Ch 18 Cardiac Physiology
Ch 18 Cardiac Physiology
Heart Anatomy
* heart chambers
* R L atrium
* R L ventricle
* valves
* R atrioventricular valve = tricuspid
* L atrioventricular = bicuspid = mitral
* aortic semilunar valve
* pulmonary semilunar valve
* other
* interventricular septum
* interatrial septum
Heart Anatomy
* blood vessels
* SVC , IVC into R atrium
* pulmonary veins into L atrium
* pulmonary trunk out of R ventricle
* aorta out of L ventricle
cardiac muscle tissue
* striated (sarcomeres)
* short cells , branched
* intercalated discs specialized connections betw cells
* desmosomes prevents separation of cells
* gap junctions allow ions to pass betw cells
* functional syncytium all cells contract simultaneously
* many mitochondria aerobic respiration prevents fatigue
* autorhythmic contract w/o stim from nerves
cardiac vs skeletal muscle tissue
* cardiac muscle doesn’t fatigue
* long contraction
* long refractory period
* contraction
* skeletal muscle motor units
* cardiac muscle entire myocardium
* cardiac muscle cells can stimulate adjacent cells to contract
cardiac muscle contraction - 1
* contracts just like skeletal muscle :
* fast Na+ channels (voltage-gated) open
* Na+ rushes in
* depolarization ( -90mV to +30 mV)
* depolarization opens Sarcoplasmic reticulum
* Ca++ stimulates sarcomere to contract
* only different :
cardiac muscle contraction - 2
* plateau delayed repolarization
* depolarization opens slow Ca++ channels
* Ca++ moves in inside stays + much longer
* Na+ depol last 1-5 ms
* Ca++ depol lasts 150-200ms
* decreased K+ permeability
* repolarization delayed until after plateau
* repolarization
* K+ channels open
* Ca++ pumped out of cell or into SR
cardiac muscle contraction - 3
* much longer contraction in cardiac muscle
* long refractory period 250 ms vs skeletal 2-3ms
* prevents summation
* prevents fatigue
* prevents tetany
functional syncytium
* all cells contract simultaneously
* gap junctions + from adjacent cells
* cell stimulates adjacent cells
* intrinsic conduction system initiates impulses
instrinsic conduction system
* non-contractile cardiac cells
* act like neurons
* initiate and spread action potential for entire myocardium
* autorhythmic
autorhythmic cells
* unstable resting potential
* pacemaker potential spontaneous depolarization
* membrane potential -60 mV
* slow Na+ channel open Na+ leaks in
* threshold - 40 mV
* fast Ca++ channel open Ca++ rush in = depolarization
* repolarization K+ out (Na-K pump)
* rhythm of spontaneous depolarization
conduction pathway
* Sino-atrial (S-A) node
* Atrio-ventricular (A-V) node
* A-V bundle (bundle of His)
* bundle branches
* Purkinjie fibers
* gap junctions spread depolarization along pathway
S-A node
* sino-atrial node = pacemaker
* right atrium
* prepotential ~ 90+ / min
* fastest autorhythmic tissue
* sets pace for entire myocardium
* slowed by P-ANS ~ 70 – 75 / min
* sinus rhythm normal
A-V node
* atrio-ventricular node
* internodal pathway from S-A node
* atrium contracts
* delay ~ 0.1 msec
* 50 / min w/o S-A node
* atrioventricular bundle (bundle of His)
* “electrical” connection betw atrium and ventricle
* R & L bundle branches
* Purkinjie fibers
* bundle to Purkinjie = ventricular contraction
* plus gap junctions of myocardium
* contraction begins at apex and moves upward
ECG
* electrocardiogram
* ECG is record of all depolarizations of heart
* waves :
* P wave - atrial depolarization
* QRS complex - ventricular depolarization
* T wave - ventricular repolarization
* intervals :
* P-Q interval begin atrium to begin ventricle
* S-T segment ventricular plateau
* Q-T interval entire ventricular events
* R-R interval 1 beat heart rate
Arrhythmia
* irregular heart beat
* bradycardia slow rate < 60
* tachycardia fast rate > 100
* palpitation brief, temporary arrhythmia
* flutter fast, consistent heart rate > 200
* fibrillation fast, uncoordinated > 300 ventricles contract w/o filling
* PVC = premature ventricular contraction occassional, irreg. ventricular contraction cardiac muscle become conductive
* asystole no contractions
innervation of heart
* vital signs - what part of brain ?
