ch 18

CHAPTER 18: THE CARDIO-VASCULAR SYSTEM: THE HEART

© 2013 Pearson Education, Inc.

Objectives


I. Systemic vs. Pulmonary circuit

II. Heart Anatomy: Chambers and Valves

III. Blood Flow Through the Heart

IV. Cardiac Conduction System

V. Cardiac Cycle

VI. Fetal Heart Defects


The Pulmonary and Systemic Circuits

• The heart is a transport system comprised of two side-by-side pumps– Right side receives oxygen-poor blood from

tissues• Pumps to lungs to get rid of CO2, pick up O2, via

pulmonary (lung) circuit – Left side receives oxygenated blood from

lungs• Pumps to body tissues via systemic circuit



• Receiving chambers of heart:– Right atrium

• Receives blood returning from systemic circuit– Left atrium

• Receives blood returning from pulmonary circuit



• Pumping chambers of heart:– Right ventricle

• Pumps blood through pulmonary circuit– Left ventricle

• Pumps blood through systemic circuit


Capillary beds oflungs where gasexchange occurs

Pulmonary CircuitPulmonaryarteries Pulmonary veins

Aorta and branchesVenaecavae

Leftatrium

LeftventricleRight

atriumRightventricle

Heart

Systemic Circuit

Oxygen-rich,CO2-poor bloodOxygen-poor,CO2-rich blood

Capillary beds of allbody tissues wheregas exchange occurs

Figure 18.1 The systemic and pulmonary circuits.


http://www.youtube.com/watch?v=l7ejcLxKW8c

http://www.youtube.com/watch?v=QXckE_DlFAM

Heart Anatomy• Approximately size of fist• Location:

– In mediastinum between second rib and fifth intercostal space

– On superior surface of diaphragm– Two-thirds of heart to left of midsternal line– Anterior to vertebral column, posterior to

sternum

PLAY

http://www.youtube.com/watch?v=QXckE_DlFAM


Heart Anatomy

• Base (posterior surface) leans toward right shoulder

• Apex points toward left hip• Apical impulse palpated between fifth

and sixth ribs, just below left nipple


Figure 18.2a Location of the heart in the mediastinum.

Midsternal line2nd rib

DiaphragmSternumLocation ofapical impulse


Figure 18.2b Location of the heart in the mediastinum.

Mediastinum

HeartRight lungBody of T7 vertebra

Posterior


Figure 18.2c Location of the heart in the mediastinum.

Superiorvena cava

Pulmonarytrunk

Diaphragm

AortaParietal pleura(cut)

Left lung

Pericardium (cut)

Apex of heart


Coverings of the Heart: Pericardium

• Double-walled sac• Superficial fibrous pericardium

– Protects, anchors to surrounding structures, and prevents overfilling


Pericardium

• Deep two-layered serous pericardium – recall the parietal pericardium and visceral pericardium?– Parietal layer lines internal surface of fibrous

pericardium– Visceral layer (epicardium) on external

surface of heart– The two layers are separated by the fluid-

filled pericardial cavity– Serous fluid decreases friction


Figure 18.3 The pericardial layers and layers of the heart wall.

Pericardium

Myocardium

Pulmonarytrunk Fibrous pericardium

Parietal layer of serous pericardium

Pericardial cavityEpicardium (viscerallayer of serouspericardium)MyocardiumEndocardiumHeart chamber

Heart wall


Homeostatic Imbalance

• Pericarditis– Inflammation of pericardium– Roughens membrane surfaces pericardial

friction rub (creaking sound) heard with stethoscope

– Cardiac tamponade• Excess fluid builds up in the pericardial cavity and

sometimes compresses heart, causing limited pumping ability


Layers of the Heart Wall

• Three layers of heart wall:– Epicardium– Myocardium– Endocardium

• Heart wall is richly vascularized• Epicardium

– Visceral layer of serous pericardium



• Myocardium - ‘muscle heart’ – 2nd layer– Spiral bundles of contractile cardiac muscle

cells – Cardiac skeleton: crisscrossing, interlacing

layer of connective tissue • Anchors cardiac muscle fibers • Supports great vessels and valves• Limits spread of action potentials to specific paths

as the connective tissue is not electrically excitable.

