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Heart: Length-tension relationships Starling’s law of the heart

Heart: Length-tension relationships Starling’s law of the heart reflex control of heart contraction Smooth muscle Anatomy Contraction mechanism Contraction regulation. Length-tension relationships. There is an optimal sarcomere length for generating a maximal force during contraction.

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Heart: Length-tension relationships Starling’s law of the heart

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  1. Heart: • Length-tension relationships • Starling’s law of the heart • reflex control of heart contraction • Smooth muscle • Anatomy • Contraction mechanism • Contraction regulation

  2. Length-tension relationships • There is an optimal sarcomere length for generating a maximal force during contraction. • As blood enters the ventricle, it expands and the sarcomere length increases • The stroke volume increases when the force of contraction increases

  3. Starling’s law of the heart • The relationship between stretch and force in the intact heart. • The force of contraction (stroke volume) is proportional to the end-diastolic volume. • Within physiological limits, the heart pumps all the blood that returns to it.

  4. Starling’s Law of the Heart

  5. Understand: • Integration of factors that regulate heart activity

  6. Smooth muscle • Blood vessels, G-I tract, urinary tract, reproductive tract,iris, etc. • Slow, sustained contraction • No sarcomeres • Yes, contractile filaments

  7. Example of smooth muscle • Sphinctors • Smooth muscle is tonically contracted • Sphinctor relaxes when material leaves a hollow organ (eg. Esophagus  stomach)

  8. Smooth muscle cells • Single nucleus • Actin and myosin are located diagonally around periphery and single nucleus

  9. Proteins associated with actin • Actin • Tropomyosin • Actin filaments attach to dense bodies of protein • Actin filaments terminate in protein plaques of cell membrane

  10. Myosin • Myosin thick filaments located between actin filaments • Myosin heads line thick filament surface • Slow ATPase activity • Myosin light chain kinase phosphorylates myosin head (activates ATPase, stimulating cross-bridge cycling)

  11. CaM is calmodulin MLCK is myosin light chain kinase

  12. Sometimes, • dephosphorylated • myosin remains • attached to actin • latch state, contraction • is maintained • Maintain contraction without ATP.

  13. Source of calcium • Pacemaker potentials • Depolarization through Ca++ entry • In single unit smooth muscle, gap junctions spread Ca++ • Ca++ induced Ca++ release • Myogenic contraction

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