accumulation of calcium on the valve.
• Congenital defects: Bicuspid aortic valve is more prone to calcification.
• Rheumatic fever: Leads to fibrosis and scarring of the valve.

Classic Symptoms of Severe Aortic Stenosis

• Shortness of breath
• Syncope (fainting)
• Angina (chest pain)

Complications

• Left Ventricular Hypertrophy: Due to increased workload on the left ventricle.

Treatment

• Surgical Options: Valve replacement or balloon valvuloplasty.

Points to Remember

• Heart valves ensure the one-way flow of blood.
• The AV valves (tricuspid and mitral) are between the atria and ventricles, while the semilunar valves (pulmonary and aortic) are between the ventricles and outflow vessels.
• The first heart sound (S1) is caused by the closure of the AV valves, while the second heart sound (S2) is due to the closure of the semilunar valves.
• The chordae tendineae and papillary muscles prevent valve prolapse during ventricular contraction.
• Aortic stenosis is a common valve disorder that can lead to significant clinical consequences, requiring timely intervention.