The Heart’s The Heart’s External Anatomy & External Anatomy & Conduction SystemConduction System

♥ Heart at restHeart at rest♥ Blood flows from large veins into atriaBlood flows from large veins into atria♥ Passive flow from atria into ventriclesPassive flow from atria into ventricles

♥ Atria (R & L) contract simultaneouslyAtria (R & L) contract simultaneously♥ Blood forced into ventriclesBlood forced into ventricles

♥ Ventricles (R & L) contract Ventricles (R & L) contract simultaneouslysimultaneously♥ Atrioventricular valves close Atrioventricular valves close “lubb” sound “lubb” sound♥ Blood forced into large arteriesBlood forced into large arteries

♥ Ventricles relaxVentricles relax♥ Semilunar valves close Semilunar valves close “dub” sound “dub” sound

♥ Heart at restHeart at rest

HEART

Pericardium

Pericardium♥Membrane sac

♥Surrounds the heart♥Protection♥Anchors♥Contains serous fluid

Pericarditis inflammation of the pericardium decreases serous fluid causing painful adhesions interfering with heart movements

Heart Wall

♥EpicardiumEpicardium (outside) – visceral layer (outside) – visceral layer of the serous pericardium.of the serous pericardium.

♥MyocardiumMyocardium (muscle) – cardiac (muscle) – cardiac muscle layer forming the bulk of the muscle layer forming the bulk of the heart.heart.

♥EndocardiumEndocardium (within) – endothelial (within) – endothelial layer of the inner myocardial surface.layer of the inner myocardial surface.

Cardiac Muscle♥Specialized muscle cellsSpecialized muscle cells

♥Involuntary Involuntary ♥Striated Striated ♥Cushioned by endomysiumCushioned by endomysium♥Joined by intercalated discsJoined by intercalated discs

♥Cardiac cell metabolismCardiac cell metabolism♥Areobic Areobic ♥Large mitochondria Large mitochondria ♥Organic fuels: fatty acids & glucoseOrganic fuels: fatty acids & glucose♥Fatigue resistanceFatigue resistance

♥ Left coronary arteryLeft coronary artery♥supplies left atrium and supplies left atrium and

left ventricleleft ventricle

♥ Anterior interventricular Anterior interventricular arteryartery

♥supplies both ventriclessupplies both ventricles

♥ Right coronary arteryRight coronary artery♥supplies right ventriclesupplies right ventricle

♥ Posterior interventricular Posterior interventricular arteryartery

♥supplies both ventriclessupplies both ventricles

Coronary ArteriesBranch off aorta above aortic semilunar valve

♥ Collects wastes from cardiac muscleCollects wastes from cardiac muscle

♥ Drains into a large sinus on posterior surface of Drains into a large sinus on posterior surface of heart called the coronary sinusheart called the coronary sinus

♥ Coronary sinus empties into right atriumCoronary sinus empties into right atrium

Coronary Veins

The heart beats because of the spread The heart beats because of the spread of electrical impulses to the heart of electrical impulses to the heart

muscle, causing it to contract.muscle, causing it to contract.

♥ Cardiac muscle tissue exhibits Cardiac muscle tissue exhibits autorhythmicityautorhythmicity = generates its own = generates its own stimulation. stimulation.

♥ This is possible because of an internal This is possible because of an internal cardiac conduction system which can cardiac conduction system which can initiate and distribute electrical impulses.initiate and distribute electrical impulses.

Cardiac Conduction System

♥Comprised of interconnected Comprised of interconnected structuresstructures♥ Sinoatrial nodeSinoatrial node♥ Atrioventricular nodeAtrioventricular node♥ Atrioventricular BundleAtrioventricular Bundle♥ Bundle BranchesBundle Branches♥ Purkinje Fibres Purkinje Fibres

Cardiac Conduction System

Sinoatrial (SA) Node

♥ Junction of atria and ventriclesJunction of atria and ventricles

♥ Spread of depolarisation - from atrial Spread of depolarisation - from atrial myocardiummyocardium

