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Unformatted text preview: all of the right atria and from here the AP travels thru both atria to the AV bundle and into the ventricals. 7 Initiation in the atria allows it to pump blood into the ventrical before the strong vetricular contraction and the atria is therefore known as a primer pump AV node may act as the pace maker in the abscence of a fxning SA node Overdrive Suppression
• If you drive a self-excitatory cell at a rate faster than its own inherent rate, you will suppress the cell s own automaticity
– Mechanism may be due to increased activity of Na+/K+ pump creating more negative Er – Cells of the AV node and purkinje system are under overdrive suppression by the SA node AV node
• Delays the wave of depolarization from entering the ventricle
– allows the atria to contract slightly ahead of the ventricles (.1 sec delay) • Slow conduction velocity due to smaller diameter fibers • In absence of SA node, AV node may act as pacemaker but at a slower rate Heart fills with blood during diastole Effect of HR on systole/diastole
• As heart rate (HR) ↑ cycle length (CL) ↓ • At a resting heart rate systole (S) < diastole (D) • Both the duration of systole and diastole shorten, but diastole shortens to a greater extent
– At high HR the ventricle may not fill adequately P. 106 Cardiac Cycle
Isovolumic = valves are closed – isovolumic contraction – ejection Mitral are closed and aortic are open • HR of 75 BPM; CL = .8 sec. S = .3 D = .5 • HR of 150 BPM; CL = .4 sec. S = .2 D = .2 • During systole perfusion of the myocardium is restricted by the contracting cardiac muscle compressing blood vessels (especially in LV)
Cycle systole= contraction - ejection Diastole = relaxation
Coronary flow in left ventricle peaks at onset of diastole • Diastole Enters diastole phase after relaxation (contraction) – isovolumic relaxation – rapid inflow- 70-75% – diastasis – atrial systole- 25-30%
relaxation Mitral and tricusoid are open Aortic and pulmonary are closed during diastole phase Both valves are closed at both the onset of contraction and onset of 106 106 Onset of Ventricular Contraction
• Isovolumic contraction
– Tricuspid & Mitral valves close
• as ventricular pressure rises above atrial pressure Ejection of blood from ventricles
• Most of blood ejected in first 1/2 of phase • ventricular pressure peaks and starts to fall off • ejection is terminated by closure of the semilunar valves (pulmonic & aortic) – Pulmonic & Aortic valves open
• as ventricular pressure rises above pulmonic & aortic artery pressure During isovolumic contraction there is no emptying as pressure builds in the ventricals During isovolumic relaxation the intraventricular pressure decreases rapidly As pressure builds in the arteries the blood tries to get back into the ventricals but the aortic and pulmonary valves close quickly 8 Ventricular Relaxation
• Isovolumetric (isometric) relaxation-As the ventricular wall relaxes, ventricular pressure (P) falls; the aortic and pulmonic valves close as the ventricular P falls below aortic and pulmonic artery P • Rapid inflow-When ventricular P falls below atrial...
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This note was uploaded on 05/03/2011 for the course PHYS 339 taught by Professor Free during the Spring '11 term at Palmer Chiropractic.
- Spring '11