The Heart. The heart is afist size pump that drives the blood in the arteries and veins throughout...

The HeartThe Heart

The HeartThe Heart

The heart is afist size pump that drives the blood in the The heart is afist size pump that drives the blood in the arteries and veins throughout the bodyarteries and veins throughout the body

It is somewhat conical in shapeIt is somewhat conical in shape

Its “base” lies upward and posteriorly, is made largely by the Its “base” lies upward and posteriorly, is made largely by the atria atria

Its “apex” is made by the tip of the left ventricle Its “apex” is made by the tip of the left ventricle

It rests on the central tendon of the diaphragmIt rests on the central tendon of the diaphragm

It is kept in its place by its pericardial attachments and the It is kept in its place by its pericardial attachments and the great vessels that enter into and emanate from its great vessels that enter into and emanate from its chamberschambers

It weighs about 300 gramsIt weighs about 300 grams

Location and general anatomy of the heart

Moore & Dalley Clinically Oriented Anatomy fifth edition LIPPINCOTT Williams & Wilkins

The HeartThe Heart

The heart is made of three layersThe heart is made of three layers

PericrdiumPericrdium

Fibrous outermostFibrous outermost

Parietal, adherent to the fibrous layerParietal, adherent to the fibrous layer

Epicardium (visceral), envelops the muscle layer and adherent to itEpicardium (visceral), envelops the muscle layer and adherent to it

Accumulation of blood or fluid in the pericardial sac can restrictAccumulation of blood or fluid in the pericardial sac can restrict

cardiac filling and subsequently cardiac output (cardiac cardiac filling and subsequently cardiac output (cardiac tamponade)tamponade)

MyocardiumMyocardium

The contractile layer responsible for the pumping actionThe contractile layer responsible for the pumping action

EndocardiumEndocardium

The inner lining of the cavities, extends to form the “valves”The inner lining of the cavities, extends to form the “valves”

A fibrous skeleton separates the atria from the ventricles and A fibrous skeleton separates the atria from the ventricles and provides provides

attachment to the cardiac muscleattachment to the cardiac muscle

Pathophysiology by McCance, fifth edition, Elsevier Mosby

Structure of the wall of the heart

Frank Netter, M.D., The CIBA Collection Vol V

The pericardium and the great vessels

The HeartThe Heart

The PericardiumThe Pericardium

It functions as a protecting layer around the heartIt functions as a protecting layer around the heart

It contains a minimal amount of serous fluid that facilitates It contains a minimal amount of serous fluid that facilitates

and lubricates the cardiac contractionand lubricates the cardiac contraction

It helps anchoring the heart in placeIt helps anchoring the heart in place

It prevents the sudden distension of the heart chambersIt prevents the sudden distension of the heart chambers

The HeartThe Heart

Gross Anatomy and FunctionGross Anatomy and Function

Two large veins collect the blood (venous return) from the body and pour Two large veins collect the blood (venous return) from the body and pour

it into the right atrium (RA)it into the right atrium (RA)

The superior vena cava (SVC) drains the blood from the head and neckThe superior vena cava (SVC) drains the blood from the head and neck

The inferior vena cava (IVC) collects the blood from the rest of the bodyThe inferior vena cava (IVC) collects the blood from the rest of the body

The RV pumps the blood to the lungs for gas exchangeThe RV pumps the blood to the lungs for gas exchange

Each lung sends its oxygenated blood to the left atrium (LA) through a Each lung sends its oxygenated blood to the left atrium (LA) through a pair pair

of pulmonary veins (a total of 4)of pulmonary veins (a total of 4)

There are no valves between the left atrium and the pulmonary capillariesThere are no valves between the left atrium and the pulmonary capillaries

Therefore pulmonary capillary pressure reflects left atrial pressureTherefore pulmonary capillary pressure reflects left atrial pressure

