The Circulatory The Circulatory SystemSystemThe HeartThe Heart

Anatomy & Physiology IIChapter 14

Circulatory System: The Circulatory System: The HeartHeartcardiology – the scientific study of the

heart and the treatment of its disorderscardiovascular system

◦ heart and blood vessels

circulatory system ◦ heart, blood vessels, and the blood

major divisions of circulatory system◦ pulmonary circuit - right side of heart

carries blood to lungs for gas exchange and back to heart

◦ systemic circuit - left side of heart supplies oxygenated blood to all tissues of the body

and returns it to the heart

Circulation and the HeartCirculation and the Heart

CirculationContinuous one-way circuit of the

blood vesselsPropelled by heart

Cardiovascular System Cardiovascular System CircuitCircuit

left side of heart◦ fully oxygenated blood

arrives from lungs via pulmonary veins

◦ blood sent to all organs of the body via aorta

right side of heart◦ lesser oxygenated

blood arrives from inferior and superior vena cava

◦ blood sent to lungs via pulmonary trunk

Systemic circuit

Pulmonary circuit

O2-poor,CO2-rich

blood

O2CO2

O2-rich,CO2-poor

blood

CO2 O2

Location of the HeartLocation of the Heart

Between the lungsLeft of the midline of the bodyIn mediastinumApex pointed toward left

Position, Size, and ShapePosition, Size, and Shapeheart located in

mediastinum, between lungs

base – wide, superior portion of heart, blood vessels attach here

apex - inferior end, tilts to the left, tapers to point

weighs 10 oz.

Right lung

Aorta

Diaphragm

Superiorvena cava

Parietalpleura (cut)

Pericardialsac (cut)

Pulmonarytrunk

Base ofheart

Apexof heart

Heart WallHeart Wallepicardium (visceral pericardium)

◦ serous membrane covering heart◦ coronary blood vessels travel through this layer

endocardium ◦ smooth inner lining of heart and blood vessels◦ covers the valve surfaces and continuous with

endothelium of blood vesselsmyocardium

◦ layer of cardiac muscle muscle spirals around heart which produces wringing

motion◦ fibrous skeleton of the heart - framework of

collagenous and elastic fibers provides structural support and attachment for cardiac

muscle and anchor for valve tissue electrical insulation between atria and ventricles important

in timing and coordination of contractile activity

The serous pericardium covers the heart and lines the fibrous pericardium.

ZOOMING IN • Which layer

of the heart wall is the thickest?

The Heart Wall and The Heart Wall and Pericardium Pericardium

Pericardium (pericardial Pericardium (pericardial sac)sac)pericardium - double-walled sac that encloses the

heart◦ allows heart to beat without friction, provides room to

expand, yet resists excessive expansion◦ anchored to diaphragm inferiorly and sternum anteriorly

parietal pericardium – outer wall of sac; has two layers◦ superficial fibrous layer of connective tissue ◦ a deep, thin serous layer

visceral pericardium (epicardium) – heart covering◦ serous lining of sac turns inward at base of heart to cover

the heart surface

pericardial cavity - space inside the pericardial sac (between the visceral and parietal pericardium) filled with pericardial fluid

pericarditis – inflammation of the membranes◦ painful friction rub with each heartbeat

Pericardium and Pericardium and Heart Heart WallWall

Pericardial sac

Epicardium

Myocardium

Endocardium

Epicardium

Pericardial cavity

Pericardialsac:

Fibrouslayer

Serouslayer

Special Features of the Special Features of the MyocardiumMyocardiumCardiac muscles

Are lightly striated (striped)

Have single nucleus cells

Are controlled involuntarily

Have intercalated disks

Have branching muscle fibers

Divisions of the HeartDivisions of the Heart

Double pump

Right side pumps O2-poor / CO2-rich blood to the lungs

◦Pulmonary circuit

Left side pumps oxygenated (CO2-rich) blood to remainder of body

◦Systemic circuit

Four ChambersFour ChambersRight atrium

◦Receives low-oxygen blood returning from body tissue through superior vena cava and inferior vena cava

Left atrium◦Receives high-oxygen blood from lungs

Right ventricle◦Pumps blood from right atrium to lungs

Left ventricle◦Pumps oxygenated blood to body

The right side of the heart pumps blood through the pulmonary circuit to the lungs to be oxygenated;

the left side of the heart pumps blood through the systemic circuit to all other parts of the body.

