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Biology 232
Human Anatomy and Physiology
Chapter 20 Lecture Outline
CARDIOVASCULAR SYSTEM – HEART
cardiology – study of the heart and associated diseases
Function of the Heart
pump – circulates blood in blood vessels
resting rate 75 beats/minute
circulates entire blood volume each minute
dual circulation
pulmonary circuit – deoxygenated (blue) blood from tissues  right
heart  lungs for oxygenation  left heart
systemic circuit – oxygenated (red) blood from pulmonary circuit  left
heart  body tissues  right heart
External Anatomy of Heart
size and shape similar to a fist (roughly cone-shaped)
apex – narrow end
base – major blood vessels emerge
lies in thoracic cavity within the mediastinum
rests on diaphragm
apex points to the left
pericardial sac (pericardium) – membrane surrounding heart
2 layers:
fibrous pericardium – outer dense irregular connective tissue
protects heart, prevents overstretching
anchored to diaphragm
serous pericardium – thin membrane, secretes pericardial fluid
parietal pericardium – lines inner fibrous pericardium
visceral pericardium (epicardium) – lines heart
pericardial cavity – space between parietal and visceral layers
lubricated with pericardial fluid
Internal Anatomy of Heart
3 layers of heart wall:
epicardium – outermost; visceral pericardium
mesothelium + connective tissue
myocardium – middle layer
cardiac muscle
endocardium – innermost; thin, smooth layer
endothelium + connective tissue
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Chambers of Heart – compartments within heart
2 atria – thin-walled chambers at base of heart
right atrium, left atrium
auricles – extensions of atria
2 ventricles – thick-walled chambers forming apex of heart
right ventricle, left ventricle
septa – walls separating the different chambers
interatrial septum – between right and left atria
interventricular septum – between right and left ventricles
right side of heart is completely separated from left
side of heart
atrioventricular septum – between atria and ventricles
atrioventricular (AV) valves – gates between atria
and ventricles
sulci – superficial grooves between heart chambers; contain adipose
tissue and blood vessels supplying the heart
coronary sulcus – between atria and ventricles
anterior and posterior interventricular sulci – between right
and left ventricles
Right Heart (pulmonary circuit) – receives deoxygenated blood from tissues and
pumps it to the lungs
Right atrium – receives deoxygenated blood from tissues
superior and inferior vena cava – large veins from body tissues
coronary sinus – venous sinus from heart tissue
right auricle – increases volume of right atrium
pectinate muscles – muscle ridges in anterior wall
right atrium contracts
Right AV valve (tricuspid valve) – blood flows through from right atrium to
right ventricle
3 cusps (flaps) – connected to tendon-like chordae tendineae
Right ventricle
trabeculae carneae – raised bundles of muscle fibers in wall
papillary muscles – cone-shaped trabeculae carneae
attach to chordae tendineae
right ventricle contracts
Pulmonary valve (semilunar valve) – blood flows through into pulmonary trunk
 right and left pulmonary arteries  pulmonary capillaries 
pulmonary veins  left heart
(pulmonary arteries contain deoxygenated blood)
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Left Heart (systemic circuit) – receives oxygenated blood from lungs and pumps to
body tissues
Left atrium – receives oxygenated blood from pulmonary circuit
4 pulmonary veins carry oxygenated blood returning from lungs
left auricle – increases volume of left atrium
no pectinate muscles
left atrium contracts
Left AV valve (mitral valve or bicuspid valve) – blood flows through from left
atrium to left ventricle
2 cusps – chordae tendineae
Left ventricle
thickest myocardial wall
trabeculae carneae – papillary muscles
left ventricle contracts
Aortic valve (semilunar valve) – blood flows through into ascending aorta 
aortic arch  descending aorta  arterial branches to all tissues 
systemic capillaries  systemic veins  right heart
Fibrous Skeleton of Heart
dense fibrous connective tissue rings surround heart valves
continuous with dense fibrous connective tissue in atrioventricular septum
functions:
supports valves
attachment site for cardiac muscle
electrical insulation between atria and ventricles
Function of Heart Valves
one-way valves
open and close due to pressure changes as heart contracts
