Heart As A Pump Flashcards
Define systole and diastole.
Systole= contraction and ejection of blood from ventricles. Diastole= relaxation and filling of ventricles.
What are the two pumps of the heart and their respective pressures?
Systemic circulation= High pressure, Pulmonary circulation= Low pressure.
Describe heart muscle and action potential.
A specialised form of muscle where cells contract in response to action potential in membrane. The AP causes a rise in intracellular calcium. Cardiac AP lasts for duration of a single contraction of heart (around 280ms).
How are APs triggered?
Triggered by spread of excitation from cell to cell.
What 4 valves determine the pathway of blood flow through heart?
Tricuspid valve (right, in), Pulmonary valve (right, out), Mitral valve (left, in), Aortic valve (left, out).
Describe the conduction system.
Pacemaker cells in sinoatrial node generate an AP. Activity spreads over atria (atrial systole), this reaches the AV node and is delayed around 120ms. Excitation spreads down septum between ventricles. Then it spreads through ventricular myocardium from inner to outer surface. The ventricle contracts from the apex up forcing blood through outflow valves.
What are the 7 phases of cardiac cycle?
Atrial contraction, isovolumetric contraction, rapid ejection, reduced ejection, isovolumetric relaxation, rapid filling and reduced filling.
Valve positions and blood flow for atrial contraction.
Mitral/Tricuspid: Open, Aortic/Pulmonary: Closed. Ventricular volumes are maximal (End-Diastolic Volume), around 120ml.
Valve positions and blood flow for isovolumetric contraction.
Mitral/Tricuspid: Closed, Aortic/Pulmonary: Closed. Isovolumetric since there is no change in ventricular volume.
Valve positions and blood flow for rapid ejection.
Mitral/Tricuspid: Closed, Aortic/Pulmonary: Open. Rapid decrease in ventricular volume as blood is ejected into aorta.
Valve positions and blood flow for reduced ejection.
Mitral/Tricuspid: Closed, Aortic/Pulmonary: Open. Rate of ejection begins to fall due to decline in tension.
Valve positions and blood flow for isovolumetric relaxation.
Mitral/Tricuspid: Closed, Aortic/Pulmonary: Closed. IV pressure falls below aortic pressure, brief back flow of blood causing aortic valve to close.
Valve positions and blood flow for rapid filling.
Mitral/Tricuspid: Open, Aortic/Pulmonary: Closed. IV pressure falls below atrial pressure, mitral valve opens and rapid ventricular filling begins.
Valve positions and blood flow for reduced filling.
Mitral/Tricuspid: Open, Aortic/Pulmonary: Closed. At rest the ventricles are around 90% full by the end.
What is stroke volume?
End Diastolic Volume - End Systolic Volume= Stroke Volume
