The heart is a vital organ in the human body responsible for pumping blood throughout the circulatory system. It consists of several chambers, valves, and blood vessels that work together to ensure efficient blood circulation.

Structure of the Heart:

Atria: The heart has four chambers, with two upper chambers called atria (singular: atrium). The right atrium receives deoxygenated blood from the body through the superior and inferior vena cava, while the left atrium receives oxygenated blood from the lungs through the pulmonary veins.

Ventricles: The lower chambers of the heart are called ventricles. The right ventricle pumps deoxygenated blood into the pulmonary artery, which carries it to the lungs for oxygenation. The left ventricle, which is more muscular, pumps oxygenated blood into the aorta, which distributes it throughout the body.

Valves: The heart has four valves that ensure one-way blood flow:

Tricuspid Valve: Located between the right atrium and right ventricle.

Pulmonary Valve: Located between the right ventricle and the pulmonary artery.

Mitral Valve (Bicuspid Valve): Located between the left atrium and left ventricle.

Aortic Valve: Located between the left ventricle and the aorta.

Septum: The septum is a muscular wall that separates the right and left sides of the heart, preventing the mixing of oxygenated and deoxygenated blood.

Cardiac Cycle:

The cardiac cycle is a series of events that occur during one heartbeat, including the contraction (systole) and relaxation (diastole) phases. It can be divided into several phases:

Atrial Contraction (Atrial Systole): The cardiac cycle begins with the contraction of the atria, which forces blood into the ventricles. The atrioventricular (AV) valves (tricuspid and mitral) are open during this phase.

Ventricular Contraction (Ventricular Systole): Once the ventricles are filled with blood, they contract, causing the AV valves to close and the semilunar valves (pulmonary and aortic) to open. This action forces blood into the pulmonary artery and aorta, sending oxygenated blood to the lungs and the rest of the body.

Isovolumetric Relaxation: After ventricular contraction, the ventricles relax briefly. All heart valves are closed during this phase, preventing backflow of blood.

Atrial Filling (Atrial Diastole): As the ventricles relax, the atria begin to fill with blood from the superior and inferior vena cava and pulmonary veins. This phase completes the cardiac cycle.

The cardiac cycle repeats continuously, ensuring a continuous flow of blood through the heart and the entire circulatory system, providing oxygen and nutrients to body tissues while removing waste products.

This process is regulated by electrical signals generated by the heart’s conduction system, specifically the sinoatrial (SA) node, atrioventricular (AV) node, and Purkinje fibers, which coordinate the rhythmic contractions of the heart muscle. These electrical impulses initiate and control each heartbeat.