• Links all parts of the heart together



Endocardium – ‘inside the heart’ – 3rd layer• continuous with endothelial lining of blood vessels

– Glistening white sheet of endothelium that rests on a thin connective tissue layer

– Lines heart chambers; covers cardiac skeleton of valves


Figure 18.3 The pericardial layers and layers of the heart wall.

Pericardium

Myocardium

Pulmonarytrunk Fibrous pericardium

Parietal layer of serous pericardium

Pericardial cavityEpicardium (viscerallayer of serouspericardium)MyocardiumEndocardiumHeart chamber

Heart wall


Figure 18.4 The circular and spiral arrangement of cardiac muscle bundles in the myocardium of the heart.

Cardiacmusclebundles


Chambers

• Four chambers:– Two superior atria– Two inferior ventricles

• Interatrial septum – separates atria– Fossa ovalis – remnant of foramen ovale of

fetal heart• Interventricular septum – separates

ventricles


Figure 18.5e Gross anatomy of the heart.

Superior vena cavaRight pulmonary artery

Pulmonary trunkRight atrium

Right pulmonary veins

Fossa ovalisPectinate musclesTricuspid valveRight ventricle

Chordae tendineaeTrabeculae carneaeInferior vena cava

AortaLeft pulmonary arteryLeft atriumLeft pulmonary veins

Mitral (bicuspid) valve

Aortic valvePulmonary valve

Left ventriclePapillary muscleInterventricular septumEpicardiumMyocardiumEndocardium

Frontal section


Chambers and Associated Great Vessels

• Coronary sulcus (atrioventricular groove)– Encircles junction of atria and ventricles

• Anterior interventricular sulcus– Anterior position of interventricular septum

• Posterior interventricular sulcus– Landmark on posteroinferior surface


Atria: The Receiving Chambers

• Auricles– Appendages that increase atrial volume

• Right atrium– Pectinate muscles– Posterior and anterior regions separated by

crista terminalis• Left atrium

– Pectinate muscles only in auricles


Atria: The Receiving Chambers

• Small, thin-walled• Contribute little to propulsion of blood• Three veins empty into right atrium:

– Superior vena cava, inferior vena cava, coronary sinus –

• Four pulmonary veins empty into left atrium

• Which chamber receives deoxygenated blood?


Ventricles: The Discharging Chambers

• Most of the volume of heart• Right ventricle - most of anterior surface• Left ventricle – posteroinferior surface• Trabeculae carneae – irregular ridges of

muscle on walls• Papillary muscles – anchor chordae

tendineae


Ventricles: The Discharging Chambers

• Thicker walls than atria• Actual pumps of heart• Right ventricle

– Pumps blood into pulmonary trunk• Left ventricle

– Pumps blood into aorta (largest artery in body)


Figure 18.5b Gross anatomy of the heart.

Brachiocephalic trunk

Superior vena cava

Right pulmonary arteryAscending aortaPulmonary trunk

Right pulmonary veinsRight atriumRight coronary artery(in coronary sulcus)Anterior cardiac veinRight ventricleRight marginal arterySmall cardiac veinInferior vena cava

Left common carotid artery

Left subclavian arteryAortic archLigamentum arteriosumLeft pulmonary arteryLeft pulmonary veins

Auricle ofleft atrium

Circumflex artery

Left coronary artery(in coronary sulcus)Left ventricle

Great cardiac veinAnterior interventricularartery (in anteriorinterventricular sulcus)Apex

Anterior view


Figure 18.5a Gross anatomy of the heart.

Aortic arch (fat covered)

Pulmonary trunkAuricle of right atrium

Auricle of left atrium

Anterior interventricularartery

Right ventricle

Apex of heart (left ventricle)

Anterior aspect (pericardium removed)


Figure 18.5f Gross anatomy of the heart.

