Heart activity

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Heart activity

• Changes in pressure and volume during the heart
  cycle

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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.

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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)

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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

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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

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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)

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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

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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

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4. The heart pumps (ventricular ejection)

• Ventricles contract
• Semilunar valves open
• Ventricular blood is pushed into the arteries

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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

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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

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End-systole volume (ESV)

• The amount of blood left in the heart at the end
  of each contraction

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