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BIOL 1412 (89)
Lecture

BIOL1412 02 28 2014.docx

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School
University of Manitoba
Department
Biological Sciences
Course
BIOL 1412
Professor
Paul Messing
Semester
Winter

Description
BIOL1412 02 28 2014 Cardiac Physiology Excitation-Contraction coupling in Myocardial Cell: 3) Contraction (Fig. 18.13) - sliding filament mechanism - begins a few msec afterAP begins - Duration ofAP = ~250 msec - ∴ contraction almost over whenAP ends - Result = NO summation ∴ NO tetanus (Fig. 9.15) - get alternation of contraction/relax Final Exam -APRIL15th 2014 Cardiac Cycle 3 components: 1) ElectricalActivity (ECG) - small currents due to depol./repol. of heart move through salty body fluids - potential difference measured on body surface using electrodes ( = leads) - recording seen as waves (refer to PQRST graph on Laboratory #3) - = sum of electrical activity of all myocardial cells (not anAP) - ECG Waves: a) P wave = atrial depol. ⇒ followed by contraction (Fig. 18.18) b) QRS wave = ventricular (vent.) depol. ⇒ contraction - also atrial repol. (⇒ relaxation) - masked by larger vent. electrical event (larger muscle mass) c) T wave = ventricular repol. ⇒ followed by relaxation - ECG Intervals: (Fig. 18.17) a) P ⇒ Q = atria contracted, signals passing throughAV node b) S ⇒ T = ventricles contracted, atria relaxed c) T ⇒ P = heart at rest - Abnormalities of Heart Beat: a) Tachycardia = resting HR more than 100 bpm (beats per minute) b) Bradycardia = resting HR less than 60 bpm c) Heart Block = conduction throughAV node slowed, get ⇑ P⇒Q interval ⇒ vent. may not contract after each atrial contraction eg. 3rd degree heart block - no conduction throughAV node - atria fire at SAnode rate ( ~75APs/min.), vent. at Bundle/Perkinje rate ( ~30 APs/min.) 2) MechanicalActivity: - 2 main events: a) Systole = contraction, employing b) Diastole = relaxation, filling - both initiated by electrical activity (Fig. 18.17) - 1 complete heart beat = diastole + systole of atriaAND diastole + systole of ventricles (Fig. 18.5) - Timing of mechanical events: - average resting heart rate (HR) = 75 beats/min. - ∴ 0.8 sec/beat = 1 cardiac cycle (60 sec/min. / 75 beats/min.) (Fig. 18.21) 0.1 0.2 0.3 0.4 0.5 0.6 0
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