The LA sends the blood to the LV, and the LV pumps it into the rest od The LA sends the blood to the LV, and the LV pumps it into the rest od the the

body through the aortabody through the aorta

The HeartThe Heart


The heart is made up of four cavities (chambers)The heart is made up of four cavities (chambers)Two small chambers: right atrium (RA) and left atrium (LA), lie posteriorTwo small chambers: right atrium (RA) and left atrium (LA), lie posterior and superior to two larger ones, the ventriclesand superior to two larger ones, the ventriclesThe two atria are separated by a dividing interatrial “septum” (IAS)The two atria are separated by a dividing interatrial “septum” (IAS) Each atrium has an ear like appendage (auricle) that protrudes toward Each atrium has an ear like appendage (auricle) that protrudes toward

the corresponding great vesselthe corresponding great vesselThe atria form the “base” of the heartThe atria form the “base” of the heartThe atria are “receiving” chambersThe atria are “receiving” chambersThe ventricles are the pumping chambersThe ventricles are the pumping chambersThe atria normally contribute about 15% - 20% of the cardiac outputThe atria normally contribute about 15% - 20% of the cardiac output

The HeartThe Heart


Two large chambers: right and left ventricles (RV & LV) are separated by Two large chambers: right and left ventricles (RV & LV) are separated by an interventricular septum (IVS)an interventricular septum (IVS)

The ventricles lie below the atriaThe ventricles lie below the atriaThe tip of the left ventricle forms the “apex” of the heartThe tip of the left ventricle forms the “apex” of the heartThe ventricles are pumping chambers, therefore they are thicker walled The ventricles are pumping chambers, therefore they are thicker walled The left ventricle is thicker than the rightThe left ventricle is thicker than the rightThe right atrium and ventricle are separated by an endocardial reflection,The right atrium and ventricle are separated by an endocardial reflection, a “valve”, made of three leaf like structures, the tricuspid valve (TV)a “valve”, made of three leaf like structures, the tricuspid valve (TV)The left atrium and ventricle are separated by a valve made of two The left atrium and ventricle are separated by a valve made of two

leaflets, the mitral valve (MV)leaflets, the mitral valve (MV)The AV valves are made of “leaflets” while the pulmonary and aortic The AV valves are made of “leaflets” while the pulmonary and aortic

valvesvalves are made of “cusps”are made of “cusps”All the valves are attached to the cardiac skeletonAll the valves are attached to the cardiac skeleton


The right atrium


The cardiac chambers


The left atrium and ventricle


The heart valves during diastole (A) and systole (B)

Marieb Human Anatomy & Physiology seventh edition Pearson benjaamin Cummings

The general arrangement of the cardiac muscle

The HeartThe Heart

The CirculationThe Circulation

Blood is collected by the SVC and IVC and delivered to the RABlood is collected by the SVC and IVC and delivered to the RA

The RA sends the blood through the TV to the RVThe RA sends the blood through the TV to the RV

The RV pumps the blood through the PV and the PA to the lungsThe RV pumps the blood through the PV and the PA to the lungs

Gas exchange takes place in the lungsGas exchange takes place in the lungs

The lungs send the oxygenated blood to the LA through 4 The lungs send the oxygenated blood to the LA through 4 pulmonarypulmonary

veins, two for each lungveins, two for each lung

The LA delivers the blood through the MV to the LVThe LA delivers the blood through the MV to the LV

The LV pumps the blood through the AV into the AO to the rest The LV pumps the blood through the AV into the AO to the rest of the body, including the heart muscleof the body, including the heart muscle

The HeartThe Heart


The right ventricle pumps the blood to the lungs through the The right ventricle pumps the blood to the lungs through the pulmonary artery (PA)pulmonary artery (PA)

A valve at the root of the pulmonary artery, the pulmomary valve A valve at the root of the pulmonary artery, the pulmomary valve (PV)(PV)

prevents the blood from dropping back (regurgitating) into the prevents the blood from dropping back (regurgitating) into the

ventricleventricle

The left ventricle pumps its blood to the rest of the body through theThe left ventricle pumps its blood to the rest of the body through the

aorta (AO)aorta (AO)

A valve at the root of the aorta, the aortic valve (AV) prevents A valve at the root of the aorta, the aortic valve (AV) prevents

regurgitation back into the left ventricle regurgitation back into the left ventricle

Vander Physiology eighth edition McGraw Hill

Pulmonary and systemic circulation

The HeartThe Heart


Myocardial contraction is called “systole”Myocardial contraction is called “systole”

After each contraction the chambers relax “diastole”After each contraction the chambers relax “diastole”