Photograph; view similar to (e)

Superior vena cava Ascending aorta (cut open)

Pulmonary trunk

Aortic valve

Pulmonary valveInterventricularseptum (cut)Left ventricle

Papillary muscles

Right ventricle anteriorwall (retracted)

Trabeculae carneae

Opening to rightatriumChordae tendineae

Right ventricle


Heart Valves

• Ensure unidirectional blood flow through heart• Open and close in response to pressure

changes• Two atrioventricular (AV) valves

– Prevent backflow into atria when ventricles contract– Tricuspid valve (right AV valve)– Mitral valve (left AV valve, bicuspid valve)– Chordae tendineae anchor cusps to papillary

muscles• Hold valve flaps in closed position


1

2

3

Blood returning to the heart fillsatria, pressing against the AV valves.The increased pressure forces AVvalves open.

As ventricles fill, AV valve flapshang limply into ventricles.

1

2 3

Atria contract, forcing additionalblood into ventricles.

Ventricles contract, forcingblood against AV valve cusps.

AV valves close.

Papillary muscles contract andchordae tendineae tighten,preventing valve flaps from evertinginto atria.

AV valves open; atrial pressure greater than ventricular pressure

AV valves closed; atrial pressure less than ventricular pressure

Direction ofblood flow

Cusp ofatrioventricularvalve (open)

Atrium

ChordaetendineaePapillarymuscle

AtriumCusps ofatrioventricularvalve (closed)

Blood inventricle

Ventricle

Figure 18.7 The atrioventricular (AV) valves.


Heart Valves

• Two semilunar (SL) valves– Prevent backflow into ventricles when

ventricles relax– Open and close in response to pressure

changes– Aortic semilunar valve– Pulmonary semilunar valve


As ventricles contract and intraventricular pressure rises, blood is pushed up against semilunar valves, forcing them open.

As ventricles relax and intraventricular pressure falls, blood flows back from arteries, filling the cusps of semilunar valves and forcing them to close.

AortaPulmonarytrunk

Semilunar valves open

Semilunar valves closed

Figure 18.8 The semilunar (SL) valves.


Figure 18.6a Heart valves.Pulmonary valveAortic valve

Area of cutawayMitral valveTricuspid valve

MyocardiumMitral(left atrioventricular)valveTricuspid(right atrioventricular) valveAortic valve

Pulmonary valve

AnteriorCardiacskeleton


Figure 18.6b Heart valves.

Pulmonary valveAortic valve

Area of cutawayMitral valveTricuspid valve

MyocardiumMitral(left atrioventricular)valveTricuspid(right atrioventricular) valveAortic valve

Pulmonary valve


Figure 18.6c Heart valves.Pulmonary valveAortic valve

Area of cutaway

Mitral valveTricuspid valve

Chordae tendineae attached to tricuspid valve flap

Papillary muscle


Figure 18.6d Heart valves.

Pulmonary valveAortic valve

Area of cutaway

Mitral valveTricuspid valve

Opening of inferiorvena cavaTricuspid valve

Myocardium of right ventricle

Papillary muscles

Mitral valveChordae tendineae

Interventricular septum

Myocardium of left ventricle

Video Review of Blood Flow Through the Heart and Heart Anatomy


http://www.youtube.com/watch?v=7XaftdE_h60

http://www.youtube.com/watch?v=7XaftdE_h60



• Two conditions severely weaken heart:– Incompetent or insufficient valve

• Blood backflows so heart repumps same blood over and over

– Valvular stenosis• Stiff flaps – constrict opening heart must exert

more force to pump blood• Valves become stiff due to calcium salt deposits or

scar tissue.

