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The Circulatory System
The Heart
Anatomy & Physiology II
Chapter 14
Circulatory System: The Heart

cardiology – the scientific study of the heart and
the treatment of its disorders

cardiovascular 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 Heart
Circulation
 Continuous one-way circuit of the blood
vessels
 Propelled by heart
Cardiovascular System Circuit
CO2
O2

◦ fully oxygenated blood
arrives from lungs via
pulmonary veins
◦ blood sent to all organs of
the body via aorta
Pulmonary circuit
O2-poor,
CO2-rich
blood
O2-rich,
CO2-poor
blood
Systemic circuit
CO2
O2
left side of heart

right side of heart
◦ lesser oxygenated blood
arrives from inferior and
superior vena cava
◦ blood sent to lungs via
pulmonary trunk
Location of the Heart
Between the lungs
 Left of the midline of the body
 In mediastinum
 Apex pointed toward left

Position, Size, and Shape

heart located in
mediastinum, between
lungs
Aorta

base – wide, superior
portion of heart, blood
vessels attach here

apex - inferior end, tilts to
the left, tapers to point

weighs 10 oz.
Superior
vena cava
Right lung
Pulmonary
trunk
Base of
heart
Parietal
pleura (cut)
Pericardial
sac (cut)
Apex
of heart
Diaphragm
Heart Wall

epicardium (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 vessels

myocardium
◦ 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 Heart Wall and Pericardium
The serous
pericardium
covers the
heart and
lines the
fibrous
pericardium.
ZOOMING IN
• Which layer of
the heart wall is
the thickest?
Pericardium (pericardial 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 Heart Wall
Pericardial
cavity
Pericardial
sac:
Fibrous
layer
Serous
layer
Epicardium
Myocardium
Endocardium
Epicardium
Pericardial sac
Special Features of the Myocardium
Cardiac muscles

Are lightly striated (striped)

Have single nucleus cells

Are controlled involuntarily

Have intercalated disks

Have branching muscle fibers
Divisions 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 Chambers
Right 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 Heart as a Double Pump
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 and Great Vessels
ZOOMING IN
• Which heart
chamber has
the thickest
wall?
Blood Flow Through Heart
10
1 Blood enters right atrium from superior
and inferior venae cavae.
Aorta
Left pulmonary
artery
11
5
5
9
Pulmonary trunk
Superior
vena cava
Right
pulmonary
veins
4
6
6
Left pulmonary
veins
Left atrium
1
Aortic valve
7
3
Right
atrium
8
2
Right AV
(tricuspid) valve
Left ventricle
3 Contraction of right ventricle forces
pulmonary valve open.
4 Blood flows through pulmonary valve
into pulmonary trunk.
5 Blood is distributed by right and left
pulmonary arteries to the lungs, where it
unloads CO2 and loads O2.
6 Blood returns from lungs via pulmonary
veins to left atrium.
7 Blood in left atrium flows through left AV
valve into left ventricle.
8 Contraction of left ventricle (simultaneous with
step 3 ) forces aortic valve open.
9 Blood flows through aortic valve into
ascending aorta.
Right
ventricle
Inferior
vena cava
Left AV
(bicuspid) valve
2 Blood in right atrium flows through right
AV valve into right ventricle.
11
10 Blood in aorta is distributed to every organ in
the body, where it unloads O2 and loads CO2.
11 Blood returns to heart via venae cavae.
blood pathway travels from the right atrium through the body
and back to the starting point
Four Valves

Valves 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 Valves

atrioventricular (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 Valves
Left AV
(bicuspid) valve
Right AV
(tricuspid) valve
Fibrous
skeleton
Openings to
coronary arteries
Aortic
valve
Pulmonary
valve
Blood Supply to the Myocardium
Coronary circulation
 Right coronary artery
 Left coronary artery
 Coronary sinus
Coronary 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 - Posterior
Aorta
Left pulmonary
artery
Superior
vena cava
Right pulmonary
artery
Left pulmonary
veins
Right pulmonary
veins
Left atrium
Coronary sulcus
Right atrium
Coronary sinus
Inferior vena cava
Fat
Posterior
interventricular
sulcus
Left ventricle
Apex of heart
Right ventricle
Posterior view
Opening of coronary arteries in the
aortic valve (anterior view).
(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.
Coronary Blood Flow
blood 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
Angina

angina 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 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 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 System
Electrical energy stimulates heart muscle

Nodes
◦ 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 System
1 SA node fires.
Right atrium
2 Excitation spreads through
atrial myocardium.
2
1
Sinoatrial node
(pacemaker)
Left
atrium
2
Atrioventricular
node
Atrioventricular
bundle
Purkinje fibers
Purkinje
fibers
3
Bundle
branches
4
5
3 AV node fires.
4 Excitation spreads down AV
bundle.
5 Purkinje fibers distribute
excitation through
ventricular myocardium.
The Conduction Pathway
Sinus rhythm
 Sinoatrial (SA) node
 Atria
 Atrioventricular (AV) node
 Internodal pathways
 Bundle of His
 Bundle branches and Purkinje fibers
 Ventricles
Function 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 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
R
R
+1
Millivolts

PQ
ST
segment segment
T wave
P wave
0
PR
Q
interval
S
QT
interval
QRS interval
–1
Atria
contract
Ventricles
contract
Atria
contract
Ventricles
contract
EKG Deflections

