Cardiovascular Structure and Function

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Cardiovascular Structure and Function
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Function of CV system

• Transport of O2 to tissues and remove waste
  (delivery and garbage)
• Transport nutrients to tissues
• Regulate body temperature
• Right and left sides have separate functions

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R side

• Atria receives blood from systemic circulation
  (superior and inferior vena cavas)
• Ventricle pumps blood to lungs for oxygenation
  via pulmonary artery

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L side

• Receive blood (oxygenated) from lungs
• Pump blood into the aorta (thick-walled and
  muscular in nature) to systemic circulation

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4 chambered muscular organ

• 2 pumps, pulmonary and systemic circulation
• Heart muscle is called myocardium
• Striated, with actin and myosin filaments,
  similar to skeletal muscle
• Difference, cells are single nucleated,
  interconnected in a form similar to a lattice

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• Connected by intercalated disks that allows
  chemical and electrical coupling between cells
• Thick septum (interventricular septum) that
  separates R and L sides

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Cardiac Chambers

• Atria are thin walled, sac-like chambers, low
  pressure
• function is to receive and store blood while
  ventricles are contracting, act as primer pumps
• reservoir is more important than pump for blood
  propulsion

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• Ventricles are a continuum of muscle fibers
• contract from apex to base
• R ventricle is thicker than R atria
• L ventricle is 3X thicker than the R ventricular
  walls
• L ventricle can develop 4-5X more pressure than
  the R ventricle

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Number of valves in heart

• Thin flaps of endothelium covered fibrous tissue
• Movement of the valve leaflets are essentially
  passive
• Orientation of valves is responsible for the
  unidirectional flow of blood through the heart

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• Atrioventricular valves prevent backflow of blood
  from the ventricles into the atria
• also called tricuspid valve (three flaps or
  cusps) and mitral (bicuspid two flaps or cusps)
  valve
• Between right ventricle and pulmonary artery is a
  semilunar valve (three cusps) also called
  pulmonic valve
• Between left ventricle and aorta are semilunar
  valve (prevents backflow of blood from aorta into
  the heart)

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Blood flow through the heart

• 1. blood flows into right atrium from superior
  and inferior vena cava
• 2. blood travels from R atrium into R ventricle
• 3. blood flows through pulmonary artery into the
  lungs (for oxygenation)
• 4. blood returns from the lungs through the
  pulmonary veins, and is deposited into L atrium

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• 5. from L atrium, blood flows into L ventricle
• 6. blood leaves L ventricle via aorta, enters
  general systemic circulation

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Flow of electricity through the heart

• Heart has intrinsic rhythmicity
• 1. originates in SA (sino-atrial) node, superior,
  lateral aspect of R atrium
• 2. travels through both atria to AV node
  (atrioventricular), this causes depolarization of
  atria

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• 3. from AV node, pause for 0.01 sec, flows
  through AV bundle (aka bundle of His), through R
  and L bundle branches (RBB, LBB)
• this pause allows time for atrial contraction,
  pumping the last 20-25 of blood into ventricles

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• 4. from RBB and LBB, signal travels to the
  purkinje fibers in ventricles, which passes the
  current of depolarization to the ventricle muscle
• ventricles have a powerful contraction, and
  provide the major impetus to move blood
  throughout the CV system

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Action Potentials in cardiac muscle

• resting membrane potential of normal cardiac
  muscle is -85 to -95 millivolts
• specialized conductive fibers, purkinje, have a
  resting membrane potential of -90 to -100 mV
• action potential (AP) has a magnitude of 105 mV

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• this rise is 20 mV greater than needed, called
  the overshoot potential
• after depolarization, remains depolarized for 0.2
  sec in atrial muscle and 0.3 sec in ventricular
  muscle, which gives it the plateau
• plateau is followed by abrupt repolarization
• this plateau causes a contraction to last 3-15
  times longer than a skeletal muscle twitch

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Differenced in cardiac and skeletal muscle
membranes

• Action potential is caused by the opening of two
  types of channels a) fast sodium channels allow
  the sodium ions to enter the cell and b) slow
  calcium channel are slower to open and remain
  open longer (can be several tenths of a second
  sodium can also pass through these channels)

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• The permeability of cardiac muscle membrane to
  potassium decreases about 5X
• This decreases the outflux of K during plateau,
  preventing early recovery
• When Na and Ca channels close, influx stops,
  permeability for K increases rapidly
• Rapid influx of K, membrane potential returns to
  resting