Cardiac Cycle | Cardiovascular Physiology

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The Cardiac Cycle has three phases: Ventricular Filling, Ventricular Systole, and Isovolumetric Relaxation.
Ventricular Filling: The atrioventricular valves are open during ventricular filling because pressure is low in the heart. End diastolic volume (sometimes called preload) is the amount of blood that fills the ventricle before contraction begins.
Ventricular Systole: As contraction begins, the AV valves slap shut (LUB heart sound) due to building pressure in the ventricle. If someone has a heart murmur, there is a slight gurgling noise instead of a clear LUB and this may indicate a valve problem. Ventricular ejection occurs when the pressure has built up enough to overcome afterload (the pressure in the arteries) and open the SL valves. Stroke volume is the total amount of blood that is pumped in one beat; end systolic volume is the amount of blood remaining after the contraction. Ejection fraction is the percent of EDV that leaves the heart with beat (so it is equal to SV/EDV). Ejection fraction is notably decreased in congestive heart failure. According to the Frank-Starling Law of the Heart, SV increases in relation to increasing EDV. Ejection ends when the heart begins to relax, and the pressure is no longer high enough to hold open the SL valves. The closing of these valves is the "Dub" sound (second heart sound).
Isovolumetric Relaxation: The brief time when the heart is relaxing, but pressure is still too high to allow the AV valves to open, yet not high enough to keep the SL valves open.

[@yooksorts]

im reviewing for the teas and this is really helpful!! just a note for anyone checking the comments, it wasnt mentioned but the second heart sound "Dupp" is produced during isovolumetric relaxation w/ the closing of the SL valves! i think the first heart sound "Lubb", closing of the AV valves, was mentioned before. It's during the opposite aka, isovolumetric contraction/ventricular systole : ) (one way to remember: All Patients Take Medicine; Aortic and Pulmonic SL valve close=> second heart sound, Tricuspid and Mitral AV valve close=> first heart sound)
thank you again for the video!!

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