Cardiovascular SystemStructure lies within thorax b/w lungs in the mediastinal space beating is palpable @ 5th intercostals space, approx 2 in. left of midline this pulsation (arising at the apex of the heart) is termed point of maximal impulse. Endocardium = thin, inner lining/layer Myocardium = layer of muscle Epicardium = fibrous, outer layer Heart is surrounded by the pericardiumo Inner (visceral) layer is in contact with the epicardiumo Outer (parietal) layer is connected with the mediastinum Pericardial fluid lubricates the space b/w the pericardial layers and prevents friction. Heart is divided vertica ...view middle of the document...
Conduction system Specialized nerve tissue responsible for creating and transporting the electrical impulse or action potential. Impulse initiates depolarization & cardiac contraction. Electrical impulse is initiated by SA (sinoatrial) note; the pacemaker of the heart. Mechanical contraction of the atria follows the depolatization Impulse travels from atria AV node bundle of Hisleft and right bundle branches The action potential diffuses widely through the walls of both ventricles by means of Purkinje fibers The efficient ventricular conduction system delivers the impulse within 0.12 seconds; this triggers a uniform ventricular contraction Cycle starts with depolarization of SA node Cycle ends with repolarization when the contractile fiber cells & conduction pathway cells repair their resting polarized conditionElectrocardiogram Detects electrical activity of heart P = firing of the SA node & represents depolarization of the fibers of the atria QRS = depolarization from the AV node through the ventricles NOTE - there is a delay of impulse transmission through the AV node that accounts for the time sequence between the end of the P wave and the beginning of the QRS wave. T = repolarization of the ventricles U = if seen, represents delayed ventricular repolarization & may be associated with hypokalemia. Intervals b/w these waves reflect the length of time it takes for the impulse to travel from one area of the heart to another.Mechanical System Systole = contraction of the myocardium; results in ejection of blood from the cardiac chamber Diastole = relaxation of the myocardium; allows for filling of the chamber. Cardiac output = measurement of mechanical efficiency; is the amount of blood pumped by each ventricle in 1 min. CO is calculated by multiplying stroke volume by heart rate. For the normal adult at rest, CO is 4-8 L/min. Cardiac index = the CO divided by the body mass index. Normal CI is 2.8-4.2 L/min per square meter.Factors affecting cardiac output Preload = determines the amnt. of stretch placed on myocardial fibers. Contractility can be increased by norepinephrine released by the sympathetic nervous system, as well as by epinephrine; this raises the SV by increasing ventricular emptying. Afterload = peripheral resistance against which the left ventricle must pump and is affected by the size of the ventricles, wall tension and arterial blood pressure; ventricular hypertrophy (enlargement of the cardiac muscle tissue without an increase in the size of the cavities).Cardiac Reserve The ability to respond to demands by altering CO threefold or fourfold is termed cardiac reserve Increase in Co results from increase in HR or SV HR can increase to as high as 180 bpm for short periods. The SV can be increased by increas...
