Describe the functioning of the heart in terms of the contraction of muscles of the atria and ventricles and the action of the valves

The functioning of the heart involves a coordinated sequence of muscle contractions in the atria and ventricles, along with the precise action of the heart valves. This process ensures efficient blood circulation throughout the body. Here’s a detailed explanation of how these components work together:

Contraction of Muscles in the Heart

Atrial Contraction

1. Filling Phase: Blood returning from the body enters the right atrium via the superior and inferior vena cavae, while oxygenated blood returns to the left atrium from the lungs through the pulmonary veins.
2. Atrial Systole: Once filled, both atria contract simultaneously (atrial systole). This contraction is initiated by electrical impulses generated by the sinoatrial (SA) node, which serves as the heart’s natural pacemaker. The contraction forces blood through the open tricuspid valve into the right ventricle and through the mitral valve into the left ventricle.

Ventricular Contraction

1. Ventricular Filling: After atrial contraction, blood fills the ventricles during diastole (the relaxation phase).
2. Ventricular Systole: Following a brief pause to allow for complete filling, electrical signals travel to the atrioventricular (AV) node and then to the ventricles, causing them to contract simultaneously (ventricular systole). This contraction generates high pressure within the ventricles.

Action of the Valves

Atrioventricular Valves

• The tricuspid valve (right side) and mitral valve (left side) play a critical role during atrial and ventricular contractions:
  • During atrial systole, these valves open to allow blood flow from the atria into the ventricles.
  • As ventricular pressure rises during ventricular systole, these valves close tightly to prevent backflow of blood into the atria. This closure creates a distinct sound known as “lub” in the heartbeat.

Semilunar Valves

• The pulmonary valve (between right ventricle and pulmonary artery) and aortic valve (between left ventricle and aorta) control blood flow out of the ventricles:
  • When the ventricles contract, pressure forces these valves open, allowing deoxygenated blood to flow into the pulmonary artery for oxygenation in the lungs and oxygenated blood to flow into the aorta for distribution throughout the body.
  • Once ventricular contraction ends and pressure decreases, these valves close to prevent backflow of blood into the ventricles, producing a second sound known as “dub.”

Summary of Heart Functioning

1. Electrical Activation: The heart’s rhythm is initiated by electrical impulses that cause coordinated contractions of atria followed by ventricles.
2. Blood Flow Regulation: The opening and closing of valves ensure unidirectional blood flow—preventing backflow and maintaining efficient circulation.
3. Pressure Dynamics: The differences in pressure during contraction (systole) and relaxation (diastole) are crucial for effective pumping action.