Valves of the Heart

Atrioventricular (AV) Valves

The atrioventricular valves are critical structures that separate the atria from the ventricles, ensuring unidirectional blood flow through the heart.

• Function: All heart valves act as one-way "push doors", opening when pushed from one direction and closing when pushed from the other, thus preventing backflow of blood.

• Tricuspid Valve: Connects the right atrium to the right ventricle and consists of three cusps (flaps).

• Bicuspid (Mitral) Valve: Connects the left atrium to the left ventricle and consists of two cusps. Also known as the mitral valve.

Key Mechanisms:

• When the atria contract and the ventricles relax, AV valves open as blood pressure from the atria pushes the cusps open.

• When the ventricles contract, AV valves close as blood pressure pushes the cusps upward and shut.

• Papillary muscles and chordae tendineae prevent the cusps from swinging back into the atria, thus preventing regurgitation (backflow of blood).

Semilunar Valves

The semilunar valves are located at the exits of the ventricles and prevent blood from flowing back into the heart after contraction.

• Consist of cusps (flaps) shaped like half-moons.

• Pulmonary Semilunar Valve: Located between the right ventricle and the pulmonary trunk. Prevents backflow as blood flows from the right ventricle to the pulmonary trunk.

• Aortic Semilunar Valve: Located between the left ventricle and the ascending aorta. Prevents backflow as blood flows from the left ventricle to the aorta.

Valve Dynamics:

• When ventricles contract, semilunar valves open as increasing pressure in the ventricles overcomes the pressure in the aorta and pulmonary trunk.

• When ventricles relax, semilunar valves close as blood pressure in the arteries keeps them shut, preventing backflow into the ventricles.

Circulatory Pathways

Pulmonary Circuit

The pulmonary circuit is responsible for transporting blood between the heart and the lungs for gas exchange.

• Carries deoxygenated blood from the right ventricle to the lungs via the pulmonary arteries.

• Returns oxygenated blood from the lungs to the left atrium via the pulmonary veins.

Systemic Circuit

The systemic circuit delivers oxygenated blood from the heart to the rest of the body and returns deoxygenated blood back to the heart.

• Carries blood from the left ventricle through the aorta to the body tissues.

• Returns deoxygenated blood to the right atrium via the superior and inferior vena cava.

• Blood must alternate between pulmonary and systemic circuits to maintain efficient oxygenation and nutrient delivery.

Coronary Circuit

The coronary circuit supplies oxygen and nutrients to the heart tissue itself.

• Begins at the coronary arteries branching from the base of the aorta.

• Right coronary artery: Supplies the right side of the heart, including the posterior interventricular artery and right marginal branch.

• Left coronary artery: Supplies the left side of the heart, including the circumflex branch and anterior interventricular artery (LAD).

Blood Flow to the Heart and Clinical Relevance

Coronary Blood Flow

Blood flow through the coronary arteries is essential for myocardial (heart muscle) health.

• Ischemia: Decrease in blood flow due to partially blocked artery, leading to reduced oxygen supply to myocardial cells.

• Angina pectoris: Painful condition caused by oxygen deprivation of myocardial cells.

• Myocardial infarction (heart attack): If total blockage occurs (e.g., coronary thrombosis), heart tissue will die due to lack of oxygen.

• Blood flow in coronary arteries lessens during contraction (systole) and peaks during relaxation (diastole), as contraction compresses these vessels.

Summary Table: Heart Valves

Key Terms and Definitions

• Ischemia: Reduced blood supply to tissues, causing a shortage of oxygen and nutrients.

• Angina pectoris: Chest pain due to temporary ischemia of the myocardium.

• Myocardial infarction: Death of heart muscle tissue due to prolonged lack of oxygen (heart attack).

• Regurgitation: Backflow of blood due to valve failure.

• Chordae tendineae: Tendinous cords that anchor AV valve cusps to papillary muscles.

• Papillary muscles: Muscles in the ventricles that contract to prevent AV valve prolapse.

Example Application

• Clinical Example: If the chordae tendineae are damaged, the AV valves may prolapse, leading to regurgitation and reduced cardiac efficiency.

• Pathway Example: Blood flows from the right atrium → tricuspid valve → right ventricle → pulmonary semilunar valve → pulmonary trunk → lungs (pulmonary circuit).

Brain Check (Review Questions)

• The system of vessels carrying blood to and from the lungs is called the pulmonary circuit.

• Blood entering the systemic circuit would be oxygen-rich.