Cardiovascular System

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Cardiovascular System

• Heart Anatomy
• Coverings
• Muscles
• BVs
• Valves
• Cardiac Physiology
• Electro-chemical events
• Contractility
• Energetics

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Heart Anatomy

• Approximately the size of your fist
• Location
• Superior surface of diaphragm
• Left of the midline
• Anterior to the vertebral column, posterior to
  the sternum

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Coverings of the Heart Anatomy

• Pericardium a double-walled sac around the
  heart composed of
• A superficial fibrous pericardium
• A deep two-layer serous pericardium
• The parietal layer lines the internal surface of
  the fibrous pericardium
• The visceral layer or epicardium lines the
  surface of the heart
• They are separated by the fluid-filled
  pericardial cavity

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Coverings of the Heart Physiological
Significance

• The pericardium
• Protects and anchors the heart
• Prevents overfilling of the heart with blood
• Allows for the heart to work in a relatively
  friction-free environment

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Pericardium Heart Wall
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Heart Wall

• Epicardium visceral layer of the serous
  pericardium
• Myocardium cardiac muscle layer forming the
  bulk of the heart
• Fibrous skeleton of the heart crisscrossing,
  interlacing layer of connective tissue
• Endocardium endothelial layer of the inner
  myocardial surface

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External Heart Major Vessels of the Heart
(Anterior View)

• Vessels returning blood to the heart include
• Superior and inferior venae cavae
• Right and left pulmonary veins
• Vessels conveying blood away from the heart
• Pulmonary trunk, which splits into right and left
  pulmonary arteries
• Ascending aorta (three branches)
  brachiocephalic, left common carotid, and
  subclavian arteries

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External Heart Vessels that Supply/Drain the
Heart (Anterior View)

• Arteries right and left coronary (in
  atrioventricular groove), marginal, circumflex,
  and anterior interventricular arteries
• Veins small cardiac, anterior cardiac, and
  great cardiac veins

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External Heart Major Vessels of the Heart
(Posterior View)

• Vessels returning blood to the heart include
• Right and left pulmonary veins
• Superior and inferior venae cavae
• Vessels conveying blood away from the heart
  include
• Aorta
• Right and left pulmonary arteries

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External Heart Vessels that Supply/Drain the
Heart (Posterior View)

• Arteries right coronary artery (in
  atrioventricular groove) and the posterior
  interventricular artery (in interventricular
  groove)
• Veins great cardiac vein, posterior vein to
  left ventricle, coronary sinus, and middle
  cardiac vein

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Atria of the Heart

• Atria are the receiving chambers of the heart
• Each atrium has a protruding auricle
• Pectinate muscles mark atrial walls
• Blood enters right atria from superior and
  inferior venae cavae and coronary sinus
• Blood enters left atria from pulmonary veins

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Ventricles of the Heart

• Ventricles are the discharging chambers of the
  heart
• Papillary muscles and trabeculae carneae muscles
  mark ventricular walls
• Right ventricle pumps blood into the pulmonary
  trunk
• Left ventricle pumps blood into the aorta

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Pathway of Blood Through the Heart and Lungs

• Right atrium ? tricuspid valve ? right ventricle
• Right ventricle ? pulmonary semilunar valve ?
  pulmonary arteries ? lungs
• Lungs ? pulmonary veins ? left atrium
• Left atrium ? bicuspid valve ? left ventricle
• Left ventricle ? aortic semilunar valve ? aorta
• Aorta ? systemic circulation

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Coronary Circulation

• Coronary circulation is the functional blood
  supply to the heart muscle itself
• Collateral routes ensure blood delivery to heart
  even if major vessels are occluded

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Coronary Circulation Arterial Supply
Figure 18.7a
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Coronary Circulation Venous Supply
Figure 18.7b
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Heart Valves

• Heart valves ensure unidirectional blood flow
  through the heart
• Atrioventricular (AV) valves lie between the
  atria and the ventricles
• AV valves prevent backflow into the atria when
  ventricles contract
• Chordae tendineae anchor AV valves to papillary
  muscles

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Heart Valves

• Aortic semilunar valve lies between the left
  ventricle and the aorta
• Pulmonary semilunar valve lies between the right
  ventricle and pulmonary trunk
• Semilunar valves prevent backflow of blood into
  the ventricles

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4 Heart Valves (2 AV 2SL)
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Atrioventricular Valve Function
Figure 18.9
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Semilunar Valve Function
Figure 18.10
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Microscopic Anatomy of Heart Muscle

• Cardiac muscle is striated, short, fat, branched,
  and interconnected
• The connective tissue endomysium acts as both
  tendon and insertion
• Intercalated discs anchor cardiac cells together
  and allow free passage of ions
• Heart muscle behaves as a functional syncytium

PLAY
InterActive Physiology Anatomy Review The
Heart, pages 37
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Mechanisms of Contraction (skeletal muscle
differences)

• Means of stimulation automaticity or
  autorhythmicity 1 of heart m. cells are
  dedicated to this spontaneous depolarization
• Heart contracts as a unit due to gap junction ion
  transmission in cell to cell propogation
• Absolute refractory period (250ms vs 1-2ms for
  skeletal) inactive period when muscle cant
  contract - prevents tetanic contractions

