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Chapter 15
Cardiovascular System
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Size of Heart
Average Size of Heart
• 14 cm long
• 9 cm wide
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Heart
• Hollow, fist-sized muscular
organ
• Located slightly to left of
body’s midline
• Acts as dual pumping system
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Location of Heart
• posterior to sternum
• medial to lungs
• anterior to vertebral column
• base lies beneath 2nd rib
• apex at 5th intercostal space
• lies upon diaphragm
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Coverings of Heart
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Pericardium
• Fibrous sac that covers heart
–2 portions
–Fibrous pericardium-external sac
• Tough, white, fibrous tissue; fits
loosely around heart
• Protects heart & serous membrane
–Serous pericardium: internal sac
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Serous Layer
• Serous layer - a smooth inner sac with
lubricated surfaces which allow movement
– parietal layer - lines the inner surface of
the fibrous pericardium
– visceral layer - covers the entire surface
of the heart
• The potential space between the parietal
and visceral layers of the serous
pericardium is the pericardial cavity.
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Heart Wall: Layers
•Endocardium
•Myocardium
• Epicardium
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Wall of the Heart
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Wall of the Heart
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Heart Chambers
Right Atrium
• receives blood from
• inferior vena cava
• superior vena cava
• coronary sinus
Right Ventricle
• receives blood from
right atrium
Left Atrium
• receives blood from
pulmonary veins
Left Ventricle
• receives blood from
left atrium
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Heart Valves
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Coronal Sections of Heart
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Heart Valves
Tricuspid Valve
Pulmonary and Aortic Valve
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Skeleton of Heart
• fibrous rings to which the heart valves are attached
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Path of Blood
Through the Heart
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Path of Blood
Through the Heart
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Blood Supply to Heart
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Blood Supply to Heart
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Angiogram of Coronary Arteries
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Heart Actions
Atrial Systole/Ventricular Diastole
Atrial Diastole/Ventricular Systole
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Cardiac Cycle
Atrial Systole/Ventricular Diastole
• blood flows passively into ventricles
• remaining 30% of blood pushed into ventricles
• A-V valves open/semilunar valves close
• ventricles relaxed
• ventricular pressure increases
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Cardiac Cycle
Ventricular Systole/Atrial diastole
• A-V valves close
• chordae tendinae prevent cusps of valves from
bulging too far into atria
• atria relaxed
• blood flows into atria
• ventricular pressure increases and opens semilunar
valves
• blood flows into pulmonary trunk and aorta
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Heart Sounds
Lubb
• first heart sound
• occurs during ventricular systole
• A-V valves closing
Dupp
• second heart sound
• occurs during ventricular diastole
• pulmonary and aortic semilunar valves closing
Murmur – abnormal heart sound
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Heart Sounds
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Cardiac Conduction System
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Cardiac Conduction & Control
• Intrinsic: internally generated
control
• Extrinsic: control from outside heart
• Heart rate controlled by both
– A.N.S.: can fine tune heart
– S.N.S.-can accelerate heart rate
– P.S.-can slow heart rate
– Hormones-can influence heart rate ex.
epinephrine
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Intrinsic Control
• Sinoatrial node (S.A)
• Atrioventricular Node (A.V.)
• Bundle of His
• Purkinje Fibers
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Sinoatrial Node
• The natural pacemaker of the heart
• Location - junction of superior vena cava and
right atrium
• Impulse for contraction begins at the SA node
and are conducted to the AV node by atrial
mycardial fibers (internodal tracts)
• The SA node is supplied by both divisions of the
ANS
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Atrioventricular Node
• Located in lower right
interatrial septum
• Impulse slows
• Slowing allows atria to
contract & ventricle to fill
with blood
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Bundle of His
• Originates in AV. Node
• Divides into left and right
branches
• Impulse from AV. Continues
into left and right bundle
branches
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Purkinje Fibers
• Connect bundle branches to lateral
walls of ventricle
• Impulse moves through Purkinje fibers
reaching ventricle muscles
• Stimulation of ventricle muscles begins
in intraventricular septum & moves
downward
• Depolarization of ventricles &
contraction
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Cardiac Conduction System
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Electrocardiogram
• recording of electrical changes that occur in the myocardium
• used to assess heart’s ability to conduct impulses
P wave – atrial depolarization
QRS wave – ventricular depolarization
T wave – ventricular repolarization
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Electrocardiogram
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Electrocardiogram
A prolonged QRS complex may result from damage to the A-V
bundle fibers
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Cardiac Cycle
52
Clinical Application
Arrhythmias
Ventricular fibrillation
• rapid, uncoordinated
depolarization of ventricles
Tachycardia
• rapid heartbeat
Atrial flutter
• rapid rate of atrial
depolarization
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Regulation of Cardiac Cycle
Autonomic nerve impulses alter the
activities of the S-A and A-V nodes
