4. cardiac cycle final.pptx
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CARDIAC CYCLE
CARDIAC CYCLEDr. indrajeetDept. of prosthodontics
DEFINITIONThe cardiac events that occur from the beginning of one heartbeat to the beginning of the next are called the cardiac cycle.Each cycle is initiated by spontaneous generation of an action potential in the sinus node .
The heart is endowed with a special system for
(1) generating rhythmical electrical impulses to cause rhythmical contraction of the heart muscle
(2) conducting these impulses rapidly through the heart.
Division of cardiac cycle
Atrial systole & atrial diastole , ventricular systole & ventricular diastole7
Normal heart rate 72/minute
Duration of cardiac cycle -.8 sec
Duration of systole - .27 sec
Duration of diastole - .53 sec
ATRIAL SYSTOLE(LAST RAPID FILLING STAGE)Duration .11 secLast phase of ventricular diastole 10 % of blood is forced into ventricles
Atrial systole not essential during normal functioning helps during exercise.10
AV valves opened
Semilunarvalves closed
ISOMETRIC CONTRACTION PERIODDuration 0.05 secImmediately after atrial systoleA-v valves closed due to increased ventricular pressureSemilunar valves already closedContraction of ventricles without change in volume and length of muscle fibres
Significance explain to open semilunar valves12
AV valves closed
Semilunarvalves closed
EJECTION PERIODDuration is.22 secOpening of semilunar valvesEjection of blood from the ventriclesDivided into rapid ejection(0.13sec) & slow ejection(0.09sec)
AV valves closed
Semilunarvalves opened
PROTODIASTOLEDuration .04 secFirst stage of diastolePressure in aorta & pulmonary artery increases & in ventricles dropsSemilunar valves close
ISOMETRIC RELAXATION PERIODDuration - .08 secAll the valves are closedVentricles relax as closed cavitiesIntraventricular pressure fallsAV valves open
Significance explain opening of av valves17
Diastole: Period of isovolumic relaxation. Blood flowing back toward the relaxed ventricles causes the semilunar valves to close, which is the beginning of ventricular diastole. Note that the AV valves closed, also.
AV valves closed
Semilunarvalves closed
RAPID FILLINGDuration .11 secBlood collected in the atrium rapidly rushes into the ventriclesAbout 70 % of filling takes place
SLOW FILLINGDuration .19 sec Ventricular filling becomes slowThis slow filling is also called as diastasisAbout 20 % of filling occurs in this phase
AV valves opened
Semilunarvalves closed
INTRA ATRIAL PRESSURE CHANGES DURING CARDIAC CYCLEImportant for opening of AV valves & ventricular fillingLeft atrium 7-8 mm hgRight atrium 5-6 mm hg max0-2 mm hg - minimum
Intra Atrial pressure curveIt has three positive waves a,c,v
Three negative waves x,x1 ,y
a waveIt is the first positive wave and occurs during atrial systole
Pressure increases to 5 mm Hg in right atrium & 7 mm Hg in left atrium
x wave First negative wave & appears during the onset of atrial diastole
Pressure falls because of the relaxation of atriaAV valves close at the end of this wave
c wave Appears during isometric contractionRise in pressures is due to AV valve closureBulging of AV valves into atria
x1 waveAppears during ejection periodThe contraction of the ventricular musculature pulls the atrio ventricular ring towards the ventricles.
So fall in pressure28
v waveObtained during atrial diastole
Gradual increase in pressure due to filling of the atria
y waveApperas after opening of the AV valves Blood rushes to the ventriclesPressure in atria falls
Intraventricular pressure changes Maintenance of blood flow into systemic & pulmonary circulation depends upon the pressure at which the blood is pumped out of the ventricles.Right ventricle min 2-3 mm Hg max 25 mm Hg Left ventricle - min 5 mm Hg max- 120 mm Hg
Intra ventricular pressure curveA-B segmentB-C segmentC-D segmentD-E segmentE-F segmentF-G segmentG-A segment
Aortic pressure changesThe aortic pressure is responsible to maintain the blood flow through the circulating system.
PRESSURE SYSTEMIC AORTAPULMONARY ARTERYMAX PRESSURE 120 mm Hg 25 mm HgMIN PRESSURE 80 mm Hg 7-8 mm Hg
Volume of blood in right & left ventriclesMaximum volume of blood in each ventricle after filling is 150 ml .(End diastolic volume)
Minimum volume of blood after ejection period is about 70 ml . (End systolic volume)
ReferencesReview of medical physiology W.F Ganong 22nd editionText book of medical physiology guyton & hall 12th editionEssentials of medical physiology 2nd edition Sembulingam
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