Lub Dub | Coconote

Overview

This lecture explains the origins of heart sounds ("lub dub") by detailing the function of the heart's valves during the cardiac cycle.

The heart has four chambers: right atrium, right ventricle, left atrium, left ventricle.
Blood flows from the right atrium to right ventricle, then to the lungs, returns to the left atrium, and enters the left ventricle.
Four valves regulate blood flow: tricuspid (right atrium to right ventricle), pulmonary (right ventricle to lungs), mitral (left atrium to left ventricle), aortic (left ventricle to aorta).

Valves prevent backflow by opening and closing in response to blood movement.
When ventricles fill, tricuspid and mitral valves are open, pulmonary and aortic valves are closed.
When ventricles contract (squeeze), pulmonary and aortic valves open to allow blood out; tricuspid and mitral valves close to stop backflow.

"Lub" (S1) is created when the tricuspid and mitral valves snap shut at the start of ventricular contraction.
"Dub" (S2) is produced when pulmonary and aortic valves snap shut at the end of ventricular contraction.
The cycle repeats as the valves alternate opening and closing.

Systole: period between "lub" and "dub" when ventricles contract and blood is pumped out.
Diastole: period between "dub" and the next "lub" when ventricles relax and refill with blood.

Tricuspid Valve — valve between right atrium and right ventricle.
Mitral Valve — valve between left atrium and left ventricle.
Pulmonary Valve — valve from right ventricle to pulmonary artery/lungs.
Aortic Valve — valve from left ventricle to aorta.
S1 ("lub") — first heart sound, caused by closure of tricuspid and mitral valves.
S2 ("dub") — second heart sound, caused by closure of pulmonary and aortic valves.
Systole — phase when the heart contracts to pump blood out.
Diastole — phase when the heart relaxes and fills with blood.