• Valve replaced with mechanical, animal, or cadaver valve


Pathway of Blood Through the Heart

• Pulmonary circuit– Right atrium tricuspid valve right

ventricle– Right ventricle pulmonary semilunar valve

pulmonary trunk pulmonary arteries lungs

– Lungs pulmonary veins left atrium


PLAY Animation: Rotatable heart (sectioned)


• Systemic circuit– Left atrium mitral valve left ventricle– Left ventricle aortic semilunar valve

aorta– Aorta systemic circulation


Figure 18.9 The heart is a double pump, each side supplying its own circuit.Both sides of the heart pump at the same time, but let’s follow one spurt of blood all the way through the system. Oxygen-rich blood

Superior vena cava (SVC)Inferior vena cava (IVC)

Coronary sinusRightatrium

Tricuspidvalve

PulmonarySemilunar

valveRightventricle

Pulmonarytrunk

SVC

IVC

CoronarysinusRightatrium

Tricuspidvalve

Rightventricle

PulmonaryarteriesPulmonarytrunk

Pulmonarysemilunarvalve

To heartOxygen-poor blood returns from the body tissues back to the heart.

Oxygen-poor blood is carriedin two pulmonary arteries tothe lungs (pulmonary circuit)to be oxygenated.

To lungs

Systemiccapillaries

Pulmonarycapillaries

To bodyOxygen-rich blood is delivered to the body tissues (systemic circuit).

Oxygen-rich blood returns to the heart via the four pulmonary veins.

To heart

Pulmonaryveins

Leftatrium

MitralvalveLeftventricle

Aorta

Aorticsemilunarvalve

AorticSemilunar

valveMitralvalveAorta Left

ventricleLeft

atriumFour

pulmonary veins

Oxygen-poor bloodSlide 1


Oxygen-poor blood

Oxygen-rich blood


Coronary sinus

SVC

IVC

Coronarysinus

Slide 2Figure 18.9 The heart is a double pump, each side supplying its own circuit.



Oxygen-poor bloodOxygen-rich blood



SVC

IVC

Coronarysinus

Rightatrium


Figure 18.9 The heart is a double pump, each side supplying its own circuit. Slide 4




Tricuspidvalve Right

ventricle

SVC

IVC

Coronarysinus

Rightatrium

Tricuspidvalve

Rightventricle



Oxygen-poor blood

Oxygen-rich blood


Coronary sinus

Rightatrium

Tricuspidvalve

PulmonarySemilunar

valveRightventricle

Pulmonarytrunk

SVC

IVC

Coronarysinus

Rightatrium

Tricuspidvalve

Rightventricle

Pulmonaryarteries

Pulmonarytrunk



Figure 18.9 The heart is a double pump, each side supplying its own circuit. Slide 6Oxygen-poor blood

Oxygen-rich blood



Tricuspidvalve

PulmonarySemilunar

valveRightventricle

Pulmonarytrunk

SVC

IVC

Coronarysinus

Rightatrium

Tricuspidvalve

Rightventricle

Pulmonaryarteries

Pulmonarytrunk


Oxygen-poor blood is carriedin two pulmonary arteries to the lungs (pulmonary circuit)to be oxygenated.

To lungs



Oxygen-poor bloodOxygen-rich bloodPulmonary

veins

Four pulmonary

veins




Pulmonaryveins

Leftatrium

Leftatrium

Four pulmonary

veins

Blood Flow Through the Heart

Oxygen-poor blood

Oxygen-rich blood

Rightventricle




Pulmonaryveins

Leftatrium


MitralvalveLeft

ventricleLeft

atriumFour

pulmonary veins



Oxygen-poor blood

Oxygen-rich bloodRight

ventricle

Pulmonaryveins

Leftatrium


Aorta


AorticSemilunar


ventricleLeft

atriumFour

pulmonary veins



Blood Flow Through the Heart

Systemiccapillaries

To body

Oxygen-rich blood is delivered to the body tissues (systemic circuit).

