The Heart Chapt. 9 Heart Muscle; The Heart as a Pump and Function of - PowerPoint PPT Presentation

The Heart Chapt. 9 Heart Muscle; The Heart as a Pump and Function of the Heart Valve By: Dr. Foadoddini Department of Physiology & Pharmacology Birjand University of Medical Sciences ١ Dr. Foadoddini

٢ Dr. Foadoddini

Electrical Activity of the Heart • Ion channels: – They are selective – A given ion may have several different channel ٣ Dr. Foadoddini

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Excitation-contraction coupling ٧ Dr. Foadoddini

Electrical Activity of the Heart • Maintenance of Ionic Gradient: – Digitalis inhibit Na ‐ K pump – = 2×10 ‐ 3 and [Ca] i = 10 ‐ 7 [Ca] o – 10 ‐ 5 M – Na ‐ Ca Exchanger can operate in either direction (depend upon the membrane potential) – Decreased Na ‐ K ATPase activity increase intracellular Na and Ca ٨ ٨ Dr. Foadoddini

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Intercalated disck Functional Syncytium ١١ Dr. Foadoddini

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Electrical Activity of the Heart • In non-pacemaker cells Action potential: I to ↓ I K (Inward rectifier) ↑ I K (Delayed rectifier) The long ERP prevent the heart developing sustained, tetanic contraction These potentials are so called ‘ Fast Response’ action potential because of rapid phase 0 depolarization ١٤ ١٤ Dr. Foadoddini

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Cardiac valves One way path Passive opening/closing Diameter diffferences Cordae tendineae ١٦ Dr. Foadoddini

Volume-pressure curves as heart work Area under curve as cardiac external work ١٧ Dr. Foadoddini

Cardiac cycle Pressure ‐ volume relationship 1. ABC: Ventricular Diastole 2. CD: Isovolumic contraction. 3. DF: Ventricular Systole 4. DE: Ejection (Rapid and reduced ejection) 5. FA: Isovolumic relaxation 6. ABC: Filling phase (Rapid filling and diastases) Atrial systole ١٨ Dr. Foadoddini

CO End-diastolic pressure Venous return/Atrial pressure ١٩ Dr. Foadoddini

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Frank-Starling mechanism ٢١ Dr. Foadoddini

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Arterial pressure ٢٤ Dr. Foadoddini

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Chapt. 10 Rhythmical Excitation of the Heart ٢٦ Dr. Foadoddini

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Electrical Activity of the Heart • Action potential: In pacemaker cells ↑ I K (Delayed rectifier) – They are in SA and AV node – They do not have a true resting potential – Fast Na channels are in activated – They induces Overdrive suppression T-type Ca current •These potentials are so called ‘ Slow Response’ action potential because of slow phase 0 depolarization •Sometimes Fast Responses are converted to the Slow Responses ٢٩ Dr. Foadoddini

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Stokes-Aadams syndrome (after A-V block) ٣١ Dr. Foadoddini

Electrical Activity of the Heart Neuronal mechanisms that alter pace-maker activity Ventricular escape Normal range = 100 to 110 beats/min 60 beats/min to over 200 beats/min • At resting heart, vagal influences are dominant over sympathetic (vagal tone) • Change in heart rate = Chronotropy • Change in contraction = Inotropy • Change in conduction velocity = Dromotropy ٣٢ Dr. Foadoddini

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