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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