ZOOMING IN • What vessel carries

blood into the systemic circuit?

The Heart as a Double PumpThe Heart as a Double Pump

ZOOMING IN • Which

heart chamber has the thickest wall?

The Heart and Great The Heart and Great Vessels Vessels

Blood Flow Through HeartBlood Flow Through Heart

blood pathway travels from the right atrium through the body and back to the starting point

3

6

4

55

2

1

7

8

9

Aorta

Pulmonary trunk

Aortic valve

Left atrium

Left ventricle

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2

3

4

5

6

7

8

9

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1

Blood returns to heart via venae cavae.

Superiorvena cava

Rightpulmonaryveins

Rightatrium

Right AV(tricuspid) valve

Rightventricle

Inferiorvena cava

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11

10

Left AV(bicuspid) valve

Left pulmonaryveins

Left pulmonaryartery

Blood enters right atrium from superiorand inferior venae cavae.

Blood in right atrium flows through rightAV valve into right ventricle.

Contraction of right ventricle forcespulmonary valve open.

Blood is distributed by right and leftpulmonary arteries to the lungs, where itunloads CO2 and loads O2.

Blood returns from lungs via pulmonaryveins to left atrium.

Blood in left atrium flows through left AVvalve into left ventricle.

Contraction of left ventricle (simultaneous withstep 3 ) forces aortic valve open.

Blood flows through aortic valve intoascending aorta.

Blood in aorta is distributed to every organ inthe body, where it unloads O2 and loads CO2.

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Blood flows through pulmonary valveinto pulmonary trunk.

Four ValvesFour ValvesValves ensure a one-way flow of

blood through the heart

Atrioventricular valves◦Entrance valves

Right AV (tricuspid) and Left AV (bicuspid)

Semilunar valves◦Exit valves

Pulmonary and Aortic

Heart ValvesHeart Valvesatrioventricular (AV) valves – controls blood

flow between atria and ventricles

◦ Triscupid valve has 3 cusps

◦ Bicuspid (miral) valve has 2 cusps

◦ chordae tendineae - cords connect AV valves to papillary muscles on floor of ventricles

prevent AV valves from flipping inside out or bulging into the atria when the ventricles contract

semilunar valves - control flow into great arteries – open and close because of blood flow and pressure

◦ pulmonary semilunar valve - in opening between right ventricle and pulmonary trunk

◦ aortic semilunar valve in opening between left ventricle and aorta

Heart ValvesHeart Valves

Right AV(tricuspid) valve

Fibrousskeleton

Openings tocoronary arteries

Aorticvalve

Pulmonaryvalve

Left AV(bicuspid) valve

Blood Supply to the Blood Supply to the MyocardiumMyocardium

Coronary circulationRight coronary arteryLeft coronary arteryCoronary sinus

Coronary CirculationCoronary Circulation 5% of blood pumped by heart is pumped to the heart itself

through the coronary circulation to sustain its strenuous workload◦ 250 ml of blood per minute

◦ needs abundant O2 and nutrients

left coronary artery (LCA) branch off the ascending aorta◦ anterior interventricular branch

supplies blood both ventricles and anterior two-thirds of the interventricular septum

◦ circumflex branch supplies left atrium and posterior wall of left ventricle

right coronary artery (RCA) branch off the ascending aorta◦ supplies right atrium and sinoatrial node (pacemaker)

◦ right marginal branch supplies lateral aspect of right atrium and ventricle

◦ posterior interventricular branch supplies posterior walls of ventricles

Coronary Vessels - Coronary Vessels - PosteriorPosterior

Left atrium

Left ventricle

Apex of heart

Right ventricle

Right atrium

Aorta

Posterior view

Fat

Inferior vena cava

Coronary sulcus

Coronary sinus

Left pulmonaryartery

Left pulmonaryveins

Superiorvena cava

Right pulmonaryartery

Right pulmonaryveins

Posteriorinterventricular

sulcus

(A) When the left ventricle contracts, the aortic valve opens. The valve cusps prevent filling of the coronary arteries.