♥ Delay 0.15 secondsDelay 0.15 seconds♥ Time atria to expel bloodTime atria to expel blood

♥ Time for ventricular fillingTime for ventricular filling

♥ Protection to ventricles Protection to ventricles

♥ Less autonomic nervous control than SA nodeLess autonomic nervous control than SA node♥ Sympathetic ↑conduction timeSympathetic ↑conduction time

♥ Parasympathetic ↓conduction time Parasympathetic ↓conduction time

Atrioventricular (AV) Node

Atrioventricular node

Linked to the nervous system

♥ Depolarization begins Depolarization begins in sinoatrial (SA) nodein sinoatrial (SA) node

♥ Spread through atrial myocardiumSpread through atrial myocardium♥ Results in myocardial contration of the atriaResults in myocardial contration of the atria

♥ Delay in atrioventricular (AV) nodeDelay in atrioventricular (AV) node

♥ To the Bundle of His To the Bundle of His ♥ AKA atrioventricular bundleAKA atrioventricular bundle

DepolorizationThe heart is autorhythmicThe heart is autorhythmic

♥ Separates into 2 main Separates into 2 main branches left & rightbranches left & right♥ Located in the interventricular septumLocated in the interventricular septum

♥ Left bundle – antero-superior divisionLeft bundle – antero-superior division

♥ Right bundle – postero-inferior divisionRight bundle – postero-inferior division

♥ Bundle branches divide - small, dense network Bundle branches divide - small, dense network of conduction tissue called the of conduction tissue called the Purkinje FibersPurkinje Fibers

Entire musculature depolarizes quickly

DepolorizationThe heart is autorhythmicThe heart is autorhythmic

Variations in electrical potential radiate Variations in electrical potential radiate from the heart from the heart

ECG records electrical events in the heart. ECG records electrical events in the heart.

Electrocardiogram

P waveP waveDepolarization of atriaDepolarization of atriaFollowed by contraction Followed by contraction

QRS complexQRS complex3 waves (Q, R, & S)3 waves (Q, R, & S)Depolarization of ventriclesDepolarization of ventriclesFollowed by contractionFollowed by contraction

T waveT waveRepolarization of ventriclesRepolarization of ventricles

P-Q intervalP-Q intervalTime atria depolarize & remain Time atria depolarize & remain

depolarizeddepolarized

Q-T intervalQ-T intervalTime ventricles depolarize & remain Time ventricles depolarize & remain

depolarizeddepolarized

P-P = one cardiac cycleP-P = one cardiac cycleP-Q = time for atrial depolarizationP-Q = time for atrial depolarizationQ-T = time for ventricular Q-T = time for ventricular

depolarizationdepolarizationT-P = time for relaxationT-P = time for relaxation

SA node Represented on the ECG as P waveSA node Represented on the ECG as P wave

AV node conduction is represented on the AV node conduction is represented on the ECG as the PR Interval ECG as the PR Interval

The Bundle Branch and purkinje fibre depolarisation The Bundle Branch and purkinje fibre depolarisation constitutes ventricular depolarisation Represented constitutes ventricular depolarisation Represented on the ECG as the QRS on the ECG as the QRS

Atrial repolarisation occurs within the QRS & Atrial repolarisation occurs within the QRS & therefore is maskedtherefore is masked

Ventricular repolarisation is represented on the Ventricular repolarisation is represented on the ECG as a T waveECG as a T wave

P

PR

T

QRS

1) 1) atrialatrial depolarization beginsdepolarization begins2) atrial depolarization2) atrial depolarization complete complete (atria (atria contractedcontracted))

3) 3) ventriclesventricles begin tobegin to depolarizedepolarize at apex; at apex;atriaatria repolarize repolarize (atria (atria relaxedrelaxed))

4) ventricular 4) ventricular depolarizationdepolarization complete complete (ventricles contracted)(ventricles contracted)

5) 5) ventriclesventricles begin tobegin to repolarizerepolarize at apex at apex6) ventricular repolarization6) ventricular repolarization complete complete

(ventricles relaxed)(ventricles relaxed)