The atria contract and relax together and the ventricles do the The atria contract and relax together and the ventricles do the samesame

At the time the atria contract the ventricles relax and vice versaAt the time the atria contract the ventricles relax and vice versa

Atrial systole propels the blood from the atria to the ventriclesAtrial systole propels the blood from the atria to the ventricles

The atria then relax (go in ”diastole”) and the ventricles go into The atria then relax (go in ”diastole”) and the ventricles go into systole sending the blood to the PA and the AOsystole sending the blood to the PA and the AO

Regurgitation of blood from ventricles to atria is prevented by the Regurgitation of blood from ventricles to atria is prevented by the TV andTV and

the MVthe MV

Systole

Diastole

The cardiac cycle


The HeartThe Heart


The right ventricle can cope with volume sending it a short The right ventricle can cope with volume sending it a short distancedistance

The left ventricle copes better with pressure sending the blood The left ventricle copes better with pressure sending the blood to the to the

rest of the bodyrest of the body

The HeartThe Heart


TV and MV competence is maintained by cord like structures TV and MV competence is maintained by cord like structures (chordae tendineae)(chordae tendineae)

These cords are attached on one side to the ventricalar surface These cords are attached on one side to the ventricalar surface of the valve, and to the other side to the tips of nipple like of the valve, and to the other side to the tips of nipple like protrusionsprotrusions

of the ventricaluar myocardiuml (papillary muscles) of the ventricaluar myocardiuml (papillary muscles)

Papillary muscles contract during systole preventing the Papillary muscles contract during systole preventing the prolapse of the AV valves into the atriaprolapse of the AV valves into the atria

The HeartThe Heart


Atrial systole helps to propel the blood from the atria but is not Atrial systole helps to propel the blood from the atria but is not essential essential

for the adequate output of blood from the ventriclesfor the adequate output of blood from the ventricles

Atrial systole contributes about 20% of the cardiac output (CO)Atrial systole contributes about 20% of the cardiac output (CO)

This contribution becomes important in cases of heart failureThis contribution becomes important in cases of heart failure

The terms systole and diastole, when used without chamber The terms systole and diastole, when used without chamber designation, indicate ventricular contraction and relaxationdesignation, indicate ventricular contraction and relaxation

The HeartThe Heart


The aortic and pulmonic valves are of the semilunar typesThe aortic and pulmonic valves are of the semilunar typesAortic and pulmonic valve closure is affected by the fall of the bloodAortic and pulmonic valve closure is affected by the fall of the blood column in the corresponding vessel during early diastolecolumn in the corresponding vessel during early diastoleThis downward pressure forces the three components (cusps) of This downward pressure forces the three components (cusps) of the valve to coapt preventing regurgitation into the ventriclesthe valve to coapt preventing regurgitation into the ventriclesVentricles do not eject all the blood they accumulate during diastole,Ventricles do not eject all the blood they accumulate during diastole, the end diastolic volume (EDV)the end diastolic volume (EDV) The difference between EDV and the volume ejected during systole,The difference between EDV and the volume ejected during systole, the end systolic volume (ESV) is the “stroke volume” (SV)the end systolic volume (ESV) is the “stroke volume” (SV) Therefore SV = EDV – ESVTherefore SV = EDV – ESVThe ratio SV/EDV is normally about 60%The ratio SV/EDV is normally about 60% This is referred to as the “ejection fraction” (EF)This is referred to as the “ejection fraction” (EF)

The HeartThe Heart

The MyocardiumThe Myocardium

The cardiac muscle is striated, shorter and thicker than the The cardiac muscle is striated, shorter and thicker than the skeletal muscleskeletal muscle

Cardiac cells branch and are interlock at “intercalated discs”Cardiac cells branch and are interlock at “intercalated discs”

Each cell has pale central nucleus and large mitochondriaEach cell has pale central nucleus and large mitochondria

Loose connective tissue surrounds the muscle, it carries the Loose connective tissue surrounds the muscle, it carries the blood supply and connects them to the fibrous skeleton that blood supply and connects them to the fibrous skeleton that anchors the muscleanchors the muscle

Dense bodies “desmosomes” in the intercalated discs hold the Dense bodies “desmosomes” in the intercalated discs hold the cells together during contractioncells together during contraction