(B) When the left ventricle relaxes, backflow of blood closes the aortic valve and the coronary arteries fill.

Opening of coronary arteries in Opening of coronary arteries in the aortic valve (anterior view). the aortic valve (anterior view).

Coronary Blood FlowCoronary Blood Flowblood flow to the heart muscle during

ventricular contraction is slowed, unlike the rest of the body

three reasons:◦ contraction of the myocardium compresses

the coronary arteries and obstructs blood flow◦ opening of the aortic valve flap during

ventricular systole covers the openings to the coronary arteries blocking blood flow into them

◦ during ventricular diastole, blood in the aorta surges back toward the heart and into the openings of the coronary arteries blood flow to the myocardium increases during

ventricular relaxation

AnginaAnginaangina pectoris – chest pain from partial

obstruction of coronary blood flow

◦ pain caused by ischemia of cardiac muscle

◦ obstruction partially blocks blood flow

◦ myocardium shifts to anaerobic fermentation producing lactic acid stimulating pain

Myocardial Infarction (heart Myocardial Infarction (heart attack)attack) Interruption of blood supply to the heart from a

blood clot or fatty deposit (atheroma)

can cause death of cardiac cells within minutes

Some protection from MI is provided by arterial anastomoses which provides an alternative route of blood flow (collateral circulation) within the myocardium

Myocardial Infarction (heart Myocardial Infarction (heart attack)attack)myocardial infarction (MI) – sudden death of a

patch of myocardium resulting from long-term obstruction of coronary circulation

◦ atheroma (blood clot or fatty deposit) often obstruct coronary arteries

◦ cardiac muscle downstream of the blockage dies

◦ heavy pressure or squeezing pain radiating into the left arm

◦ some painless heart attacks may disrupt electrical conduction pathways, lead to fibrillation and cardiac arrest

silent heart attacks occur in diabetics & elderly

MI responsible for about half of all deaths in the United States

Cardiac Conduction Cardiac Conduction SystemSystemElectrical energy stimulates heart

muscleNodes

◦Sinoatrial (SA) node (pacemaker)

◦Atrioventricular (AV) node

Specialized fibers◦Atrioventricular bundle (bundle of His)

◦Purkinje fibers (conduction myofibers)The sinoatrial (SA) node, the atrioventricular

(AV) node, and specialized fibers conduct the electrical energy that stimulates the heart muscle to contract.

Cardiac Conduction Cardiac Conduction SystemSystem

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1

1

2

3

4 5

2Right atrium

Purkinje fibers

Sinoatrial node(pacemaker)

Atrioventricularnode

Atrioventricularbundle

SA node fires.

Excitation spreads throughatrial myocardium.

AV node fires.

Excitation spreads down AVbundle.

Purkinje fibers distributeexcitation throughventricular myocardium.

Leftatrium

Purkinjefibers

Bundlebranches

The Conduction PathwayThe Conduction Pathway

Sinus rhythmSinoatrial (SA) node Atria Atrioventricular (AV) nodeInternodal pathwaysBundle of HisBundle branches and Purkinje

fibersVentricles

Function of the HeartFunction of the Heart

Left and right sides of heart work together in cardiac cycle (heartbeat)

Systole (active phase, contraction)

Diastole (resting phase)

Electrocardiogram (ECG or Electrocardiogram (ECG or EKG)EKG)composite of all action potentials of

nodal and myocardial cells detected, amplified and recorded by electrodes on arms, legs and chest

0.8 second

+1

0

–1

Mil

livo

lts

T wave

QRS interval

R R

QS

P wave

PRinterval

QTinterval

PQsegment

STsegment

Ventriclescontract

Atriacontract

Atriacontract

Ventriclescontract

EKG DeflectionsEKG DeflectionsP wave

◦ SA node fires, atria depolarize and contract◦ atrial systole begins 100 msec after SA signal

