The document summarizes key aspects of the cardiovascular system and the heart. It describes the location of the heart in the thoracic cavity surrounded by the pericardium. It outlines the structure of the heart including four chambers, cardiac muscle tissue, and the conduction system. It also summarizes the blood flow through the heart, how cardiac output is calculated, and how the heart rate and stroke volume are regulated.

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Chapter 15
The Cardiovascular System:
The Heart

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Location of the Heart
■ Thoracic cavity between two lungs
❑ ~2/3 to left of midline
■ surrounded by pericardium:
■ Fibrous pericardium -
❑ Inelastic and anchors heart in place
■ 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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Position of the Heart

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Position of the Heart

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Heart Wall
■ Epicardium - outer layer
■ Myocardium - cardiac muscle
❑ 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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Pericardium

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Cardiac Muscle Fibers

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Cardiac Muscle Tissue

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Chambers of the Heart
■ 4 chambers
■ 2 upper chambers = Atria
❑ Between is interatrial septum
❑ Contains fossa ovalis - remnant of foramen ovalis
■ 2 lower chambers = ventricles
❑ Between is interventricular septum
■ Wall thickness depends on work load
❑ Atria thinnest
❑ Right ventricle pumps to lungs & thinner than left

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Structure of the Heart

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Structure of the Heart

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Structure of the Heart

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Great Vessels Of Heart-Right
■ Superior & inferior Vena Cavae
❑ Delivers deoxygenated blood to R. atrium
from body
❑ Coronary sinus drains heart muscle veins
■ R. Atrium R. Ventricle
■ pumps through Pulmonary Trunk
■ R & L pulmonary arteries
■ lungs

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Posterior View of Heart

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Anterior View of Frontal Section

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Great Vessels Of Heart-Left
■ Pulmonary Veins from lungs
❑ oxygenated blood
■ L. atrium Left ventricle
■ ascending aorta body
■ Between pulmonary trunk & aortic arch is
ligamentum arteriosum
■ fetal ductus arteriosum remnant

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Valves
■ Designed to prevent back flow in response
to pressure changes
■ Atrioventricular (AV) valves
❑ Between atria and ventricles
■ 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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Atrioventricular Valves: Bicuspid
Valves

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Atrioventricular Valves: Superior
View

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Blood Flow
Through
Heart

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Blood Flow

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Blood Supply Of Heart
■ Blood flow through vessels in myocardium =
coronary circulation
■ Left & right coronary arteries
❑ branch from aorta
❑ branch to carry blood throughout muscle
■ Deoxygenated blood collected by coronary
sinus (posterior)
■ Empties into right atrium

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Conduction System
■ 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

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Pacemaker
■ 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

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Frontal plane
Right atrium
Right ventricle
Left atrium
Left ventricle
Anterior view of frontal section
Frontal plane
Left atrium
Left ventricle
Anterior view of frontal section
SINOATRIAL (SA) NODE
1
Right atrium
Right ventricle
Frontal plane
Left atrium
Left ventricle
Anterior view of frontal section
SINOATRIAL (SA) NODE
ATRIOVENTRICULAR
(AV) NODE
1
2
Right atrium
Right ventricle
Frontal plane
Left atrium
Left ventricle
Anterior view of frontal section
SINOATRIAL (SA) NODE
ATRIOVENTRICULAR
(AV) NODE
ATRIOVENTRICULAR (AV)
BUNDLE (BUNDLE OF HIS)
1
2
3
Right atrium
Right ventricle
Frontal plane
Left atrium
Left ventricle
Anterior view of frontal section
SINOATRIAL (SA) NODE
ATRIOVENTRICULAR
(AV) NODE
ATRIOVENTRICULAR (AV)
BUNDLE (BUNDLE OF HIS)
RIGHT AND LEFT
BUNDLE BRANCHES
1
2
3
4
Right atrium
Right ventricle
Frontal plane
SINOATRIAL (SA) NODE
ATRIOVENTRICULAR
(AV) NODE
Left atrium
Left ventricle
Anterior view of frontal section
ATRIOVENTRICULAR (AV)
BUNDLE (BUNDLE OF HIS)
RIGHT AND LEFT
BUNDLE BRANCHES
PURKINJE FIBERS
1
2
3
4
5
Right atrium
Right ventricle

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Electrocardiogram
■ Recording of currents from cardiac
conduction on skin = electrocardiogram
(EKG or ECG)
■ P wave = atrial depolarization
❑ Contraction begins right after peak
❑ Repolarization is masked in QRS
■ QRS complex = Ventricular depolarization
❑ Contraction of ventricle
■ T-wave = ventricular repolarization
❑ Just after ventricles relax

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ECG

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Cardiac Cycle
■ 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%)
■ After QRS ventricular systole
❑ 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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Cardiac Cycle

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Flow Terms
■ Cardiac Output (CO) = liters/min
pumped
■ Heart Rate (HR) = beats/minute (bpm)
■ Stroke volume (SV) = volume/beat
■ CO = HR x SV

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Controls - Stroke Volume (S.V.)
■ Degree of stretch = Frank-Starling law
❑ Increase diastolic Volume increases strength of
contraction increased S.V.
❑ Increased venous return increased S.V.
■ increased sympathetic activity
■ High back pressure in artery decreased
S.V.
❑ Slows semilunar valve opening

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Controls- Heart Rate
■ Pacemaker adjusted by nerves
❑ Cardiovascular center in Medulla
■ parasympathetic- ACh slows
❑ Via vagus nerve
■ Sympathetic - norepinephrine speeds
■ Sensory input for control:
❑ baroreceptors (aortic arch & carotid sinus)-
B.P.
❑ Chemoreceptors- O2
, CO2
, pH

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Other Controls
■ Hormones:
❑ Epinephrine & norepinephrine
increase H.R.
❑ Thyroid hormones stimulate H.R.
❑ Called tachycardia
■ Ions
❑ Increased Na+
or K+
decrease H.R. &
contraction force
❑ Increased Ca2+
increases H.R. &
contraction force

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Autonomic Nervous System Regulation
of Heart Rate

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Exercise and the Heart
■ 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

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End of Chapter 15
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