blood always flows from high pressure to low pressure
AV valves (tricuspid and bicuspid)
cusps connected to papillary muscles in ventricles
low ventricular pressure – when ventricles are relaxed
blood flows through open valve into ventricles
high ventricular pressure – when ventricles are contracting
AV valves close
blood pushes cusps toward atria
papillary muscles and chordae tendineae prevent backflow
Semilunar valves (aortic and pulmonary valves)
3 cusps - crescent moon-shaped (form convex-concave shape)
high ventricular pressure – when ventricles are contracted
semilunar valves open
blood flows into aorta and pulmonary trunk
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low ventricular pressure – when ventricles relax
semilunar valves close
blood in aorta and pulmonary trunk flows back towards ventricles
filling concave cusps and pushing them closed
valvular incompetence – valve doesn’t close completely
regurgitation – blood leaks backwards
valvular stenosis – narrowing of valve, doesn’t open fully
heart murmurs – abnormal sounds due to turbulence caused by faulty valves
Cardiac Muscle Function
branched fibers, one nucleus, many large mitochondria
striated – thick and thin filaments overlap to form different bands
sarcomeres contract when action potential causes calcium ions to flow into
cytoplasm from SR
calcium also enters from interstitial space
intercalated discs – connect neighboring muscle cells
gap junctions allow action potential to conduct between cells
Autorhythmicity – electrical stimulation comes from specialized cardiac muscle
fibers
autorhythmic fibers – 1% of cardiac muscle fibers
spontaneously depolarize at regular intervals (leak ions)
pacemaker – sets rhythm for contractions (depolarizes fastest)
conduction system – pathway for propagation of pacemaker signal
ensures coordinated contractions
Conduction Pathway
1) sinoatrial (SA) node – normal pacemaker in right atrial wall
resting potential is not stable – spontaneously reaches threshold
100 times/minute
threshold depolarization produces an action potential
action potential propagates through both atrial walls via gap
junctions
2) atrioventricular (AV) node – in atrial septum
3) atrioventricular (AV) bundle (bundle of His)
only site for conduction from atria to ventricles
4) right and left bundle branches – in interventricular septum
conduct impulse to apex of heart
5) Purkinje fibers – conduct impulse from apex upward throughout
ventricular walls
AV node can act as a pacemaker (40-60 impulses/minute)
other autorhythmic fibers fire even more slowly
ectopic pacemaker – abnormal site depolarizes rapidly
caffeine, nicotine, electrolyte imbalances, hypoxia
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Cardiac Muscle Action Potential
1) depolarization
resting membrane potential is -90mV
conduction pathway causes threshold depolarization
voltage-gated fast sodium channels open
sodium ions rush in – rapid depolarization
sodium channels close
2) plateau – maintained depolarization
voltage-gated slow calcium channels open – calcium ions
flow in from SR and interstitial space
calcium inflow balances potassium outflow and delays
repolarization
3) repolarization
Ca channels close
voltage-gated slow potassium channels open – potassium ions rush
out and restore resting membrane potential
long refractory period – another contraction cannot occur until relaxation
has occurred (prevents tetanus)
contraction is like skeletal muscle
calcium ions bind to troponin
actin and myosin filaments bind and slide past each other
Electrocardiogram (ECG or EKG) – composite recording of action potentials
generated by the heart
measured on body surface by electrodes in specific locations
normal sinus rhythm – generated by sinoatrial node
P wave – atrial depolarization
QRS complex – ventricular depolarization
T wave – ventricular repolarization
(atrial repolarization is masked by QRS)
size of waves and intervals between them can indicate condition
of the heart
Cardiac Cycle – time between 1 heartbeat and the next
systole – phase of contraction
atrial systole – atria contract together (follows P wave)
ventricular systole – ventricles contract together (follows QRS complex)
diastole – phase of relaxation
atrial diastole – atria relax (during QRS)
ventricular diastole – ventricles relax (follows T wave)
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1 Cardiac Cycle:
atrial systole – atria contract
pressure increases in atria