P 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 (ECG)
0.8 second
R
R
+1
Millivolts
PQ
segment
ST
segment
T wave
P wave
0
PR
interval
Q
S
QT
interval
QRS interval
–1
Atria
contract
Ventricles
contract
Atria
contract
Ventricles
contract
Electrical Activity of Myocardium
1)
atrial depolarization begins
Key
2)
3)
atrial depolarization
complete (atria contracted)
ventricles begin to
depolarize at apex; atria
repolarize (atria relaxed)
Wave of
depolarization
Wave of
repolarization
R
P
P
Q
S
4
1 Atria begin depolarizing.
R
ventricular depolarization
complete (ventricles
contracted)
Q
S
2
5
Atrial depolarization complete.
Ventricular repolarization begins at apex
and progresses superiorly.
R
R
5)
ventricles begin to
repolarize at apex
ventricular repolarization
complete (ventricles
relaxed)
T
P
P
Q
3
6)
T
P
P
4)
Ventricular depolarization complete.
Ventricular depolarization begins at apex
and progresses superiorly as atria repolarize.
Q
S
6
Ventricular repolarization complete; heart
is ready for the next cycle.
Diagnostic Value of ECG

abnormalities in conduction pathways

myocardial infarction

nodal damage

heart enlargement

electrolyte and hormone imbalances
ECGs: Normal and Abnormal
(a) Sinus rhythm (normal)
(b) Nodal rhythm—no SA node activity

abnormalities in
conduction pathways

myocardial infarction

heart enlargement

electrolyte and hormone
imbalances
Cardiac Cycle

cardiac 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 Cycle

in 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
The Cardiac Cycle
ZOOMING IN • When the ventricles contract, what valves
close? What valves open?
Ventricular Filling

during 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 Ejection

ejection 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 Changes
end-systolic volume (ESV)
-passively added to ventricle
during atrial diastole
-added by atrial systole
total: end-diastolic volume (EDV)
stroke volume (SV) ejected
by ventricular systole
60 ml
+30 ml
+40 ml
130 ml
leaves: end-systolic volume (ESV)
60 ml
-70 ml
both ventricles must eject same amount of blood
Unbalanced Ventricular Output
1
Right ventricular
output exceeds left
ventricular output.
2
Pressure backs up.
3
Fluid accumulates in
pulmonary tissue.
pulmonary edema
1
2
3
(a) Pulmonary edema
Unbalanced Ventricular Output
Left ventricular
output exceeds right
ventricular output.
2 Pressure backs up.
1
3 Fluid accumulates in
systemic tissue.
1
2
3
(b) Systemic edema
peripheral edema
Congestive Heart Failure

congestive 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) – the amount ejected by ventricle in
1 minute
cardiac 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)
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 Rate

pulse – 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)
the other factor that in cardiac output, besides
heart rate, is stroke volume


three variables govern stroke volume:
1. preload
2. contractility
3. afterload
example

◦
◦
increased preload or contractility causes increases
stroke volume
increased afterload causes decrease stroke volume
Preload

preload – 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
Afterload

afterload – 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 Output

exercise makes the heart work harder and increases
cardiac output

proprioceptors 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 Rate
Influences that allow heart to meet
changing needs rapidly
 Autonomic nervous system (ANS)
 Sympathetic nervous system
 Parasympathetic system
◦ Cranial nerve X
Heart Disease
Most common cause of death in
industrialized countries is heart and
circulatory system disease
Classifications of Heart Disease

Anatomical classification
◦ Endocarditis
◦ Myocarditis
◦ Pericarditis

Causative factors classification
◦ Congenital heart disease (present at birth)
◦ Rheumatic heart disease
◦ Coronary artery disease
◦ Heart failure
Congenital 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 Defect
An atrial septal defect (ASD) is an abnormal opening in the
interatrial septum.
Ventricular Septal Defect
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
Coarctation of the Aorta
a congenital defect that occurs when the aorta narrows or
becomes pinched.
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 Disease

Streptococci 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 Disease

Narrowing or blockage of the vessels that
supply the heart muscle causes coronary
artery disease.
Coronary Artery Disease
Coronary 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 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 Elderly
How the heart can age

Heart shrinks

Decreased contraction strength

Valves become less flexible

Murmur develops

Cardiac output decreases

Abnormal rhythms

Heart block
Prevention of Heart Disease

Risk 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 Studies

Stethoscope

Electrocardiograph (ECG or EKG)
◦ Electrodes

Catheterization
◦ Fluoroscope

Echocardiography (ultrasound cardiography)
◦ Oscilloscope
Treatment of Heart Disease

Medical approaches

Surgical approaches

Combined approaches
Medications

Digitalis

Nitroglycerin

Beta-adrenergic blocking agents (betablockers)

Antiarrhythmic agents

Slow calcium-channel blockers

Anticoagulants
◦ Aspirin
Correction of Arrhythmias

Artificial pacemaker
◦ Set rate
◦ Only when heart skips beat
◦ Adjustable pacing rate

Implantable cardioverter-defibrillator
(ICD)
Heart Surgery

Coronary artery bypass graft (CSBG)

Angioplasty

Valve replacement

Surgical transplantation of heart or heart
and lungs

Artificial heart
End of Presentation