Illustrate the structure of heart. Explain the steps of cardiac cycle.

Illustrate the Structure of Heart. Explain the Steps of Cardiac Cycle

Structure of the Heart

The human heart is a muscular organ located in the thoracic cavity between the lungs. It has four chambers:

• Two atria (right and left atrium) – thin-walled chambers that receive blood.
• Two ventricles (right and left ventricle) – thick-walled chambers that pump blood.

Valves ensure unidirectional blood flow:

• Tricuspid valve – between right atrium and right ventricle
• Bicuspid/Mitral valve – between left atrium and left ventricle
• Pulmonary valve – between right ventricle and pulmonary artery
• Aortic valve – between left ventricle and aorta

Steps of the Cardiac Cycle

The cardiac cycle represents one complete heartbeat and includes:

1. Atrial Systole: The atria contract, pushing blood into the ventricles through open AV valves.
2. Ventricular Systole:
   • AV valves close to prevent backflow.
   • Semi-lunar valves open as ventricles contract and eject blood into the aorta and pulmonary artery.
3. Diastole: The heart muscle relaxes.
   • Blood flows from veins into atria.
   • AV valves open to refill ventricles.

The complete cardiac cycle lasts about 0.8 seconds in a healthy adult.