Gap junctions exist between cells to allow the passage of ions Gap junctions exist between cells to allow the passage of ions and the action potential and the action potential

Cardiac muscle contracts and relaxes as a unit Cardiac muscle contracts and relaxes as a unit

Structure of the cardiac muscle


The HeartThe Heart

The MyocardiumThe MyocardiumThe contractile element of the muscle are fibres arranged in The contractile element of the muscle are fibres arranged in

filamentsfilaments

They are of two typesThey are of two types

Thick fibres “myosin”Thick fibres “myosin”

Thin fibers “actin”Thin fibers “actin”

The two types overlap longitudinallyThe two types overlap longitudinally

A bundle of filaments forms a “sarcomere”A bundle of filaments forms a “sarcomere”

The filaments are covered with cell membrane “sarcolemma”The filaments are covered with cell membrane “sarcolemma”

The myocardium exhibit “banding” : Z, A, M, and I bandsThe myocardium exhibit “banding” : Z, A, M, and I bands

Sarcomeres are surrounded by a network of channels, the Sarcomeres are surrounded by a network of channels, the sarcoplasmic reticulumsarcoplasmic reticulum

Sarcoplasmic reticulm is attached to invaginations of the Sarcoplasmic reticulm is attached to invaginations of the sarcolemma (T tubes) that allow the transfer of Casarcolemma (T tubes) that allow the transfer of Ca++++ to the fibrils to the fibrils

Frank Netter, M.D. The CIBA Collection V

The structure of the myocardium

The HeartThe Heart

The MyocardiumThe Myocardium

Myosin filaments lie in the middle between Z bandsMyosin filaments lie in the middle between Z bandsActin filaments are made of Actin filaments are made of Actin unitsActin units Troponin Troponin TropomyosinTropomyosin Each myosin fiber is attached to several troponin molecules on every one of theEach myosin fiber is attached to several troponin molecules on every one of the actin fibersactin fibersCaCa++++ unblocks actin/myosin binding sites, myosin attaches to tropomyosin unblocks actin/myosin binding sites, myosin attaches to tropomyosinMyosin head tilts pulling the Z lines closerMyosin head tilts pulling the Z lines closer

Each wave of depolarization is followed by an absolute refractory period during Each wave of depolarization is followed by an absolute refractory period during which no depolarization can take placewhich no depolarization can take place

The refractory period is equal to the length of cardiac muscle contractionThe refractory period is equal to the length of cardiac muscle contraction This guards against tetanic contraction of the cardiac muscleThis guards against tetanic contraction of the cardiac muscle

Davidson’s Principles and Practice of Medicine eighteenth edition Churchill Livingstone

Myosin actin interaction, myocyte shortening

Following actin/myosin interaction, Ca++ uptake pumps remove

Ca++ from the sarcoplasm back into the sarcoplasmic reticulum


Mechanism of muscle contraction


Cardiac muscle contraction

Myosin head resting ATP binds and transfers energy

Ca++ flux binds to tropnin shiftng tropomysin

Troponin

Tropomysin

Myosin cross bridge binds to binding site on thin filament, ADP moves away

ATP

Energy stored from (A) allows myosin head to move back to original position

The HeartThe Heart

The Coronary CirculationThe Coronary Circulation

The heart muscle gets its arterial supply from two main arteries that The heart muscle gets its arterial supply from two main arteries that

arise from the base of the aortaarise from the base of the aorta

The left main coronary artery divides into The left main coronary artery divides into

Anterior descending, runs along the IVS to the apex of the LV, andAnterior descending, runs along the IVS to the apex of the LV, and

Circumflex, turns around the LV and supplies its lateral wall and the Circumflex, turns around the LV and supplies its lateral wall and the LALA

The right coronary descends inferiorly, supplies the RV, SA nodeThe right coronary descends inferiorly, supplies the RV, SA node

It divides into twoIt divides into two

Marginal arteriy runs along the inferior border of the RV, andMarginal arteriy runs along the inferior border of the RV, and

Posterior interventricular artrey that supplies the IVS and Posterior interventricular artrey that supplies the IVS and anastomosesanastomoses

with the anterior descending at the apex with the anterior descending at the apex