Pulmonaryveins

Leftatrium


Aorta


AorticSemilunar


ventricleLeft

atriumFour

pulmonary veins

Oxygen-poor blood

Oxygen-rich blood


Figure 18.9 The heart is a double pump, each side supplying its own circuit. Slide 12Both sides of the heart pump at the same time, but let’s follow one spurt of blood all the way through the system. Oxygen-rich blood



Tricuspidvalve

PulmonarySemilunar

valveRightventricle

Pulmonarytrunk

SVC

IVC

CoronarysinusRightatrium

Tricuspidvalve

Rightventricle

PulmonaryarteriesPulmonarytrunk


To heartOxygen-poor blood returns from the body tissues back to the heart.

Oxygen-poor blood is carriedin two pulmonary arteries tothe lungs (pulmonary circuit)to be oxygenated.

To lungs

Systemiccapillaries


To bodyOxygen-rich blood is delivered to the body tissues (systemic circuit).

Oxygen-rich blood returns to the heart via the four pulmonary veins.

To heart

Pulmonaryveins

Leftatrium


Aorta


AorticSemilunar


ventricleLeft

atriumFour

pulmonary veins

Oxygen-poor blood



• Equal volumes of blood pumped to pulmonary and systemic circuits

• Pulmonary circuit short, low-pressure circulation• Systemic circuit long, high-friction circulation;

encounters 5X more resistance to blood flow than the pulmonary circulation.

• Anatomy of ventricles reflects differences– Left ventricle walls 3X thicker than right

• Pumps with greater pressure


Figure 18.10 Anatomical differences between the right and left ventricles.

Rightventricle

Interventricularseptum

Leftventricle


Coronary Circulation

• Functional blood supply to heart muscle itself– Delivered when heart relaxed– Left ventricle receives most blood supply

• Arterial supply varies among individuals• Contains many anastomoses (junctions)

– Provide additional routes for blood delivery– Cannot compensate for coronary artery

occlusion


Coronary Circulation: Arteries

• Arteries arise from base of aorta• Left coronary artery branches anterior

interventricular artery and circumflex artery– Supplies interventricular septum, anterior ventricular

walls, left atrium, and posterior wall of left ventricle• Right coronary artery branches right

marginal artery and posterior interventricular artery– Supplies right atrium and most of right ventricle


AortaSuperiorvena cava

Anastomosis(junction ofvessels)

RightatriumRightcoronaryartery

Rightventricle

Rightmarginalartery

Posteriorinterventricularartery

Anterior interventricularartery

Leftventricle

Circumflexartery

Leftcoronaryartery

Left atrium

Pulmonarytrunk

The major coronary arteries

Figure 18.11a Coronary circulation.


Coronary Circulation: Veins

• Cardiac veins collect blood from capillary beds• Coronary sinus empties into right atrium;

formed by merging cardiac veins– Great cardiac vein of anterior interventricular sulcus– Middle cardiac vein in posterior interventricular

sulcus– Small cardiac vein from inferior margin

• Several anterior cardiac veins empty directly into right atrium anteriorly


Figure 18.11b Coronary circulation.

Superiorvena cava

Anteriorcardiacveins

Smallcardiac vein Middle cardiac vein

Coronarysinus

Greatcardiacvein

The major cardiac veins


Figure 18.5d Gross anatomy of the heart.

Aorta

Left pulmonary artery

Left pulmonary veins

Auricle of left atriumLeft atrium

Great cardiac vein

Posterior vein ofleft ventricleLeft ventricle

Apex

Superior vena cavaRight pulmonary arteryRight pulmonary veins

Right atriumInferior vena cavaCoronary sinusRight coronary artery(in coronary sulcus)Posterior interventricularartery (in posteriorinterventricular sulcus)Middle cardiac veinRight ventricle

Posterior surface view


Homeostatic Imbalances

• Angina pectoris– Thoracic pain caused by fleeting deficiency in

blood delivery to myocardium– Cells weakened

• Myocardial infarction (heart attack)– Prolonged coronary blockage– Areas of cell death repaired with

noncontractile scar tissue


Microscopic Anatomy of Cardiac Muscle

• Cardiac muscle cells striated, short, branched, fat, interconnected, 1 (perhaps 2) central nuclei

• Connective tissue matrix (endomysium) connects to cardiac skeleton– Contains numerous capillaries

• T tubules wide, less numerous; SR simpler than in skeletal muscle

• Numerous large mitochondria (25–35% of cell volume)


Figure 18.12a Microscopic anatomy of cardiac muscle.

