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Unformatted text preview: Circulatory Systems Pt 2 Physiology of Contraction Depolarization, plateau, repolarization Depolarization & Repolarization Depolarization  resting membrane potential = -90mv  excitation spreads through gap junctions  fast Na+ channels open rapid depolarization Plateau phase  250 msec  + Slow Ca channels open l Ca +2 enters from outside and from SR, while K + channels close  Ca +2 binds troponin allowing actin-myosin cross-bridge formation & tension development Repolarization  Ca +2 channels close and K + channels open & -90mv is restored Electrocardiogram---ECG or EKG Ion permeabilities EKG  Action potentials of all active cells P wave Na+  Atrial depolarization P to Q interval  conduction time (atrial to ventricular excitation); atrial contraction QRS complex Na+, K+  ; Ventricular depolarization atrial repolarization S-T segment Ca+  depolarization of contractile fibers (plateau phase); ventricular contraction T wave K+  Ventricular repolarization Q-T interval  Ventricular depolarization to repolarization Electrical and Mechanical Events in the Cardiac Cycle  Heart functions as an integrated organ  Electrical and mechanical events are correlated Changes in pressure and volume of chambers  Blood flow through chambers  Heart sounds  Opening and closing of valves Cardiac Output CO = HR x SV  Cardiac output (CO) = heart rate (HR) x stroke volume (SV)  Volume of blood pumped per unit time l Cardiac output can be modified by regulating heart rate and/or stroke volume  Heart rate  Modulated by autonomic nerves and adrenal medulla  Decreased HR (bradycardia)  Increased HR (tachycardia)  Stroke volume  Modulated by various nervous, hormonal, and physical factors Control of Stroke Volume (Fig 8.30)  Nervous and endocrine systems can cause the heart to contract more forcefully and pump more blood with each beat Regulation of Blood Flow  Arterioles control blood distribution l Because arterioles are arranged in parallel, they can alter blood flow to various organs  Vasoconstriction and vasodilation  Changes in resistance alter flow...
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This note was uploaded on 04/19/2008 for the course PCB 3713 taught by Professor Sikorski during the Spring '08 term at University of South Florida - Tampa.
- Spring '08