The HeartThe Heart

The Coronary CirculationThe Coronary Circulation

Three cardiac veins form on the epicardiumThree cardiac veins form on the epicardium

The great cardiac vein along the anterior descending arteryThe great cardiac vein along the anterior descending artery

The middle cardiac vein along the posterior descending arteryThe middle cardiac vein along the posterior descending artery

The small cardiac vein along the marginal branch of the RCAThe small cardiac vein along the marginal branch of the RCA

All major three veins drain in the coronary sinus which opens in All major three veins drain in the coronary sinus which opens in the RAthe RA

Small anterior cardiac veins drain directly into the RASmall anterior cardiac veins drain directly into the RA

Other “thebesian veins” also drain directly into the cardiac Other “thebesian veins” also drain directly into the cardiac chamberschambers


The coronary arteries and veins

Anterior view Posterior view

Anatomy &physiology Seeley et al eighth edition McGraw Hill

The coronary circulation

Pathophysiology McCance & Huether fifth edition Elsevier Mosby

Coronary artery plaque Atheromatous plaque

Pathophysiology by McCance fifth edition Elsevier Mosby

Atheromatous plaque disruption and myocardial infarction

Coronary angiogram showing

stenosis of the LAD

Angioplasty and stenting

Coronary bypass surgery

Davidson’s Principles and Practice of Medicine eighteenth edition Churchill Livingstone

Autonomic innervation of the heart

Marieb &Hoehn Human Anatomy and Phsiolgy seventh editionPearson Benjamin Cummings

The HeartThe Heart

The Conduction SystemThe Conduction System

The conduction system is the electric wiring of the heartThe conduction system is the electric wiring of the heartIts function is to synchronize the sequential contraction of the atria Its function is to synchronize the sequential contraction of the atria

followed by the contraction of the ventriclesfollowed by the contraction of the ventriclesIt is made of specialized cells with unstable resting membrane It is made of specialized cells with unstable resting membrane

potential that allows spontaneous repolarization and potential that allows spontaneous repolarization and depolarizationdepolarization

Repolarization is the building up of an electric difference between theRepolarization is the building up of an electric difference between the inside and the outside of the cell membraneinside and the outside of the cell membraneDepolarization is the return of the two sides of the membrane to Depolarization is the return of the two sides of the membrane to

electric electric neutralityneutralityPolarization is affected by the selective movement of ions across the Polarization is affected by the selective movement of ions across the

membranemembraneThis process requires pump action and energyThis process requires pump action and energy

Resting membrane potential

Vander Physiology tentth edition McGraw Hill

Vander Physiology tenth edition McGraw Hill

Creation of electric potential across the cell membrane through selective ion diffusion

The HeartThe Heart

Conduction SystemConduction System

Sequential systole of the atria followed by the ventricles is the Sequential systole of the atria followed by the ventricles is the result of depolarization of the myocardial cell membraneresult of depolarization of the myocardial cell membrane

Gap junctions between cells allow the spread of the action Gap junctions between cells allow the spread of the action potentialpotential

The initial excitation of a myocardial cell allows the excitation of all The initial excitation of a myocardial cell allows the excitation of all the cells the cells

The HeartThe Heart


Depolarization cycleDepolarization cycle

KK++ channels close, this leads to increased movement of Na channels close, this leads to increased movement of Na++ into the into the cellcell

The cell membrane then becomes less negativeThe cell membrane then becomes less negative

A less negative cell membrane allows CaA less negative cell membrane allows Ca++++ channels to open, Ca channels to open, Ca++++ rushes inrushes in

CaCa++++ rush brings the membrane potential to zero (depolarized) rush brings the membrane potential to zero (depolarized)

Ca channels then close and K channels open increasing the Ca channels then close and K channels open increasing the negativity (repolarization)negativity (repolarization)

The HeartThe Heart


The conduction system Initiates and spreads action potential (an The conduction system Initiates and spreads action potential (an electric current) to cardiac muscle fiberselectric current) to cardiac muscle fibers

The spread (conduction) takes place through specialized cardiac muscle The spread (conduction) takes place through specialized cardiac muscle

Action potential consists of depolarization and repolarization cyclesAction potential consists of depolarization and repolarization cycles