* cardioaccelerator center
* S-ANS to S-A node and pathway - increase rate stronger contract
* cardioinhibitory center
* P-ANS to S-A node and A-V node - decrease rate weaker contract
* modify the rate of depolarization - doesn’t cause pacemaker potential
* epinephrine S-ANS , hormone
* stim ß adrenergic receptors
* cAMP mediated
* open Na channels
* depolarizes faster
* acetylcholine P-ANS
* open K channels
* depolarizes slower
Cardiac cycle
* 1 “heartbeat”
* all events of blood flow
* systole = contraction
* atrial systole
* ventricular systole
* diastole = relaxation
* atria and ventricles relax
* systole + diastole = cardiac cycle
cardiac cycle - basic
* atrial systole atria contract
* ventricular systole ventricles contract
* (atrial diastole)
* diastole all chambers relax
cardiac cycle - details
* ventricular filling
* passive filling atrium to ventricle
* atrial systole “
* ventricular systole
* isovolumetric contraction A-V valves close no blood movement yet
* ventricular ejection SL open ventricle to artery
* diastole
* isovolumetric relaxation SL valves close
Heart valves
* function : prevent backflow
* open and close by pressure of moving blood
* A-V valves
* open : weight of blood from atria
* close : pressure of ventricular contraction
* Semilunar valves
* open : pressure of ventricular contraction
* close : weight of blood in artery (aorta ; pulmonary )
Heart sounds
* closing of valves
* 1st = A-V valves close
* forces blood against valves
* ventricular systole
* 2nd = Semilunar valves close
* gravity from blood in arteries
* ventricular diastole
heart murmurs
* abnormal heart sounds abnormal blood flow
* defective valves
* mitral stenosis thickened mitral valve
* regurgitation fail to close
* septal defects
* interatrial
* patent ductus arteriosus
Cardiac output
* = amt. blood pumped / minute / ventricle
* Cardiac output = stroke volume x heart rate CO = SV x HR
* heart rate = pulse = beats / min
* stroke volume = amount pumped / beat / ventricle
* “resting stroke volume” ~ 70 ml/beat
* HR ~ 70 beat / min
* CO = 70ml x 70 beat/min = 4900 ml/min ~ 5 liters/ min
* stronger heart (( SV ) ( slower heart rate
* 100ml x 50 beat/min = 5000 ml\min
* weak heart requires ( HR (more work)
stroke volume
* EDV end diastolic volume after filling
* ESV end systolic volume after contraction
* SV = EDV - ESV
* SV = 120 ml - 50 ml = 70 ml
factors affecting EDV
* preload = venous return
* Starling’s law of the heart : increase stretch of cardiac wall ( increase force of contraction
* ( venous return ( ( contraction (SV)
* ( venous return slow HR ( BP exercise (skeletal muscle pump)
* ( venous return very fast HR blood loss
factors affecting ESV – extrinsic factors
* contractility affect Ca++ entry into cells
* positive inotropic agents S-ANS epinephrine thyroxine digitalis
* negative inotropic agents P-ANS K+ H+ (pH) Ca channel blockers beta blockers
* afterload backpressure from arteries (BP)
factors affecting HR
* chronotropic factors
* increase S-ANS epinephrine thyroxine
* decrease P-ANS vagal tone
* baroreceptors atrial wall
* ( stretch ANF ; S-ANS
* emotion ANS
cardiac disease
* MI myocardial infarction
* ischemia decreased blood supply
* infarct destroyed myocardium
* CAD coronary artery disease CABG
* CHF congestive heart failure
* MVP mitral valve prolapse
* Mitral stenosis decreased size of opening in valve
* Angina brief pain of coronary artery origin
* Rheumatic heart disease Strept infection
* arrhythmia
* Atherosclerosis decreased lumen due to plaques
*
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