NucleusIntercalated

discsCardiac

muscle cell Gap junctions Desmosomes


Microscopic Anatomy of Cardiac Muscle

• Intercalated discs - junctions between cells - anchor cardiac cells – Desmosomes prevent cells from separating

during contraction– Gap junctions allow ions to pass from cell to

cell; electrically couple adjacent cells• Allows heart to be functional syncytium

– Behaves as single coordinated unit


Figure 18.12b Microscopic anatomy of cardiac muscle.

Cardiac muscle cellIntercalated disc

Mitochondrion Nucleus

MitochondrionT tubuleSarcoplasmicreticulum Z disc

I band A band I band

NucleusSarcolemma

Cardiac Conduction System

• is a group of specialized cardiac muscle cells in the walls of the heart that send signals to the heart muscle causing it to contract. The main components of the cardiac conduction system are the SA node, AV node, bundle of His, bundle branches, and Purkinje fibers.



Heart Physiology: Electrical Events

• Heart depolarizes and contracts without nervous system stimulation– Rhythm can be altered by autonomic nervous

system


Heart Physiology: Setting the Basic Rhythm

• Coordinated heartbeat is a function of– Presence of gap junctions– Intrinsic cardiac conduction system

• Network of noncontractile (autorhythmic) cells• Initiate and distribute impulses coordinated

depolarization and contraction of heart


Pacemaker (Autorhythmic) Cells

• Have unstable resting membrane potentials (pacemaker potentials or prepotentials) due to opening of slow Na+ channels– Continuously depolarize

• At threshold, Ca2+ channels open • Explosive Ca2+ influx produces the rising phase

of the action potential• Repolarization results from inactivation of Ca2+

channels and opening of voltage-gated K+ channels


Action Potential Initiation by Pacemaker Cells• Three parts of action potential:

– Pacemaker potential• Repolarization closes K+ channels and opens slow

Na+ channels ion imbalance – Depolarization

• Ca2+ channels open huge influx rising phase of action potential

– Repolarization• K+ channels open efflux of K+


Figure 18.14 Pacemaker and action potentials of pacemaker cells in the heart. Slide 1

1

23

23

1

Mem

bran

e po

tent

ial (

mV) +10

0–10–20–30–40–50–60–70

Time (ms)

Actionpotential

Threshold

Pacemakerpotential

1

2

3

Pacemaker potential This slow depolarization is due to both opening of Na+ channels and closing of K+ channels. Notice that the membrane potential is never a flat line. Depolarization The action potential begins when the pacemaker potential reaches threshold. Depolarization is due to Ca2+ influx through Ca2+

channels.

Repolarization is due to Ca2+ channels inactivating and K+ channels opening. This allows K+ efflux, which brings the membrane potential back to its most negative voltage.



1 1

+100

–10–20–30–40–50–60–70

Time (ms)

Actionpotential

Threshold

Pacemakerpotential

1 Pacemaker potential This slow depolarization is due to both opening of Na+ channels and closing of K+ channels. Notice that the membrane potential is never a flat line.

Mem

bran

e po

tent

ial (

mV)



1

2 2

1

+100

–10–20–30–40–50–60–70

Time (ms)

Actionpotential

Threshold

Pacemakerpotential

1

2


channels.

Mem

bran

e po

tent

ial (

mV)



1

23

23

1

Mem

bran

e po

tent

ial (

mV) +10

0–10–20–30–40–50–60–70

Time (ms)

Actionpotential

Threshold

Pacemakerpotential

1

2

3


channels.