Depolarization depends on the flux of NaDepolarization depends on the flux of Na++ and Ca++ into the cell and Ca++ into the cell through through

their specific gatestheir specific gates

CaCa++++ gates open and close slower than Na+ gates gates open and close slower than Na+ gates

Repolarization occurs as a result of the closure of CaRepolarization occurs as a result of the closure of Ca++++ and opening and opening

of K+ gatesof K+ gates

The cardiac muscle has the ability to depolarize and repolarrize The cardiac muscle has the ability to depolarize and repolarrize autonomicallyautonomically

A refractory period takes place during depolarization/repolarizationA refractory period takes place during depolarization/repolarization

The HeartThe Heart


The cardiac muscle has the ability to depolarize and repolarrize The cardiac muscle has the ability to depolarize and repolarrize autonomicallyautonomically

A refractory period takes place during depolarization/repolarizationA refractory period takes place during depolarization/repolarization

The cardiac muscle can not depolarize during the absolute refractory The cardiac muscle can not depolarize during the absolute refractory periodperiod

And can depolarize under stronger stimulation during the relativeAnd can depolarize under stronger stimulation during the relative

refractory periodrefractory period

The refractory period is longer in the cardiac than the skeletal muscleThe refractory period is longer in the cardiac than the skeletal muscle

This is because there is a ‘ plateau phase that follows cardiac muscleThis is because there is a ‘ plateau phase that follows cardiac muscle

depolarization before reploarization is completedepolarization before reploarization is complete

The refractory period prevents the tetanic contraction of the cardiac The refractory period prevents the tetanic contraction of the cardiac musclemuscle

The HeartThe Heart


Different cardiac muscles have different rates of depolarization and Different cardiac muscles have different rates of depolarization and repolarizationrepolarization

The specialized muscles of the conduction system have faster The specialized muscles of the conduction system have faster depolarization/depolarization/

repolarization rates than the rest of the cardiac musclerepolarization rates than the rest of the cardiac muscle

The cells of the sinoatrial node have the fastest rate in the The cells of the sinoatrial node have the fastest rate in the conduction systemconduction system

The sinoatrial node (SAN) therefore sets the pace for the rate ofThe sinoatrial node (SAN) therefore sets the pace for the rate of

cardiac muscle contractioncardiac muscle contraction

The SAN is therefore called the “pacemaker” under normal conditionsThe SAN is therefore called the “pacemaker” under normal conditions

The HeartThe Heart

The Conduction SystemThe Conduction SystemAnatomyAnatomyThe conduction system is made of The conduction system is made of

Sinoatrial node (SAN) located near the orifice of the SVCSinoatrial node (SAN) located near the orifice of the SVC

Specialized atrial bundles existSpecialized atrial bundles exist

Atrioventricular node is located at the base of the right atriumAtrioventricular node is located at the base of the right atrium

Common bundle (Bundle of His)Common bundle (Bundle of His)

Bundle of His branches run in the IVS and divides into a left andBundle of His branches run in the IVS and divides into a left and

aright “bundle branch”aright “bundle branch”

Purkinje fibers emanate from the bundle branchesPurkinje fibers emanate from the bundle branches

The HeartThe Heart


Normally, the SAN rate of depolarization is faster than the rest of the Normally, the SAN rate of depolarization is faster than the rest of the myocardiummyocardium

The SAN “sets the pace” for the heart rate, it is the normal The SAN “sets the pace” for the heart rate, it is the normal “pacemaker”“pacemaker”

The rate generated is termed “sinus rhythm” The rate generated is termed “sinus rhythm” Conduction through the AVN is slow to allow for the completion of atrial Conduction through the AVN is slow to allow for the completion of atrial systole before the ventricles contractsystole before the ventricles contract If the SAN fails, the AVN takes over, it is inherently slower than the SANIf the SAN fails, the AVN takes over, it is inherently slower than the SAN It generates AV nodal rhythm, simply called “nodal rhythm”It generates AV nodal rhythm, simply called “nodal rhythm” If the AV node also fails, the ventricular muscle takes over, its rhythm is If the AV node also fails, the ventricular muscle takes over, its rhythm is

slower than the nodal, and it is referred to as “idioventricular rhythm”slower than the nodal, and it is referred to as “idioventricular rhythm”