QRS complex◦ ventricular depolarization◦ complex shape of spike due to different

thickness and shape of the two ventricles

ST segment - ventricular systole ◦ plateau in myocardial action potential

T wave◦ ventricular repolarization and relaxation

Normal Electrocardiogram Normal Electrocardiogram (ECG)(ECG)

0.8 second

+1

0

–1

Mill

ivo

lts T wave

QRS interval

R R

QS

P wave

PRinterval

QTinterval

PQsegment

STsegment

Ventriclescontract

Atriacontract

Atriacontract

Ventriclescontract

1) atrial depolarization begins

2) atrial depolarization complete (atria contracted)

3) ventricles begin to depolarize at apex; atria repolarize (atria relaxed)

4) ventricular depolarization complete (ventricles contracted)

5) ventricles begin to repolarize at apex

6) ventricular repolarization complete (ventricles relaxed)

Electrical Activity of Electrical Activity of MyocardiumMyocardium

5

6

1 4

2

T

SQ

R

P

T

SQ

R

P

SQ

R

P

Q

R

P

P

P

3

KeyWave of

depolarizationWave of

repolarization

Atria begin depolarizing.

Atrial depolarization complete.

Ventricular depolarization complete.

Ventricular repolarization begins at apexand progresses superiorly.

Ventricular repolarization complete; heartis ready for the next cycle.

Ventricular depolarization begins at apexand progresses superiorly as atria repolarize.

Diagnostic Value of ECGDiagnostic Value of ECG

abnormalities in conduction pathways

myocardial infarction

nodal damage

heart enlargement

electrolyte and hormone imbalances

ECGs: Normal and ECGs: Normal and AbnormalAbnormal

abnormalities in conduction pathways

myocardial infarction

heart enlargement

electrolyte and hormone imbalances

(a) Sinus rhythm (normal)

(b) Nodal rhythm—no SA node activity

Cardiac CycleCardiac Cyclecardiac cycle - one complete contraction

and relaxation of all four chambers of the heart

atrial systole (contraction) occurs while ventricles are in diastole (relaxation)

atrial diastole occurs while ventricles in systole

quiescent period all four chambers relaxed at same time

questions to solve – how does pressure affect blood flow? and how are heart sounds produced?

Timing of Cardiac CycleTiming of Cardiac Cyclein a resting person

◦atrial systole last about 0.1 sec

◦ventricular systole about 0.3 sec

◦quiescent period, when all four chambers are in diastole, 0.4 sec

total duration of the cardiac cycle is therefore 0.8 sec in a heart beating 75 bpm

ZOOMING IN • When the ventricles contract, what valves close? What valves open?

The Cardiac CycleThe Cardiac Cycle

Ventricular FillingVentricular Fillingduring diastole, ventricles expand

◦ their pressure drops below that of the atria◦ AV valves open and blood flows into the ventricles

end-diastolic volume (EDV) – amount of blood contained in each ventricle at the end of ventricular filling◦ 130 mL of blood

Ventricular EjectionVentricular Ejectionejection of blood begins when the ventricular

pressure exceeds arterial pressure and forces semilunar valves open

blood spurts out of each ventricle rapidly at first – rapid ejection

then more slowly under reduced pressure – reduced ejection

stroke volume (SV) of about 70 mL of blood is ejected of the 130 mL in each ventricle

◦ ejection fraction of about 54%

◦ as high as 90% in vigorous exercise

end-systolic volume (ESV) – the 60 mL of blood left behind

Overview of Volume Overview of Volume Changes Changes

end-systolic volume (ESV) 60 ml-passively added to ventricle during atrial diastole +30 ml-added by atrial systole +40 ml

total: end-diastolic volume (EDV) 130 mlstroke volume (SV) ejected

by ventricular systole -70 ml

leaves: end-systolic volume (ESV) 60 ml

both ventricles must eject same amount of blood

Unbalanced Ventricular Unbalanced Ventricular OutputOutput

pulmonary edemaPressure backs up.

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2

3

(a) Pulmonary edema

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1

Right ventricularoutput exceeds leftventricular output.

Fluid accumulates inpulmonary tissue.