blood flows through open AV valves into relaxed ventricles
end-diastolic volume – volume in ventricles (130ml)
ventricular systole – ventricles contract
(simultaneous atrial diastole – atria relax)
pressure increases in ventricles
AV valves close
isovolumetric contraction – pressure in ventricle increases but volume
stays the same until pressure is greater than pressure in aorta or
pulmonary trunk
semilunar valves open
ventricular ejection – ventricles continue to contract
blood flows into aorta/pulmonary trunk
(70-80ml ejected – remaining 50-60ml is end-systolic volume)
ventricular diastole – ventricles relax
pressure decreases in ventricles
when ventricular pressure is less than aortic/pulmonary trunk pressure
semilunar valves close
isovolumetric relaxation – pressure in ventricle decreases but volume stays
the same until pressure is less than atrial pressure
AV valves open – ventricular filling begins
Blood Pressure – pressure in systemic circulation (pulmonary pressure is lower)
systolic pressure – due to maximum left ventricular contraction
120mmHg
diastolic pressure – during ventricular relaxation, pressure maintained
by smooth muscle in arteries; 80mmHg
Heart Sounds – auscultation with stethoscope
due to turbulence of blood as valves close
2 audible sounds:
S1 (lubb) – louder and longer
closing of AV valves
S2 (dupp) – softer and shorter
closing of semilunar valves
murmurs – abnormal sounds (valve disorders, septal defects)
Fetal Circulation
placenta – umbilical artery and vein
2 shunts – by-pass lungs
foramen ovale – hole between right and left atria
fossa ovalis – closed following birth
ductus arteriosus – connection from pulmonary trunk to aorta
ligamentum arteriosum – closed following birth
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CARDIODYNAMICS
Cardiac Output (CO) - volume of blood ejected by each ventricle/minute
(equal for right and left ventricles)
CO = stroke volume X heart rate
stroke volume (SV) – ml of blood ejected by each ventricle/cardiac cycle
SV = end-diastolic volume(EDV) – end-systolic volume(ESV)
at rest 130ml – 60ml = 70ml stroke volume
heart rate (HR) – heart beats/minute (75 bpm)
CO at rest
70ml/beat X 75 beats/min = 5.25 liters/minute
CO changes to meet body needs
cardiac reserve – difference between maximum cardiac output and resting
cardiac output
normally 4-5 times resting CO
Increasing Cardiac Output
Increase stroke volume
3 factors affect SV:
1) preload – stretch (fullness) of ventricle before contraction
>EDV = >preload = stronger contraction
pericardial sac prevents overstretching heart muscle
EDV affected by filling time and venous return
(equalizes CO of right and left ventricles)
2) contractility
positive inotropic agents – increase contractility
most increase Ca entering cardiac muscle cells
sympathetic NS, epinephrine, thyroid hormone,
glucagon, digitalis, Ca ions
negative inotropic agents – decrease contractility
parasympathetic NS, calcium channel blockers,
beta-blockers (block sympathetic response)
3) afterload – pressure in aorta/pulmonary trunk
resists ejection of blood from ventricles
high blood pressure and atherosclerosis decrease SV
Increase heart rate – up to 160-180 bpm
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Regulation of Heart Rate
pacemaker - SA node 100 beats/minute
normal resting rate – 70-80 bpm
HR depends on:
tissue demands – basal metabolic rate and activity level
stroke volume – as SV decreases HR must increase
Autonomic Nervous System
cardiovascular center – medulla oblongata
inputs – higher brain, limbic system (eg. fear, excitement)
sensory – proprioceptors – physical activity
chemoreceptors – oxygen, carbon dioxide levels
baroreceptors – blood pressure (aorta, carotid)
output – sympathetic (norepinephrine)
cardiac accelerator nerves – beta 1 receptors
SA and AV nodes – increase firing rates
output – parasympathetic (acetylcholine)
vagus nerves
SA and AV nodes - decrease firing rates
predominates at rest
Chemical Regulation
hormones
adrenal medulla (sympathetic) – epinephrine, norepinephrine
thyroid hormone – increases heart rate
Other Factors Affecting Heart Rate
age – faster HR in babies and elderly
body temperature
high (hyperthermia) – faster HR
low (hypothermia) – slower HR
fitness – decreases HR
electrolyte levels
Na and K decrease HR
Ca increases HR
tachycardia – high resting heart rate (>100bpm)
bradycardia – low resting heart rate (<60bpm)
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