Intrinsic effects increased cross bridge formation

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Unformatted text preview: rtic & pulmonary insufficiency •  mitral & tricuspid stenosis –  Both •  patent ductus arteriosis •  combined valvular defect Aortic stenosis is much louder then mital insufficiency Law of Laplace •  Wall tension = (pressure)(radius)/2 •  At a given operating pressure as ventricular radius ⇑ , developed wall tension ⇑. –  ⇑ tension ⇒ ⇑ force of ventricular contraction –  two ventricles operating at the same pressure but with different chamber radii •  the larger chamber will have to generate more wall tension, consuming more energy & oxygen Terminology •  Chronotropic (+ increases) (- decreases) –  Anything that affects heart rate •  Dromotropic –  Anything that affects conduction velocity •  Inotropic –  Anything that affects strength of contraction •  eg. Caffeine would be a + chronotropic agent (increases heart rate) –  Batista resection •  How does this law explain how capillaries can withstand high intravascular pressure? 10 The amt of blood pumped each minute by the heart is determined by the amount of blood flow into the heart from the veins- Venous Return Frank-sterling mechanism of the heart: Intrinsic ability of the heart to adapt to increasing volumes of inflowing blood The greater the heart muscle is stretched during filling the greater the contraction and quantity of blood pumped to the aorta 110 110 Control of Heart Pumping •  Intrinsic properties of cardiac muscle cells •  Frank-Starling Law of the Heart –  Within physiologic limits the heart will pump all the blood that returns to it without allowing excessive damming of blood in veins •  heterometric & homeometric autoregulation •  direct stretch on the SA node Mechanism of FrankStarling •  Increased venous return causes increased stretch of cardiac muscle fibers. (Intrinsic effects) –  increased cross-bridge formation –  increased calcium influx •  both increases force of contraction –  increased stretch on SA node •  increases heart rate Stretching of the right atrial wall increases the heart rate by 10-20% Heterometric autoregulation •  Within limits as cardiac fibers are stretched the force of contraction is increased –  more cross bridge formation as actin overlap is removed –  more Ca++ influx into cell associated with the increased stretch Homeometric autoregulation •  Ability to increase strength of contraction independent of a length change –  Flow induced •  increased stroke volume maintained as EDV decreases –  Pressure induced •  increase in aortic BP (afterload) will + force of contraction –  Rate induced •  increased heart rate will + force treppe Direct Stretch on SA node •  Stretch on the SA node will increase Ca++ and/or Na+ permeability which will increase heart rate •  •  •  •  Extrinsic Influences Autonomic nervous system Hormonal influences Ionic influences Temperature influences 11 111 111 Control of Heart by ANS •  Sympathetic innervation–  + heart rate –  + strength of contraction –  + conduction velocity Interaction of ANS •  SNS effects on the heart blocked using propranolol (beta blocker) which blocks beta receptors •  Para effects blocked using atropine which blocks muscarinic receptors –  HR will increase –  Strength of contraction decreases •  Parasympathetic innervation –  - heart rate –  - strength of contraction –  - conduction velocity Parasympathetic stimulation works more on decreasing the heart rate then it does on decreasing the strength of contraction •  What can be concluded? That th e heart rate is being increased...
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