BIOLOGY STPM SEM 2 NOTES

Sequence of Cardiac Cycle

Late Diastole

-         - Both atrial & ventricle are relaxed

-         -Blood is filling ventricle

-         -Atrioventricular valve open

-         -Volume of ventricle increase

-         -Pressure of atrial = pressure of ventricle

-         -Blood volume of atrial decrease

-         -Blood volume of ventricle increase

Atrial systole

-       - Atrial contraction

-       - Blood is filling ventricle

-       - Volume of ventricle increase

-       - Ventricle expand

-       - Pressure of atrial > pressure of ventricle

-       - Volume of atrial decrease

-       - Volume of ventricle increase 

Ventricle Systole

Isovolumetric ventricle contraction

-       -Ventricle start to contraction

-       -Blood pressure in ventricle increase

-       -Volume remain unchanged

-       -Blood pressure force atrioventricular valve closed when it > than atrial pressure

-       -Pressure not enough to open semilunar valve

-       -First ‘lub’ sound produced

-       -Both atrioventricular valve and semilunar valve closed

-       -Volume remains constant

-       -Pressure of ventricle > pressure atrial

-       -Pressure of ventricle < pressure of aorta

-       -Pressure of ventricle increase

Ventricle ejection

-       -Contraction of ventricle increase pressure dramatically

-       -As ventricle pressure > aortic pressure, semilunar valve open

-       -Blood pump by contracted ventricle to whole body through aorta

-       -Pressure and volume decrease

-       -Volume of ventricle decrease

-       -Pressure ventricle > pressure aorta

-       -Pressure ventricle

Isovolumic ventricle relaxation

-       -As ventricle repolarized, ventricle relax and pressure of ventricle decrease  

-       -As pressure of ventricle < pressure of atrial, semilunar valve closed

-       -Second ‘dub’ sound produced

-       -Both atrial and ventricle are relax

-       -When pressure of ventricle < pressure of atrial, atrioventricular valve open

-       -Blood flow into ventricle

-       -Volume of ventricle remain unchanged

-       -Pressure of aorta > pressure of ventricle

     -Pressure of atrial = pressure of ventricle 

    Initiate and Regulation of Heartbeat

SA node ( pacemaker ) generate impulses

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Impulses spread to both atrial wall

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Both atrial depolarized, contraction of atrial

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Impulse spread to atrioventricular node

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Delay 0.1 second

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Impulse spread to Bundle of HIS

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Bundle of HIS spread to purkinje fibre

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Depolarize ventricular wall, ventricle contract

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Ventricle repolarization, ventricle relax

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SA node generate nerve impulse, cycle start again