Cardiac Cycle PDF

Cardiac cycle  The Heart two pumps in series each side consists of – thin walled atrium – muscular ventricle flows into and out of ventricle controlled by valves – atrioventricular valves (mitral & tricuspid) – outflow valves (aortic and pulmonary)  Hea...

Cardiac cycle  The Heart two pumps in series each side consists of – thin walled atrium – muscular ventricle flows into and out of ventricle controlled by valves – atrioventricular valves (mitral & tricuspid) – outflow valves (aortic and pulmonary)  Heart Muscle a specialised tissue discrete cells connected electrically - syncytium cells contract when action potential in membrane reaches threshold  Heart Muscle action potential causes a rise in intracellular calcium action potential long - single contraction lasts 280 ms - systole action potentials triggered by spread of excitation from cell to cell  Pacemakers an action potential generated in a small group of cells will spread over the whole heart and produce a coordinated contraction pacemakers generate one action potential at regular intervals  Phases of the Cardiac Cycle each action potential produces one beat - systole interval between beats known as diastole  Spread of excitation -1 pacemaker in sino- atrial node - right atrium 1 activity first spreads over the atria - atrial systole to reach the atrio- ventricular node, where delayed for about 120 ms  Spread of excitation - 2 from a-v node spreads down the septum between the ventricles then spreads through 4 the ventricular myocardium from inner 2 (endocardial) to outer (epicardial) surface ventricle contracts from the apex up, forces blood towards the outflow valves 3  The Cardiac Cycle at rest the SA node generates an action potential about once a second this produces a short atrial systole followed by a longer ventricular systole ventricular systole last about 280 ms followed by a relaxation lasting about 700 ms before the next systole  Ventricular pumping the combination of regular alternating systole and diastole with inflow and outflow valves allows the heart to work a a reciprocating pump the ventricles fill from the veins in diastole the ventricles pump blood into arteries in systole  The Left Ventricle inflow valve - the mitral valve – allows blood from the atrium to ventricle, but not vice-versa opens when atrial pressure exceeds intraventricular pressure closes when ventricular pressure exceeds atrial pressure  The Left Ventricle outflow valve - the aortic valve – allows blood from the ventricle to the aorta, but not vice-versa opens when intra-ventricular pressure exceeds aortic pressure closes when aortic pressure exceeds ventricular pressure  The Cardiac Cycle - 1 start towards the end of ventricular systole – ventricles contracted Pressure – intra-ventricular pressure high – outflow valves open – blood flowing into the arteries – ventricular pressure > Volume atrial pressure so a/v Aorta valves closed Ventricle Atrium  The Cardiac Cycle - 2 ventricles begin to relax – intra ventricular pressure falls Pressure – intra-ventricular pressure becomes < arterial – brief backflow closes outflow valves – all valves now closed – get isovolumetric Volume relaxation Aorta Ventricle Atrium  The Cardiac Cycle - 3 during systole blood has continued to return to the atria Pressure – atrial pressure relatively high – as intra-ventricular pressure falls, eventually, – atrial pressure > intra- venticular pressure Volume – so a/v valves open Aorta Ventricle Atrium  The Cardiac Cycle - 4 with the a/v valves open ventricles – fill rapidly - ‘rapid Pressure filling phase’ – lasts about 200-300 ms – most filling of ventricles occurs in Volume this phase Aorta Ventricle Atrium  The Cardiac Cycle - 5 as diastole continues the ventricles fill more slowly Pressure – intraventricular pressure rises as the ventricular walls stretch – until intra-ventricular pressure matches atrial, and filling stops Volume Aorta Ventricle Atrium  The Cardiac Cycle - 6 atrial systole – forces a small extra amount of blood into Pressure the ventricles – but the heart pumps perfectly well without atrial systole Volume Aorta Ventricle Atrium  The Cardiac Cycle - 7 ventricular systole – intraventricular pressure rises very rapidly Pressure – quickly exceeds atrial pressure – so after brief backflow a/v valves close – all valves closed – get isovolumetric Volume contraction Aorta Ventricle Atrium  The Cardiac Cycle - 8 intraventricular pressure rises very rapidly Pressure – until intra-ventricular pressure > arterial pressure – which has been falling in diastole – so outflow valves Volume open Aorta Ventricle Atrium  The Cardiac Cycle - 9 as outflow valves open – blood is ejected Pressure rapidly into the arteries – rapid ejection phase – arterial pressure rises rapidly Volume Aorta Ventricle Atrium  The Cardiac Cycle - 10 as arterial pressure rises – the rate of ejection of Pressure blood falls – both arterial and intraventricular pressures peak towards the end of systole – outflow eventually ceases wih blood still in Volume Aorta ventricle Ventricle Atrium  The Cardiac Cycle - 11 eventually, systole ends – and back to 1 Pressure Volume Aorta Ventricle Atrium