The Cardiac Cycle Flashcards
What are steps of the cardiac cycle?
- Late diastole
- Atrial systole
- Ventricular systole
- Isometric volumetric contraction
- Ventricular Ejection phase
- Isometric volumetric relaxation
What does excitation-contraction couplinng allow?
The right part of the heart to depolarise and contract at the same time by stimulating the contraction of the heart
What is the state of systole and diastole duringg iso volumetric contraction?
Atrial diastole, ventricular systole
What is the state of systole and diastole during iso volumetric relaxation?
Ventricular diastole
What is the state of systole and diastole during ventricular ejection phase
Atrial diastole, ventricular systole
Describe In detail the events of the cardiac cycle.
- LATE DIASTOLE
- Towards the end of diastole, where sets of chambers are relaxed and the ventricles are filling passively - ATRIAL SYSTOLE
- Atria depolarise and contract , forcing a small amount of additional blood into the ventricles. - ISOVOLUMETRIC CONTRACTION
- Ventricle begins to contract and pressure builds up in the ventricle, rising higher than that of the atrium
- Mitral and triscupid valve shut.
- But pressure in ventricle doesn’t exceed that of the aorta/pulmonary trunk so aortic/PT valve remain closed. - VENTRICULAR EJECTION PHASE
- Pressure in ventricle continues to exceed as its still making cross bridges and exceeds that of the aorta/pulmonary trunk and aorta/pulmonary trunk valve opens.
- Blood is ejected out - ISOVOLUMETRIC RELAXATION
- The calcium thats released inside the ventricular muscle gets taken back up, less cross bridges are formed.
- Pressure in ventricles falls as the ventricle relaxes and falls below that of the aorta and Aortic valve closes
- Pressure in ventricles falls below that of the atrium, OPENING the mitral and tricuspid valve.
- Blood that has been accumulating in the atrium fills the ventricle passively,
- Last bit of filling- atria contract and pushes the last little bit of blood in the ventricle
Why does atria contract?
Pacemaker cells in the Sinoatrial node depolarises towards threshold and spreads a wave of depolarisation, therefore a wave of contraction across the atria.
Why does ventricle contract?
Ventricle is making cross bridges as calcium enters and interacts with contractile filaments in the ventricular muscle cell.
Describe the pressure changes in the left ventricle during the cardiac cycle.
ISOVOLUMETRIC CONTRACTION- Pressure In ventricle exceeds the pressure in the atrium, closing the mitral valve. Pressure in ventricle doesn’t exceed that of the aorta, so aortic valve is closed.
VENTRICULAR EJECTION-Pressure continues to increase In ventricle, exceeding that of the aorta and aortic valve opens.
- Ventricular pressure reaches peak pressure of 120mHg, then starts to fall.
ISOMETRIC RELAXATION- Ca is taken back up out of the cell, less cross bridges forming, pressure falls.
- Pressure continues to fall in the ventricle until it is smaller than that of the aorta, closing the aortic valve.
- Pressure continues to fall even more until pressure in ventricle is lower than that of the atrium, OPENING the mitral valve.
VENTRICULAR DIASTOLE- Atria begins to fill the ventricle with blood that has been building up inside the but pressure in ventricle remains low because it is big.
- little bit of blood- last bit of blood being expelled by the atria.
How much does systole and diastole take up at rest, and at exercise?
Systole 1/3, Diastole 2/3.
During exercise, diastoles shortens and systole takes up a larger proportion.
What is the pressure in atrium and aorta?
lOw pressure in atrium always and high pressure in aorta always
Describe the pressure changes in the left atrium during the cardiac cycle.
a- atria contracting (occurs after P wave)
c - ventricle contracting. Mitral valve pushing back into the left atrium but stops as soon as aortic valve opens. (occQRS)
v - Blood coming back from the lungs and accumulating in the atrium. (Atrium is small and accumulates in pressure)
Why is pressure so high in the aorta always?
the aorta is an elastic artery, it has lots of elastic energy.
Minimum diastolic pressure= 80
Maximum diastolic pressure=120.
What is the pulse pressure, but what is more significant?
The difference between the Maximum diastolic pressure and maximumm Systolic pressure (40mmHg)
- The average pressure throughout the whole cardiac cycle (Mean Arterial Pressure). In rough terms it is DIASTOLIC PRESSURE + 1/3 PULSE PRESSURE
Describe the pressure changes in the aorta during the cardiac cycle.
- When the aortic valve is open, the pressure of aorta follows the pressure of the left ventricle (i.e. seen during ventricular ejection phase, to peak 120mmHg then falling…)
- The dicrotic notch is, during relaxation the aortic valve shuts when ventricular pressure< it.It is the elastic recoil against which the aortic valve shuts.