Repolarization is due to Ca2+ channels inactivating and K+ channels opening. This allows K+ efflux, which brings the membrane potential back to its most negative voltage.


Sequence of Excitation

• Cardiac pacemaker cells pass impulses, in order, across heart in ~220 ms– Sinoatrial node – Atrioventricular node – Atrioventricular bundle – Right and left bundle branches – Subendocardial conducting network

(Purkinje fibers)


Heart Physiology: Sequence of Excitation

• Sinoatrial (SA) node– Pacemaker of heart in right atrial wall

• Depolarizes faster than rest of myocardium– Generates impulses about 75X/minute (sinus

rhythm)• Inherent rate of 100X/minute tempered by extrinsic

factors

• Impulse spreads across atria, and to AV node



• Atrioventricular (AV) node– In inferior interatrial septum– Delays impulses approximately 0.1 second

• Because fibers are smaller diameter, have fewer gap junctions

• Allows atrial contraction prior to ventricular contraction

– Inherent rate of 50X/minute in absence of SA node input



• Atrioventricular (AV) bundle(bundle of His)– In superior interventricular septum– Only electrical connection between atria and

ventricles• Atria and ventricles not connected via gap

junctions



• Right and left bundle branches– Two pathways in interventricular septum– Carry impulses toward apex of heart



• Subendocardial conducting network– Complete pathway through interventricular

septum into apex and ventricular walls– More elaborate on left side of heart– AV bundle and subendocardial conducting

network depolarize 30X/minute in absence of AV node input

• Ventricular contraction immediately follows from apex toward atria


Figure 18.15a Intrinsic cardiac conduction system and action potential succession during one heartbeat.

The sinoatrial (SA) node (pacemaker)generates impulses.

1

The impulsespause (0.1 s) at theatrioventricular(AV) node.

2

The atrioventricular(AV) bundleconnects the atriato the ventricles.

3

The bundle branches conduct the impulses through the interventricular septum.

4

The subendocardialconducting networkdepolarizes the contractilecells of both ventricles.

5

Superior vena cava Right atrium

Left atrium

Subendocardialconductingnetwork(Purkinje fibers)

Inter-ventricularseptum

Anatomy of the intrinsic conduction system showing the sequence ofelectrical excitation

Internodal pathway

Slide 1




1Superior vena cava Right atrium

Left atrium




Slide 2

Internodal pathway




1


2


Left atrium




Slide 3

Internodal pathway




1


2


3


Left atrium




Slide 4

Internodal pathway




1


2


3


4


Left atrium




Slide 5

Internodal pathway




1


2


3


4

The subendocardialconducting networkdepolarizes the contractilecells of both ventricles.

5


Left atrium




Slide 6

Internodal pathway


Mechanical Events: The Cardiac Cycle

• Cardiac cycle– Blood flow through heart during one complete

heartbeat: atrial systole and diastole followed by ventricular systole and diastole

– Systole—contraction – Diastole—relaxation– Series of pressure and blood volume changes


Phases of the Cardiac Cycle

• 1. Ventricular filling—takes place in mid-to-late diastole– AV valves are open; pressure low – 80% of blood passively flows into ventricles– Atrial systole occurs, delivering remaining

20%– End diastolic volume (EDV): volume of

blood in each ventricle at end of ventricular diastole



• 2. Ventricular systole– Atria relax; ventricles begin to contract – Rising ventricular pressure closing of AV

valves– Isovolumetric contraction phase (all valves

are closed)– In ejection phase, ventricular pressure

exceeds pressure in large arteries, forcing SL valves open

– End systolic volume (ESV): volume of blood remaining in each ventricle after systole



• 3. Isovolumetric relaxation - early diastole– Ventricles relax; atria relaxed and filling– Backflow of blood in aorta and pulmonary

trunk closes SL valves• Causes dicrotic notch (brief rise in aortic pressure

as blood rebounds off closed valve)• Ventricles totally closed chambers

– When atrial pressure exceeds that in ventricles AV valves open; cycle begins again at step 1


