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The Cardiovascular system: 15
Heart
Unit 1
Chapter 15
Location
15
• Thoracic cavity between two lungs
~2/3 to left of midline
• surrounded by pericardium:
• Fibrous pericardium-
• Inside is serous pericardium- double
layer around heart
Parietal layer fused to fibrous pericardium
Inner visceral layer adheres tightly to heart
Filled with pericardial fluid- reduces friction
during beat.
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Inelastic and anchors heart in place
Figure 15.1
Heart Wall
15
Two separate networks via gap junctions
in intercalated discs- atrial &
ventricular
Networks- contract as a unit
• Endocardium- Squamous epithelium
lines inside of myocardium
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• Epicardium- outer layer
• Myocardium- cardiac muscle
Figure 15.2a
Figure 15.2b
Figure 15.2c
Chambers
15
• 4 chambers
• 2 upper chambers= Atria
Between is interatrial septum
Contains fossa ovalis- remnant of foramen ovalis
• 2 lower chambers = ventricles
• Wall thickness depends on work load
Atria thinnest
Right ventricle pumps to lungs & thinner than left
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Between is interventricular septum
Great Vessels Of Heart- Right
15
• Superior & inferior Vena Cavae
• R. Atrium  R. Ventricle
• pumps through Pulmonary Trunk
• R & L pulmonary arteries
•  lungs
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Delivers deoxygenated blood to R. atrium
from body
Coronary sinus drains heart muscle veins
Great Vessels Of Heart-Left
15
• Pulmonary Veins from lungs
• L. atrium Left ventricle
• ascending aorta body
• Between pulmonary trunk & aortic
arch is ligamentum arteriosum
• fetal ductus arteriosum remnant
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oxygenated blood
Figure 15.3a
Figure 15.3b
Figure 15.3c
Valves
15
• Designed to prevent back flow in
response to pressure changes
• Atrioventricular (AV) valves
• Right = tricuspid valve (3 cusps)
• Left = bicuspid or mitral valve
• Semilunar valves near origin of aorta &
pulmonary trunk
• Aortic & pulmonary valves respectively
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Between atria and ventricles
Figure 15.4ab
Figure 15.4c
Figure 15.4d
Figure 15.5a
Figure 15.5b
Blood Supply Of Heart
15
• Blood flow through vessels in
myocardium = coronary circulation
• L. & Right coronary arteries
• Deoxygenated blood collected by
Coronary Sinus (posterior)
• Empties into R. Atrium
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branch from aorta
branch to carry blood throughout muscle
• 1% of cardiac muscle generate action
potentials= Pacemaker & Conduction
system
• Normally begins at sinoatrial (SA) node
• Atria & atria contract
• AV node -slows
• AV bundle (Bundle of His)
• bundle branches Purkinje fibers
•  apex and up- then ventricles contract
15
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Conduction System
• Depolarize spontaneously
• sinoatrial node ~100times /min
• also AV node ~40-60 times/min
• in ventricle ~20-35 /min
• Fastest one run runs the heart =
pacemaker
• Normally the sinoatrial node
15
Unit 1
Pacemaker
Figure 15.6
Electrocardiogram
15
• Recording of currents from cardiac
conduction on skin = electrocardiogram
(EKG or ECG)
• P wave= atrial depolarization
• QRS complex= Ventricular depolarization
Contraction of ventricle
• T-wave = ventricular repolarization
Just after ventricles relax
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Contraction begins right after peak
Repolarization is masked in QRS
Figure 15.7
Cardiac Cycle
15
• after T-wave ventricular diastole
Ventricular pressure drops below atrial & AV
valves open  ventricular filling occurs
• After P-wave atrial systole
Finishes filling ventricle (`25%)
Pressure pushes AV valves closed
Pushes semilunar valves open and ejection occurs
Ejection until ventricle relaxes enough for arterial
pressure to close semilunar valves
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• After QRS ventricular systole
• Review muscle
• Heart has addition of External Ca2+
• creates a plateau
• prolonged depolarized period.
• Can not go into tetanus.
15
Unit 1
Action Potential
Figure 15.8
• Cardiac Output (CO) = liters/min
pumped
• Heart Rate (HR) = beats/minute
(bpm)
• Stroke volume (SV) = volume/beat
•
CO = HR x SV
15
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Flow Terms
Controls- Stroke Volume (S.V.)
15
• Degree of stretch = Frank-Starling law
• increased sympathetic activity
• High back pressure in artery 
decreased S.V.
Slows semilunar valve opening
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Increase diastolic Volume increases
strength of contraction increased S.V.
Increased venous return  increased S.V.
Controls- Heart Rate
15
• Pacemaker adjusted by nerves
Cardiovascular center in Medulla
• parasympathetic- ACh slows
• Sympathetic - norepinephrine speeds
• Sensory input for control:
baroreceptors (aortic arch & carotid sinus)- B.P.
Chemoreceptors- O2, CO2, pH
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Via vagus nerve
Other Controls
15
• Hormones:
Epinephrine & norepinephrine increase H.R.
Thyroid hormones stimulate H.R.
Called tachycardia
Increased Na+ or K+ decrease H.R. &
contraction force
Increased Ca2+ increases H.R. & contraction
force
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• Ions
Figure 15.9
• Aerobic exercise (longer than 20
min) strengthens cardiovascular
system
• Well trained athlete doubles
maximum C.O.
• Resting C.O. about the same but
resting H.R. decreased
15
Unit 1
Exercise
Figure 15.10