Cardiac Cycle NOTES

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• Cardiac Cycle NOTES

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The Cardiac Cycle

• The primary function of the heart is to circulate
  oxygenated and deoxygenated blood throughout the
  body.

• The RIGHT chambers of the heart carry
  deoxygenated blood to travel to the lungs, where
  it RELEASES CO2 and RECEIVES O2
• The LEFT chambers pump oxygenated blood back to
  the bodys organs and muscles

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REVIEW PATHWAY OF BLOOD THROUGH THE HEART

• Blood low in oxygen from the body returns to the
  right atrium of the heart via the inferior and
  superior vena cava
• The right atrium contracts, forcing blood through
  the tricuspid valve into the right ventricle.
• The right ventricle contracts, closing the
  tricuspid valve, and forcing blood through the
  pulmonary valve into the pulmonary arteries
• The pulmonary arteries carry deoxygenated blood
  to the lungs to release excess carbon dioxide
  (CO2) while red blood cells pick up a new supply
  of oxygen (O2)
• Freshly oxygenated blood returns to the left
  atrium of the heart via the pulmonary veins.
• The left atrium contracts, forcing blood through
  the bicuspid/mitral valve into the left
  ventricle.
• The left ventricle contracts, closing the
  bicuspid valve and forcing open the aortic valve
  . Blood enters the aorta to provide oxygenated
  blood to the entire body after a journey through
  the blood vessels!

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Cardiac Muscle Contraction

• Cardiac muscle contraction occurs in specific
  steps to ensure that blood is routed to the
  proper location.
• Contraction is caused by action potentials
  depolarizing the cardiac muscle cells leading to
  sarcomere shortening

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Remember

• Molecules do NOT like being crowded and will move
  to the LESS crowded side
• Depolarization Sodium (Na) IN
• Repolarization Potassium (K) OUT

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• Cardiac Muscle Calcium (Ca) goes into cardiac
  cells, prolonging depolarization, increasing
  force of contraction, and increasing amount of
  calcium available to initiate sarcomere
  shortening (SFT)

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Cardiac Muscle Anatomy

• Gap junctions _at_ intercalated discs allow for
  rapid movement of molecules (sodium, potassium,
  calcium) in and out of cell, and thus, quick
  action potentials and muscle contractions

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Cardiac Muscle Contraction

• Contraction starts at the Sinoatrial (SA) Node
  which contains specialized pacemaker cells. These
  cells can generate spontaneous action potentials
  without input from the nervous system.

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Pacemaker Potential

• Slow influx of Na into cardiac cells between
  action potentials
• Increases membrane potential positively toward
  threshold potential, allowing for autorhythmicity
  of cardiac cells at the SA node (all-or-none
  response).

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1. Sinoatrial (SA) node (Pacemaker)
2. Atrioventricular (AV)node
3. Bundle of His
4. Left Right Bundle branches
5. Purkinje Fibers

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Electrical Conduction System of the Heart

• SA NODE ? AV NODE ? BUNDLE OF HIS ? LEFT RIGHT
  BUNDLE BRANCHES ? PURKINJE FIBERS
• SA node 50 msec.
• The pacemaker.
• AV node 100 msec Atrial contraction occurs.
• AV delay Action potential travels more slowly
• This delay ensures the ventricles relax and
  receive blood from atrial contraction BEFORE the
  ventricles get the signal to contract and pump
  blood out.
• 25 msec
• Bundle of His signal travels down septum
• Right and left bundle branches depolarization
  splits signal between the right and left
  ventricles

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Electrical Conduction System of the Heart

• 4. Purkinje fibers 50 msec
• Widespread fibers conduct action potentials
  throughout left and right ventricles. Ventricular
  contraction begins.

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Impulse Conduction through the Heart
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Video Clip

• http//highered.mcgraw-hill.com/sites/0072495855/s
  tudent_view0/chapter22/animation__conducting_syste
  m_of_the_heart.html