The Cardiovascular System. The Heart. Chapter 20. Location. The heart lies in the mediastinum. Pericardium and Layers of Heart Wall. Chambers and Sulci. Chambers and Sulci. Right Atrium. Right Ventricle. Left Atrium. Left Ventricle. Anterior Heart. Myocardial Thickness and Function.
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The heart lies in the mediastinum.
Thickness of myocardium varies according to the function of the chamber
Autorhythmic cells – self excitable
Reduced permeability of K+, but no change in permeability to Na+.
Na+ continues to diffuse in.
Unstable resting potential – continuously depolarizes, drifting slowly toward threshold. (pacemaker potential)
Potentials initiated by conducting fibers stimulate contractile fibers.
Normal heart rate: 60-100 beats/min
Avg. heart beat at rest: 70-72 beats/min
Sinus tachycardia: > 100 beats/min
Sinus bradycardia: < 60 beats/min
Arrhythmias: abnormal rhythm resulting from a defect in the heart conduction system.
Fibrillation: rapid and irregular contractions. Can be atrial or ventricular.
Defibrillation: electrical shock to depolarize myocardium.
Ectopic Focus: a region of the heart, other than the conducting system, that causes and abnormal depolarization.
Junctional rhythm: AV node becomes pacemaker
Heart block: an arrhythmiathat occurs when electrical pathway between the atria and ventricle is blocked.
Lubb - AV valves close Dupp - semilunar valves close
Volume of blood pumped out by a ventricle with each beat
Stroke volume = end diastolic volume - end systolic volume
SV = EDV - ESV
EDV = Amount of blood that collects in a ventricle during diastole
ESV = Amount of blood remaining in a ventricle after contraction
SV depends on amount of stretch produced by venous return.
Averages about 70 ml/beat
Anything that influences heart rate or blood volume influences venous return and therefore SV
amount of blood pumped by each ventricle in one minute
Cardiac output = Heart rate x Stroke volume
CO = HR x SV
HR = beats per minute
SV = volume of blood pumped out by a ventricle with each beat
1. Autonomic regulation
2. Chemical regulation
3. Other Factors
Change stroke volume and/or heart rate
Congestive heart failure - occurs when the pumping ability of the heart is inadequate to provide normal circulation to meet body needs.
Pulmonary congestion - left side failure
Peripheral congestion - right side failure