The Heart The Heart


The Action potential spreads from one muscle to the other through The Action potential spreads from one muscle to the other through the gap junctions between the cellsthe gap junctions between the cells

During and following an action potential, the cardiac muscle goes During and following an action potential, the cardiac muscle goes into ainto a

“ “refractory period” during which an excitable membrane can not refractory period” during which an excitable membrane can not bebe

re-excitedre-excited

The refractory period prevents the myocardium from going into The refractory period prevents the myocardium from going into tetanic contractions tetanic contractions

When the conduction between the atria and the ventricle is impaired When the conduction between the atria and the ventricle is impaired the condition is termed “heart block”, this could be partial or the condition is termed “heart block”, this could be partial or completecomplete

Anatomy &physiology Seeley et al eighth edition McGraw Hill

The anatomy of the conduction system


The conduction system

The EKG


Each wave of depolarization is Each wave of depolarization is followed by followed by an absolute refractory period an absolute refractory period during during which no depolarization can take which no depolarization can take placeplaceThe refractory period is equal to the The refractory period is equal to the length of cardiac muscle length of cardiac muscle contractioncontraction This guards against tetanic This guards against tetanic contraction of contraction of the cardiac musclethe cardiac muscle


Events during the cardiac cycle

Systole and diastole in this diagram refer to the ventricles and not the atria

The HeartThe Heart

Cardiac Output (CO)Cardiac Output (CO)

The cardiac output is the volume of blood delivered to the circulation The cardiac output is the volume of blood delivered to the circulation in one minute, i.e. the heart rate (HR) multiplied by the volume in one minute, i.e. the heart rate (HR) multiplied by the volume ejected with ejected with

each heart beat [called the stroke volume (SV)]each heart beat [called the stroke volume (SV)]

Therefore CO = HR X SVTherefore CO = HR X SV

Cardiac output depends onCardiac output depends on

The amount of blood returning to the heart (also called “preload”)The amount of blood returning to the heart (also called “preload”)

Cardiac contractility which determines the amount of blood ejectedCardiac contractility which determines the amount of blood ejected

during every ventricular contraction, the stroke volume (SV)during every ventricular contraction, the stroke volume (SV)

Heart failure is the inability of the CO to meet the metabolic Heart failure is the inability of the CO to meet the metabolic demands of the bodydemands of the body

The HeartThe Heart


The normal cardiac output is 3 L/mThe normal cardiac output is 3 L/m22/ min/ min

Its purpose is to supply adequate amounts of OIts purpose is to supply adequate amounts of O22 to the tissues to the tissues

Normally, CO provides 3 – 4 times the amount of ONormally, CO provides 3 – 4 times the amount of O22 consumed consumed

If the need for OIf the need for O22 increases or decreases chemoreceptors adjust increases or decreases chemoreceptors adjust

the CO proportionatelythe CO proportionately

The adjustment takes place through increasing the heart rate and The adjustment takes place through increasing the heart rate and

contractilitycontractility

Clinically, the urine output, skin temperature brain function are Clinically, the urine output, skin temperature brain function are indices indices

of adequacy of COof adequacy of CO

Factors affecting cardiac output

Vander’s Physiology eighth edition Mc Graw Hill


Control of stroke volume

The HeartThe Heart


The Ejection FractionThe Ejection Fraction

Ventricles do not eject all the blood they accumulate during diastole,Ventricles do not eject all the blood they accumulate during diastole,

the end diastolic volume (EDV)the end diastolic volume (EDV)

The difference between EDV and the volume ejected during systole,The difference between EDV and the volume ejected during systole,

the end systolic volume (ESV) is the “stroke volume” (SV)the end systolic volume (ESV) is the “stroke volume” (SV)

Therefore SV = EDV – ESVTherefore SV = EDV – ESV

The ratio SV/EDV is normally about 55% to 60%The ratio SV/EDV is normally about 55% to 60%

This is the “ejection fraction” (EF)This is the “ejection fraction” (EF)

Reduced cardiac contractility results in a lower EFReduced cardiac contractility results in a lower EF

