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Chapter 13 continued

Chapter 13 continued - Chapter 13 continued Begin Exam 3...

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Chapter 13 continued ________________________________________________________________________________ Begin Exam 3 Electrocardiogram – a prolonged QRS complex may result from damage to the AV bundle fibers Role of Hormones on Heart Epinephrine and Norepi Increased contractibility by increasing [Ca++] within the cardiac muscle fiber. Comparison to Skeletal & Smooth Muscles Properties similar to skeletal muscle T tubules Sarcoplasmic reticulum calcium storage Troponin-tropomysin regulation Properties similar to smooth muscle Gap junctions Extracellular calcium Look at the diff of excitation in skeletal muscle compared to cardiac in (Fig 13.13) What doesn’t this have? A neuron, no motor-end plates Recording the Electrical Activity of the Heart with an Electrocardiogram Non-invasive technique Used to test for clinical abnormalities in conduction of electrical activity in the heart Body = conductor Currents in body can spread to surface (ECG, EMG, EEG) Standard ECG Trace (13.15b-know how to read) P wave: atrial depolarization QRS complex: ventricular depolarization T wave: ventricular repolarization PQ segment: AV nodal delay QT segment: ventricular systole TQ interval: ventricular diastole (only time the heart rests) ECG and Ventricular Action Potential (Fig 13.15) ** (a) Ventricular action potential recorded from a single contractile cell in the ventrical (single cell) (b) ECG surface recording of the summed electrical activity of all cells (all act as a whole) Arrhythmias Detected on ECG Arrhythmias: Abnormal heart rhythms. Flutter: extremely rapid rates of excitation and contraction of atria or ventricles. Just happens sometimes. Not usually a problem. Fibrillation: major problem Contractions of different groups of myocardial cells occur at different times Coordination of pumping impossible 1
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(Can’t pump the blood out of the heart, not good) Abnormal Heart Rates (Fig 13.16) “Sinus rhythm” = rhythm generated by SA node Abnormal Heart Rates: Ventricular fibrillation – rapid, uncoordinated depolarization of ventricles. Tachycardia - fast Bradycardia - slow (heart rate slows when your face is under water because you body thinks that you are drowning. It slows to conserve oxygen) Extrasystole: Extra contraction (Fig 13.16) PAC = premature atrial contraction PVC = premature ventricular contraction Ischemia Blood supply to the heart is stopped (Fig 13.31). something has blocked coronary arteries Cells become O 2 starved Can’t make ATP to pump Ca ++ out of the cytoplasm Produce lactic acid (H + ) ↑ in H + & Ca ++ close gap junctions in damaged cells isolating them Large areas of ischemia heart attack When myocardial cells die, they release enzymes which serve as markers Heart attacks do not have the same symptoms in women as in men.
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