ElectrocardiogramHeart sounds

Left heartQRS

P T P

1st 2nd

Dicrotic notch120

Aorta

Left ventricle

Left atriumAtrial systole

80

40

0

Pres

sure

(mm

Hg)

EDV

SV

ESV

120

50

Vent

ricul

arvo

lum

e (m

l)

Atrioventricular valvesAortic and pulmonary valves

Phase

Open Closed OpenClosed Open Closed

1 2a 2b 3 1

Left atriumRight atriumLeft ventricleRight ventricle

Ventricularfilling

Atrialcontraction

Isovolumetriccontraction phase

Ventricularejection phase

Isovolumetricrelaxation

Ventricularfilling

Ventricular filling(mid-to-late diastole)

Ventricular systole(atria in diastole)

Early diastole

1 2a 2b 3

Figure 18.21 Summary of events during the cardiac cycle.


Homeostatic Imbalances

• Tachycardia - abnormally fast heart rate (>100 beats/min)– If persistent, may lead to fibrillation

• Bradycardia - heart rate slower than 60 beats/min– May result in grossly inadequate blood

circulation in nonathletes– May be desirable result of endurance training



• Congestive heart failure (CHF)– Progressive condition; CO is so low that blood

circulation inadequate to meet tissue needs– Reflects weakened myocardium caused by

• Coronary atherosclerosis—clogged arteries• Persistent high blood pressure• Multiple myocardial infarcts• Dilated cardiomyopathy (DCM)



• Pulmonary congestion– Left side fails blood backs up in lungs

• Peripheral congestion– Right side fails blood pools in body organs

edema• Failure of either side ultimately weakens

other• Treat by removing fluid, reducing

afterload, increasing contractility


Developmental Aspects of the Heart

• Embryonic heart chambers– Sinus venosus– Atrium– Ventricle– Bulbus cordis


Figure 18.24 Development of the human heart.

Day 20: Endothelial tubes begin to fuse.

4a4

32

1

Tubularheart

Day 22:Heart starts pumping.

Arterial end

Ventricle

Ventricle

Venous endDay 24: Heart continues to elongate and starts to bend.

Arterial end

Atrium

Venous end

Day 28: Bending continues as ventricle moves caudally and atrium moves cranially.

AortaSuperiorvena cava

Inferiorvena cava

Ductusarteriosus

PulmonarytrunkForamenovale

Ventricle

Day 35: Bending is complete.



• Fetal heart structures that bypass pulmonary circulation– Foramen ovale connects two atria

• Remnant is fossa ovalis in adult – Ductus arteriosus connects pulmonary trunk

to aorta• Remnant - ligamentum arteriosum in adult

– Close at or shortly after birth



• Congenital heart defects– Most common birth defects; treated with

surgery– Most are one of two types:

• Mixing of oxygen-poor and oxygen-rich blood, e.g., septal defects, patent ductus arteriosus

• Narrowed valves or vessels increased workload on heart, e.g., coarctation of aorta

– Tetralogy of Fallot• Both types of disorders present


Figure 18.25 Three examples of congenital heart defects.

Occurs inabout 1 in every500 births

Ventricular septal defect.The superior part of theinter-ventricular septum failsto form, allowing blood to mixbetween the two ventricles.More blood is shunted fromleft to right because the leftventricle is stronger.

Narrowedaorta


Coarctation of the aorta.A part of the aorta isnarrowed, increasing theworkload of the left ventricle.


Tetralogy of Fallot.Multiple defects (tetra =four): (1) Pulmonary trunktoo narrow and pulmonaryvalve stenosed, resulting in(2) hypertrophied rightventricle; (3) ventricularseptal defect; (4) aortaopens from both ventricles.


Age-Related Changes Affecting the Heart

• Sclerosis and thickening of valve flaps• Decline in cardiac reserve• Fibrosis of cardiac muscle• Atherosclerosis

ch 18

Healthcare