The HeartThe Heart


The Frank-Starling LawThe Frank-Starling Law

The more stretched the cardiac muscle the stronger its The more stretched the cardiac muscle the stronger its contraction until an optimal length is reached contraction until an optimal length is reached after after

which further stretching will weaken which further stretching will weaken

the force of contractionthe force of contraction

The amount of myocardial stretch is decided by the The amount of myocardial stretch is decided by the preloadpreload

The HeartThe Heart

Cardiac Output (CO)Cardiac Output (CO)Factors Affecting the Heart RateFactors Affecting the Heart RateSympathetic stimulation increases SAN discharge through the Sympathetic stimulation increases SAN discharge through the

effect of effect of

noreadrenalin on the noreadrenalin on the ββ receptors, it also increases the cardiac receptors, it also increases the cardiac contractilitycontractility

Parasympathetic stimulation reduces the SAN rateParasympathetic stimulation reduces the SAN rate

There is no parasympathetic innervation to the ventriclesThere is no parasympathetic innervation to the ventricles

Bradycardia allows for a larger EDVBradycardia allows for a larger EDV

Extreme tachycardia and extreme bradycardia reduce CO; the Extreme tachycardia and extreme bradycardia reduce CO; the first through reducing the SV, and the second through first through reducing the SV, and the second through reducing HRreducing HR

The HeartThe Heart


Cardiac ReflexesCardiac Reflexes Carotid body receptors reduce the heart rate in response to Carotid body receptors reduce the heart rate in response to

hypertension and increases it in response to hypotensionhypertension and increases it in response to hypotension

Bainbridge reflex stretching the right atrial wall produces Bainbridge reflex stretching the right atrial wall produces tachycardiatachycardia

Adrenaline and thyroxine induce tachycardiaAdrenaline and thyroxine induce tachycardia

CaCa++++ injections augment cardiac contraction, excessive Ca injections augment cardiac contraction, excessive Ca++++ stops stops the heart in systolethe heart in systole

KK++ injections lead to heart block and cardiac arrest in diastole injections lead to heart block and cardiac arrest in diastole

How does the failing heart compensate for the loss of contractility?

Vander’s Physiology eighth edition Mc Graw Hill

The HeartThe Heart

Diastolic and Systolic DysfunctionDiastolic and Systolic Dysfunction

Reduced Reduced compliancecompliance of the RV results in a rapid rise of its pressure of the RV results in a rapid rise of its pressure withwith

additional volumeadditional volume

This leads to a reduced EDV compared to a state of normal This leads to a reduced EDV compared to a state of normal compliance at a given pressurecompliance at a given pressure

Low EDV results in a low SV by RV, and consequently by LVLow EDV results in a low SV by RV, and consequently by LV

In pure diastolic dysfunction, RV contractility remains normalIn pure diastolic dysfunction, RV contractility remains normal

The right ventricle does not have to pump the blood too farThe right ventricle does not have to pump the blood too far

The RV is a The RV is a volume pumpvolume pump

The HeartThe Heart

Systolic DysfunctionSystolic Dysfunction

Unlike the RV, LV has to pump the blood for a long distance and Unlike the RV, LV has to pump the blood for a long distance and againstagainst

higher resistance, the LV is a higher resistance, the LV is a pressure pumppressure pumpSystolic dysfunction results from myocardial damage due to chronically Systolic dysfunction results from myocardial damage due to chronically increased after load (systemic hypertension)increased after load (systemic hypertension) Myocardial damage and changes in the LV geometry result in a Myocardial damage and changes in the LV geometry result in a ↓ SV ↓ SV

atat any given EDV, i.e. ↓ejection fractionany given EDV, i.e. ↓ejection fractionBaroreceptors discharge rate drops leading sympathetic stimulation, ↑ HR,Baroreceptors discharge rate drops leading sympathetic stimulation, ↑ HR, ↑ ↑ PR, and ↑ angiotensin II that leads to fluid retention and PR, and ↑ angiotensin II that leads to fluid retention and ↑ ↑ venous pressure causing edema in the lower limbsvenous pressure causing edema in the lower limbsWhen the LV fails to pump all the volume it receives from RV, edema When the LV fails to pump all the volume it receives from RV, edema develops in the lungs develops in the lungs

The Heart. The heart is afist size pump that drives the blood in the arteries and veins throughout...

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Transcript of The Heart. The heart is afist size pump that drives the blood in the arteries and veins throughout...