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Cardiac cycle (Cardiac Cycle (Reduced Ventricular Ejection (Ejection…
Cardiac cycle
Cardiac Cycle
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Isovolumetric relaxation
- Ventricles begin relax
- AV and SL valves both closed
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Reduced passive filling
- Diastasis: Might occur when heart rate increased (e.g. tachycardia)
Atrial systole
- Left and right atria contract + blood ejected into ventricles via AV valves
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Electrophysiology
- Cardiac cells divided two cats: nodal cells + cardiac myocytes
Nodal cells: initiating wave of excitation, passes through cells by gap junctions, into myocytes, allow contraction of heart
- Excitation nodal cells dominated L-type Ca2+ channels
- Excitation of cardiac myocytes dominated by Voltage gated Na+ channels
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Conduction system
- Heart rate under hormonal control or autonomic control
sympathetic NS: increase heart rate
Parasymp NS: decrease heart rate
- Depolarization (Automaticity) sino-atrial node
- Gap junctions, wave of depolarization to neighbor cells
- Depolarisation of both atria in coordinated way: Bachmann's bundle
- AV node: only connection between atria and ventricles through internodal tracts
- AV node delay:
- Bundle HIS
Left posterior fascicle, left anterior fascicle (left bundle) + right bundle
- Purkinje Fibres
- Adjacent myocytes attached end to end stepped face, the intercalated disc
- Gap junction stransmit electrical current between myocytes
- Desmosomes provide mechanical strength
- Automaticity: initiate electrical impulse
- Excitability: Respond to electrical impulse
- Conductivity: transmit electrical impulse form one cell to another
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Pressure Aortic valve
- Drifting down, Blood rushing away, pressure falls
- When aortic pressure < LV pres
AV closed + Semilunar valve opened
- Pres starts rising, follows course LV
- Muscle repolarises
- Pres decreases
- Aorta > LV, Semilunar valve close.
- Slow decrease pres
Compliance
- Aortic vessels are 'stretchable'
- Blood pushes against walls which stretch
- increase Aortic pressure: maximal stretching walls
- Aortic press > Lv press as: Blood vessels recoil (passive + elastic): Valves snap shut
- Blood that hits off the aortic valve ('snapback'): Slight increase press DICROTIC NOTCH
Left Atria
- Mitral valve open
Blood from LA to LV
- Atrial systole (A wave)
- Ventricular contraction
Mitral valve closes
- Blood crashing off Mitral valve
Increase press LA (C wave)
- LA fill up blood, press rising
- LA>LV
Mitral valve opens
V wave: very full LA
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Pressure left ventricle
- Initial slow increase: Blood moving in
- Depolarisation wave: muscle contraction (+RV)
- Pressure rises, LV pres > LA pres,
AV valves close (S1 LUB)
Semilunar closed
- Rapid rise pressure
- When LV > Aortic pres, blood enters =
AV closed
Semilunar valve opened
- Pres continues rising
- Muscle repolarises
- Pres decreases: Lots of resistance in blood vessels = pres remains high
- LV< Aorta:
Semilunar valve close (S2 DUB)
AV valve closed
- Pres almost gets to 0 before LA > LV,
AV valves open
Semilunar valve closed
slow increase press
Waves
- P wave (P-middle QRS):
Muscular contraction atrium : atrial systole
- QRS: depolarisation of ventricular myocardium
inititate contraction of Vent myocardium
- T wave:Repolarisation of Ventricle
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