Unbalanced Ventricular Unbalanced Ventricular OutputOutput

peripheral edemaPressure backs up.

1

2

3

(b) Systemic edema

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3

Left ventricularoutput exceeds rightventricular output.

Fluid accumulates insystemic tissue.

Congestive Heart FailureCongestive Heart Failurecongestive heart failure (CHF) - results from the

failure of either ventricle to eject blood effectively

◦ usually due to a heart weakened by myocardial infarction, chronic hypertension, valvular insufficiency, or congenital defects in heart structure.

left ventricular failure – blood backs up into the lungs causing pulmonary edema

◦ shortness of breath or sense of suffocation

right ventricular failure – blood backs up in the vena cava causing systemic or generalized edema

◦ enlargement of the liver, ascites (pooling of fluid in abdominal cavity), distension of jugular veins, swelling of the fingers, ankles, and feet

eventually leads to total heart failure

Cardiac Output (CO)Cardiac Output (CO)cardiac output (CO) – the amount ejected by

ventricle in 1 minutecardiac reserve – the difference between a

person’s maximum and resting CO◦ increases with fitness, decreases with disease

to keep cardiac output constant as we increase in age, the heart rate increases as the stroke volume decreases

Cardiac Output (CO)Cardiac Output (CO)Calculating cardiac output Cardiac output (CO)Stroke volume (SV)Heart rate (HR)cardiac output = heart rate x stroke volume

◦CO = HR x SV

◦ about 4 to 6 L/min at rest

◦ a RBC leaving the left ventricle will arrive back at the left ventricle in about 1 minute

◦ vigorous exercise increases CO to 21 L/min for fit person and up to 35 L/min for world class athlete

Heart RateHeart Ratepulse – surge of pressure produced by each heart

beat that can be felt by palpating a superficial artery with the fingertips◦ infants have HR of 120 bpm or more

◦ young adult females avg. 72 - 80 bpm

◦ young adult males avg. 64 to 72 bpm

◦ heart rate rises again in the elderly

tachycardia - resting adult heart rate above 100 bpm◦ stress, anxiety, drugs, heart disease, or fever

◦ loss of blood or damage to myocardium

bradycardia - resting adult heart rate of less than 60 bpm◦ in sleep, low body temperature, and endurance trained athletes

Stroke Volume (SV)Stroke Volume (SV) the other factor that in cardiac output,

besides heart rate, is stroke volume

three variables govern stroke volume:1. preload2. contractility 3. afterload

example◦ increased preload or contractility causes

increases stroke volume◦ increased afterload causes decrease

stroke volume

PreloadPreloadpreload – the amount of tension in

ventricular myocardium immediately before it begins to contract◦ increased preload causes increased force of contraction◦ exercise increases venous return and stretches

myocardium◦ cardiocytes generate more tension during contraction◦ increased cardiac output matches increased venous

return

Frank-Starling law of heart - SV EDV◦ stroke volume is proportional to the end diastolic volume◦ ventricles eject as much blood as they receive◦ the more they are stretched, the harder they contract

AfterloadAfterloadafterload – the blood pressure in the aorta

and pulmonary trunk immediately distal to the semilunar valves◦ opposes the opening of these valves◦ limits stroke volume

hypertension increases afterload and opposes ventricular ejection

anything that impedes arterial circulation can also increase afterload◦ lung diseases that restrict pulmonary

circulation◦ cor pulmonale – right ventricular failure due to

obstructed pulmonary circulation in emphysema, chronic bronchitis, and black lung disease

Exercise and Cardiac Exercise and Cardiac OutputOutputexercise makes the heart work harder and increases

cardiac outputproprioceptors signal cardiac center

◦ at beginning of exercise, signals from joints and muscles reach the cardiac center of brain

◦ sympathetic output from cardiac center increases cardiac output

increased muscular activity increases venous return◦ increases preload and ultimately cardiac output

increase in heart rate and stroke volume cause an increase in cardiac output

exercise produces ventricular hypertrophy◦ increased stroke volume allows heart to beat more slowly at

rest

◦ athletes with increased cardiac reserve can tolerate more exertion than a sedentary person

