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:
- Atrial Systole: The atria contract, pushing blood into the ventricles through open AV valves.
- Ventricular Systole:
- AV valves close to prevent backflow.
- Semi-lunar valves open as ventricles contract and eject blood into the aorta and pulmonary artery.
- 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.