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Regulation of Cardiac Cycle
Additional Factors that Influence HR
• physical exercise
• body temperature
• concentration of various ions
• potassium
• calcium
• parasympathetic impulses decrease heart action
• sympathetic impulses increase heart action
• cardiac center regulates autonomic impulses to the heart
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Blood Vessels
• arteries
• carry blood away from ventricles of heart
• arterioles
• receive blood from arteries
• carry blood to capillaries
• capillaries
• sites of exchange of substances between
blood and body cells
• venules
• receive blood from capillaries
• veins
• carry blood toward ventricle of heart
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Arteries
Artery
• thick strong wall
• endothelial lining
• middle layer of smooth
muscle and elastic tissue
• outer layer of connective
tissue
• Carry blood away from
heart
•Vascular resistance low
•Mean arterial pressure =
100mmHg
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Arterioles
Arterioles
• thinner wall than artery
• endothelial lining
• some smooth muscle
tissue
• small amount of
connective tissue
• helps control blood flow
into a capillary
• Mean pressure =85mmHg
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Arteriole
• smallest arterioles only have a few smooth muscle fibers
• capillaries lack muscle fibers
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Venules
Venule
• thinner wall than arteriole
• less smooth muscle and elastic tissue than arteriole
•Carry blood away from capillaries to veins
•BP 15mmHg when blood returning to heart
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Veins
Vein
• thinner wall than artery
• three layers to wall but middle layer is poorly developed
• serves as blood reservoir
•Carry blood from venules to heart
• have valves =prevent backflow of blood
•Mean pressure =less than 15mmHg
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Walls of Artery and Vein
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Capillaries
• smallest diameter blood vessels
• extensions of inner lining of arterioles
• walls are endothelium only; single layer
• semipermeable
• sinusoids – leaky capillaries
•Join arterioles & venules
•Vascular resistance low = 35mmHg
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Capillary Network
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Exchange in the Capillaries
• water and other substances leave capillaries because of net outward pressure
at the capillaries’ arteriolar ends
• water enters capillaries’ venular ends because of a net inward pressure
• substances move in and out along the length of the capillaries according to
their respective concentration gradients
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Venous Valves
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Characteristics of Blood Vessels
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Blood Volumes in Vessels
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Arterial Blood Pressure
Blood Pressure – force the blood exerts against the
inner walls of the blood vessels
Arterial Blood Pressure
• rises when ventricles contract
• falls when ventricles relax
• systolic pressure – maximum pressure
• diastolic pressure – minimum pressure
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Pulse
• alternate expanding and recoiling of the arterial wall
that can be felt
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Factors That Influence
Arterial Blood Pressure
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Control of Blood Pressure
Controlling cardiac output and peripheral resistance
regulates blood pressure
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Control of Blood Pressure
If blood pressure rises, baroreceptors initiate the
cardioinhibitory reflex, which lowers the blood pressure
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Control of Blood Pressure
Dilating arterioles helps regulate blood pressure
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Venous Blood Flow
• not a direct result of heart
action
• dependent on
• skeletal muscle
contraction
• breathing
• venoconstriction
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Pulmonary Circuit
• consists of vessels that carry blood from the heart to the lungs
and back to the heart
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Blood Flow Through Alveoli
• cells of alveolar wall are tightly joined together
• the high osmotic pressure of the interstitial fluid draws
water out of them
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Systemic Circuit
• composed
of vessels that lead from the
heart to all body parts (except the lungs)
and back to the heart
• includes the aorta and its branches
• includes the system of veins that return
blood to the right atrium
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Major Vessels of Arterial System
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Abdominal Aorta and Its Major
Branches
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Arteries to Neck, Head, and
Brain
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Cerebral Arterial Circle
• Circle of Willis
• formed by anterior and posterior cerebral arteries, which
join the internal carotid arteries
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Arteries to Shoulder
and Upper Limb
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Arteries to the Lower Limb
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Major Vessels of the Venous
System
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Major Veins of the Brain, Head
and Neck
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Veins from the Upper Limb and
Shoulder
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Veins That Drain the Thoracic
Wall
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Veins That Drain the Abdominal
Viscera
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Veins of the Lower Limb and
Pelvis
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Life-Span Changes
• cholesterol deposition in blood vessels
• heart enlargement
• death of cardiac muscle cells
• increase in fibrous connective tissue of the heart
• increase in adipose tissue of the heart
• increase in blood pressure
• decrease in resting heart rate
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