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37 Cards in this Set
- Front
- Back
list the components of the myocardial cell
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1) myofibrils - provide the contractile elements, surrounded by:
2) the sarcolemma- a complex cell membrane which invaginates and forms: 3) T-tubules - network of tubules that carries electrical signals to the interior of the cell (opening of Ca++ channels) 4) sarcoplasmic reticulum- releases Ca++ to initiate contraction and uptake of Ca++ for relaxation 5) mitochondria- adjacent to myofibrils (more numerous than in skeletal muscle) |
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what is the myocardial contractile unit?
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sarcomere
Z line to Z line, 1.9 to 2.3 microns in length composed of actin and myosin |
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describe actin
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thin filament, contains reg. proteins (troponin/tropomyosin)
attach to Z lines |
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describe myosin
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thick filaments
provide ATPase activity for contraction |
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titin
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myofibrilar protein, provides elasticity and supports myosin
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which direction are subendocardial and subepicardial muscle fibers oriented?
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longitudinally
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which direction are the mid wall fibers oriented
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circumferential, perpendicular to the long axis
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describe the geometry of the left ventricle
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thick walled, prolate ellipsoid
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what are the mechanical properties of the ventricular chamber described in?
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pressure and volume (similar to force-length properties of skeletal muscle)
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what are the determinants of contraction?
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1.intracellular calcium levels
2.neurohumoral stimuli control signals 3. SR regulation of Ca++ uptake and release in response to stimuli |
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what are the 4 phases of diastole
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1.IVR- ACTIVE process
2.Early diastolic filling 3.Diastasis 4.Atrial Systole |
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does HR have a greater impact on diastole or systole?
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diastole
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what factors influence diastole?
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1. myocardial relaxation
2. ventricular filling 3. AV pressure gradient 4. passive elastic properties of the ventricle 5. HEART RATE |
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is diastolic dysfunction characterized by an increase of decrease in diastolic filling pressure?
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INCREASE (exacerbated by elevated HR)
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which kind of disorders is diastolic dysfunction common?
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those causing ventricular hypertrophy
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what are the determinents of IVR?
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1. maximal systolic pressure
2. end-systolic fiber stretch 3. coronary blood flow 4. elastic recoil |
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how is increased diastolic pressure manifested clinically?
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dyspnea
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is tau increased or decreased with delayed ventricular relaxation?
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increased
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when is relaxation complete with regards to the time constant tau
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3.5 times tau after aortic valve closure
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what is tau?
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a time constant used to assess ventricular relaxation
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which direction is the diastolic pressure-volume curve shifted in a stiffer, non compliant ventricle?
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to the LEFT
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when does this occur most often?
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situations of ventricular overload and hypertrophy (i.e. hypertension or AS)
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what is pre-load
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force acting to stretch a resting muscle
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how is pre-load definied in the ventricle?
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as end diastolic wall stress, the force at the maximal resting length of the sarcomere
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which CV indices are used to measure wall stress in vivo?
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end diastolic pressue/ end diastolic volume
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what is starling's law?
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force of contraction is dependent upon initial length of the sarcomere (and therefore extent of overlap between actin and myosin filaments-number of cross bridges that can form)
optimal overlap in cardiac muscle is 2.0 to 2.2 microns |
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for ventricular geometry, how is wall stress distributed?
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two ways:
1. Meridonial stress 2. circumferential stress |
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define meridonial stress
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F acting along the long axis of the ventricle and opposing long axis shortening
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define circumferential stress
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F acting along the equitorial direction and opposing circumferential fiber shortening
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define afterload
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F applied to myocardium in systole (for L ventricle it is the aortic P against which it pumps blood)
- influences extent of muscle shortening |
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how can afterload be defined?
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as systolic wall stress
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what are the two major components of afterload?
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aortic systolic pressure and aortic (arterial compliance)
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(T/F) Afterload and shortening are directly related
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False they are inversely related. An increase in AL will result in decreased shortening of the muscle fibers.
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define contractility (aka inotropism)
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instrinsic property of cardiac muscle to develop force at a given muscle length that determines the force and rate of contraction INDEPENDENTLY of afterload and preload
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what ion is contractility related to?
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Ca++ and it's interaction with contractile proteins.
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how is inotropism modulated
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neurohumoral factors and the adrenergic nervous system
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what is afterload mismatch?
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when compensatory mechanisms can no longer normalize wall stress and contractile performance declines leading to decreased contractility, myocyte death and ventricular failure
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