Overview
This lecture explains the origins of heart sounds ("lub dub") by focusing on heart valves and the cardiac cycle, including systole and diastole.
Heart Chambers and Blood Flow
- The heart has four chambers: right atrium, right ventricle, left atrium, and left ventricle.
- Blood flows from the right atrium → right ventricle → lungs → left atrium → left ventricle.
- Blood moves simultaneously on both sides through coordinated cycles.
Heart Valves and Their Roles
- The heart contains four valves: tricuspid, pulmonary, mitral, and aortic valves.
- Tricuspid and mitral valves are open during ventricular filling; pulmonary and aortic are closed.
- Valves prevent backflow by closing in response to incorrect flow direction.
Origin of Heart Sounds (Lub Dub)
- When ventricles are full and the tricuspid/mitral valves close, the first heart sound (S1 or "lub") is produced.
- Closure of these valves prevents blood from moving backward into the atria.
- After ventricular contraction, the aortic and pulmonary valves close, producing the second heart sound (S2 or "dub").
- Closure of these valves prevents backflow from arteries into the ventricles.
Timing in the Cardiac Cycle
- The interval between S1 (lub) and S2 (dub) is called systole, when the heart pumps blood out.
- The interval between S2 (dub) and the next S1 (lub) is called diastole, when the heart refills with blood.
Key Terms & Definitions
- Tricuspid valve — separates right atrium from right ventricle.
- Pulmonary valve — separates right ventricle from pulmonary artery.
- Mitral valve — separates left atrium from left ventricle.
- Aortic valve — separates left ventricle from aorta.
- S1 (First heart sound/lub) — sound made by closure of tricuspid and mitral valves.
- S2 (Second heart sound/dub) — sound made by closure of aortic and pulmonary valves.
- Systole — phase when ventricles contract and pump blood out.
- Diastole — phase when ventricles relax and fill with blood.
Action Items / Next Steps
- Review diagrams of the heart to identify all four chambers and valves.
- Practice labeling the timing of S1 and S2 on a cardiac cycle diagram.