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Heart activity

Heart activity

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Heart activity

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  1. Heart activity • Changes in pressure and volume during the heart cycle

  2. The heart cycle • Period from the beginning of one heart beat to the beginning of the next heart beat • Two phases: • Diastole, period of cardiac muscle relaxation • Systole, period of cardiac muscle contraction • The atria and ventricles do not contract and relax at the same time.

  3. 5 phases of the heart cycle • Heart at rest (atrial and ventricular diastole) • Completion of ventricular filling (atrial systole) • Early ventricular contraction (first heart sound) • The heart pumps (ventricular ejection) • Ventricular relaxation (second heart sound)

  4. Heart at rest (atrial and ventricular diastole) • Atria and ventricles are relaxing • blood flows into the atria from veins • AV valves are open • Blood flows into the ventricles from the atria • Relaxed ventricles accept blood

  5. 2. Completion of ventricular filling (atrial systole) • Depolarization from the SA node • Contraction of atria • Blood pushed into the ventricles • Pressure increase accompanies contraction • Increase in pressure pushes some blood back to the veins

  6. 3. Early ventricular contraction (first heart sound) • Depolarization to AV node, down bundle of His, up Purkinje fibers • Ventricular systole begins at apex • Blood pushing up on AV pushes them shut • Blood does not flow back to atria • First heart sound when AV valves close (lub)

  7. 3. Early ventricular contraction (first heart sound) • The semilunar valves are also shut • Blood stays in the ventricle while it contracts • High pressure on the heart walls during this contraction •  ISOMETRIC CONTRATION

  8. 3. Early ventricular contraction (first heart sound) • Atria begin to repolarize and relax Atrial pressure falls below venous pressure • Blood flows from veins to atria  Blood stays in atria because the AV valves are closed

  9. 4. The heart pumps (ventricular ejection) • Ventricles contract • Semilunar valves open • Ventricular blood is pushed into the arteries

  10. 5. Ventricular relaxation (second heart sound) • Ventricular pressure falls • Blood starts to flow from arteries into ventricles • This backflow shuts the semilunar valves (dup of lub-dup) • Ventricles become closed • AV valves open when ventricular pressure is lower than atrial pressure

  11. End Diastole Volume (EDV) • Ventricles are maximally filled at the end of ventricular relaxation (diastole) • When heart rate is very high, the ventricles may not have enough time to fill as much as when the heart rate is slow

  12. End-systole volume (ESV) • The amount of blood left in the heart at the end of each contraction