the heart. the heart is afist size pump that drives the blood in the arteries and veins throughout...
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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
Gross Anatomy and FunctionGross Anatomy and Function
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
Gross Anatomy and FunctionGross Anatomy and Function
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
Moore & Dalley Clinically Oriented Anatomy fifth edition LIPPINCOTT Williams & Wilkins
The right atrium
Frank Netter, M.D., The CIBA Collection Vol V
The cardiac chambers
Moore & Dalley Clinically Oriented Anatomy fifth edition LIPPINCOTT Williams & Wilkins
The left atrium and ventricle
Pathophysiology by McCance, fifth edition, Elsevier Mosby
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
Gross Anatomy and FunctionGross Anatomy and Function
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
Gross Anatomy and FunctionGross Anatomy and Function
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
Vander Physiology eighth edition McGraw Hill
The HeartThe Heart
Gross Anatomy and FunctionGross Anatomy and Function
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
Gross Anatomy and FunctionGross Anatomy and Function
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
Gross Anatomy and FunctionGross Anatomy and Function
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
Gross Anatomy and FunctionGross Anatomy and Function
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
Marieb Human Anatomy & Physiology seventh edition Pearson benjaamin Cummings
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
Pathophysiology by McCance, fifth edition, Elsevier Mosby
Mechanism of muscle contraction
Pathophysiology by McCance, fifth edition, Elsevier Mosby
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
Frank Netter, M.D., The CIBA Collection Vol V
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
The Conduction SystemThe Conduction System
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 SystemThe Conduction System
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 Conduction SystemThe Conduction System
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
The Conduction SystemThe Conduction System
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
The Conduction SystemThe Conduction System
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 Conduction SystemThe Conduction System
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
Frank Netter, M.D., The CIBA Collection Vol V
The conduction system
The EKG
Marieb Human Anatomy & Physiology seventh edition Pearson benjaamin Cummings
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
Vander Physiology eighth edition McGraw Hill
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
Cardiac Output (CO)Cardiac Output (CO)
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
Vander Physiology eighth edition McGraw Hill
Control of stroke volume
The HeartThe Heart
Cardiac Output (CO)Cardiac Output (CO)
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
Cardiac Output (CO)Cardiac Output (CO)
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 Output (CO)Cardiac Output (CO)
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