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MODULE 4 TOPIC 1 LECTURE 3.docx - THE CARDIOVASCULAR SYSTEM...

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THE CARDIOVASCULAR SYSTEM IIPhysiology of theheart Intrinsic conductingsystemSinoatrial (SA)node – nameddue to location)oElectricalpacemakeroGenerates a pulse of approx. 75 beats/minoQuick depolariser - sets pace for sinus rhythm Atrioventricular (AV) node (beats slower)oReceives impulses from SA nodeoTriggers depolarisation further through the heart, this moves through the AV bundle Atrioventricular (AV) bundle (series of nerves)oBundle of HISoElectrical link between atria and ventricles (only direct link)Subendocardial conducting network (allow impulses to reach all over heart)oPurkinje fibresoDistribute impulses to ventriclesCardiac pacemaker cells Autorhythmic (ability of the heart to generate its own rhythm)Ability to spontaneously depolarise (don’t require stimulus – initially stimulated by nervous response, but then able to conduct independently without further stimulation)Contain special cell membrane ion channelsDistributed throughout intrinsic conducting systemFastest cells located in SA node (75-100bpm)SA node (strongest contraction) sets initial pace (pacemaker)Ectopic pacemaker (25-40bpm) – AV node can act as pacemaker temporarily as a fail-safe measure, but much slower
Sequence ofexcitation Matchessequence ofblood flowStart with SAnode, sends outexcitation signalmostly throughRAWhole of atriathen receivingthe signal and isdepolarised, thisexcites the AVnodeCausescontraction ofthe atria, atriabegin to repolarise, and the signal is sent down AV bundle toward apex of heartOnce whole of atria has returned to neutral, the cardiac signal is continuing up through the subendocardial network, causes depolarisation of the entire ventricular region, from APEX up, leading to ventricular contractionElectrocardiography(ECG) The electrical impulsesgenerated by the heartcan be measured(electrocardiogram –ECG/EKG)Doctors look for normalcirculatory functioning Tells us about differentsteps in thecontraction of theheart and the electricalsignalling that controlsitShows currents arising from electrical activity of the heartRecorded by electrodes placed on skinSize and shape varies dependent on electrode positionBasic features: P wave, QRS complex and T waveoP wave = atrial depolarisation (atrial contraction)oQRS complex = ventricular depolarisation (ventricular contraction)o

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Term
Three
Professor
Jacinta Hewitt
Tags
Blood vessel

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