Control of the Heart RateControl of the Heart Rate

Influences that allow heart to meet changing needs rapidly

Autonomic nervous system (ANS)Sympathetic nervous systemParasympathetic system

◦Cranial nerve X

Heart DiseaseHeart Disease

Most common cause of death in industrialized countries is heart and circulatory system disease

Classifications of Heart Classifications of Heart DiseaseDiseaseAnatomical classification

◦Endocarditis◦Myocarditis◦Pericarditis

Causative factors classification◦Congenital heart disease (present at birth)

◦Rheumatic heart disease◦Coronary artery disease◦Heart failure

Congenital Heart DiseaseCongenital Heart Disease

Congenital heart disease often results from fetal development defects

Atrial septal defect

Patent (open) ductus arteriosus

Ventricular septal defect

Coarctation of the aorta

Tetralogy of Fallot

Atrial Septal DefectAtrial Septal Defect

An atrial septal defect (ASD) is an abnormal opening in the interatrial septum.

Ventricular Septal Ventricular Septal DefectDefect

abnormal opening in the interventricular septum

Patent (open) Ductus Arteriosus

Patent ductus arteriosus (PDA) is a condition in which a blood vessel called the ductus arteriosus fails to close normally in an infant soon after birth

a congenital defect that occurs when the aorta narrows or becomes pinched.

Coarctation of the Aorta

Tetralogy of Fallot

a congenital heart disease that includes 4 specific defects: A large ventricular septal defect (VSD), 2) Pulmonary (PULL-mon-ary) stenosis, 3) Right ventricular hypertrophy (hi-PER-tro-fe) , 4) An overriding aorta

Rheumatic Heart DiseaseRheumatic Heart DiseaseStreptococci release toxins

during infection

Antibodies that combat toxin also attack heart valves

Heart valves become inflamed

Valve cusps thicken and harden

Pulmonary congestion occurs

Coronary Artery DiseaseCoronary Artery DiseaseNarrowing or blockage of the

vessels that supply the heart muscle causes coronary artery disease.

Coronary Artery DiseaseCoronary Artery DiseaseCoronary arteries can degenerate

Myocardial infarction

◦Creatine kinase released upon any muscle damage. Tests for certain forms of CK indicate whether an MI occurred.

Angina pectoris

Abnormalities of heart rhythm

Treatment of heart attacks

Heart FailureHeart Failure

Heart is unable to pump sufficient blood

Heart chambers enlarge

Blood backs up into lungs

Ventricular muscles have decreased ability

Fluid accumulates in lungs, liver, abdomen, legs

The Heart in the ElderlyThe Heart in the ElderlyHow the heart can ageHeart shrinksDecreased contraction strengthValves become less flexibleMurmur developsCardiac output decreasesAbnormal rhythmsHeart block

Prevention of Heart Prevention of Heart DiseaseDiseaseRisk factors that

cannot be modified◦Age◦Gender◦Heredity◦Body type

Risk factors that can be modified◦Smoking◦Physical

inactivity◦Weight◦Diet◦Blood pressure◦Diabetes, gout

Heart StudiesHeart StudiesStethoscope

Electrocardiograph (ECG or EKG)

◦Electrodes

Catheterization

◦Fluoroscope

Echocardiography (ultrasound cardiography)

◦Oscilloscope

Treatment of Heart Treatment of Heart DiseaseDiseaseMedical approaches

Surgical approaches

Combined approaches

MedicationsMedicationsDigitalis

Nitroglycerin

Beta-adrenergic blocking agents (beta-blockers)

Antiarrhythmic agents

Slow calcium-channel blockers

Anticoagulants

◦Aspirin

Correction of ArrhythmiasCorrection of ArrhythmiasArtificial pacemaker

◦Set rate

◦Only when heart skips beat

◦Adjustable pacing rate

Implantable cardioverter-defibrillator (ICD)

Heart SurgeryHeart Surgery

Coronary artery bypass graft (CSBG)

Angioplasty

Valve replacement

Surgical transplantation of heart or heart and lungs

Artificial heart

End of PresentationEnd of Presentation