Cardiac Cycle Flashcards
Define isovolumetric contraction?
Ventricular contraction when all valves are closed. Increasing ventricular pressure but not volume
What produces first heart sound?
Closing of Mitral Valve due to LVp greater than LAp
What produces second heart sound?
Closing of aortic valve due to Aortic P greater than LVp
Describe events of systole?
Wave of depolarisation arrives, Ca2+ channels open.
LVp>LAp and the mitral valve closes.
LVp rises, isovolumetric contraction, LVp>aortic p.
Aortic valve opens and ejection begins.
Describe events of diastole.
LVp decreases and there is a phase of reduced ejection. LVp lower than aortic pressure and the aortic valve closes: isovolumetric ventricular relaxation.
LVp is less than LAp and mitral valve opens - ventricles fill with blood (Coronary arteries also fill).
Then begins again: Atria contract - atrial booster. LVp > LAp and mitral valve closes.
Duration of Systole and Diastole?
Systole: 0.3s Diastole: 0.5s
Define end systolic volume?
Volume of blood in LV following systole
Define preload
Volume in blood in ventricles before contraction (EDV)
Define afterload
Pressure against which heart must work to eject blood in systole
Define contractility
Inherent strength and vigour of hearts contraction during systole
Define Elasticity
Ability to recover original myocardial shape following contraction
Define compliance
How easily chamber of heart expands after filled with blood
What is the basic principle of Starling’s law of the heart?
Increased EDV = increased SV.
Explain Starling’s law.
The greater the EDV, the greater the sarcomeres are stretched and the more forceful the contraction.
With relation to Starling’s law, what is the effect of an increased venous return?
EDV will increase and so SV increases and so Cardiac output also increases as CO=SVxHR.