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Contractile Heart Muscle Fibers (similarity to
skeletal muscle)

• Na influx opens voltage-regulated fast Na
  channels for short incr. in Na permeability
• Depolarization wave passes down T-tubules to
  release Ca from SR into sarcoplasm
• Excitation-contraction coupling occurs as Ca
  binds to the troponin to allow cross-bridges
• Slow Ca channels prolong the contraction phase
  for up to 200ms - plateau

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Heart Physiology

• Energy Requirements
• Incr. mitochondria
• Almost exclusively aerobic
• Fuels
• Glucose, fatty acids, lactic acid, ketone
  bodies
• Setting Rhythm
• Gap Junctions
• Intrinsic Conduction System

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AP of Autorhythmic Cells

• Unstable resting membrane potential continuous
  depolarization towards threshold
• Pacemaker potentials or prepotentials
• Due to gradual reduction in K w/ unchanged Na
  permeability allowing slow influx of Na, results
  in less (more ) membrane potential
• At threshold (-40mV) fast Ca channels open with
  a burst thus Ca controls AP

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Intrinsic System Electrical Sequence

• SA Node superior region of R.Atria
• - 75X/min thus all other centers Pacemaker
• AV Node interatrial septum above Tricuspid
  -0.1s delay allows atrial contraction before
  ventricles due to narrowed fibers.
• AV Bundle (Bundle of His) - crosses the
  disconnect between atria and ventricles)
  superior interventricular septum
• R L Bundle Branches split go to the apex
• Purkinje Fibers complete the pathway to the
  ventricular walls (papillary m. first, then to
  the ventricles)

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Heart Excitation Related to ECG
SA node generates impulse atrial excitation
begins
Impulse delayed at AV node
Impulse passes to heart apex ventricular excitati
on begins
Ventricular excitation complete
SA node
AV node
Purkinje fibers
Bundle branches
Figure 18.17
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Extrinsic Innervation

• Autonomic N.S.
• Sympathetic Cardioacceleratory center in
  medulla go to SA node, AV node, heart muscle,
  and coronary arteries to create excitation and
  increased heart rate
• Parasympathetic Cardioinhibitory center uses
  Cranial n. X (Vagus n.) to SA and AV nodes

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Electrocardiography (ECG or EKG)

• In NOT one AP, rather it is a composite of ALL
  the APs generated by nodal and contractile cells
• 12 leads (3 bipolar and 9 unipolar)
• P wave atrial depolarization lasts 0.08s
  (0.1s to atrial contraction)
• QRS complex ventricular depolarization size
  dependant lasts 0.08s
• T wave ventricular repolarization lasts 0.16s

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Heart Excitation Related to ECG
SA node generates impulse atrial excitation
begins
Impulse delayed at AV node
Impulse passes to heart apex ventricular excitati
on begins
Ventricular excitation complete
SA node
AV node
Purkinje fibers
Bundle branches
Figure 18.17
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Electronic Intervals

• P-Q interval N 0.16s
• P-R interval another descriptor instead of P-Q
• S-T segment AP is in plateau and all the
  ventricular myocardium is depolarized
• Q-T interval N 0.38s time of ventricular
  depolarization through repolarization.

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ECG Interpretations

• Enlarged R may be enlarged ventricles
• Flattened T may mean cardiac ischemia
• Prolonged Q-T interval may be ventricular
  arrhythmias
• Absent or flattened P may be atrial fibrillation
• No QRS with every P is heart block (normally
  11 whole number ratio)
• Chaotic deflections is V-fib seen with heart
  attack or electrical shock

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ECG Tracings

• Normal Sinus Rhythm
• Junctional Rhythm no SA node activity no
  atrial contraction
• 2nd degree heart block
• V-fib

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Mechanical Events of the Cardiac Cycle

• Ventricular Filling mid to late diastole P
  wave and atrial contraction phase create the End
  Diastolic Volume
• Ventricular Systole isovolumetric contraction
  phase followed by ventricular ejection phase
• Isovolumetric relaxation early diastole after T
  wave to create the End Systolic Volume (also see
  the dicrotic notch
• Total time 0.8s (0.1 atria 0.3 ventricles 0.4
  relax)

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Cardiac Output (CO)

• CO HR(75) X SV(70) 5.25L / min
• Preload Degree of Stretch of Heart Muscle fibers
  (Frank-Starling Law) affect EDV
• Contractility enhanced by Ca concentrations )
  plus hormones glucagon, thyroxine, and
  epinephrine and digitalis ( inotropic vs.
  inotropic) that affect ESV
• Afterload Back Pressure Exerted by Arterial
  Blood N80mmHg causes less blood to be ejected if
  80 so ESV is affected

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Developmental Aspects of the Heart

• Fetal heart structures that bypass pulmonary
  circulation
• Foramen ovale connects the two atria
• Ductus arteriosus connects pulmonary trunk and
  the aorta

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Age-Related Changes Affecting the Heart

• Sclerosis and thickening of valve flaps
• Decline in cardiac reserve
• Fibrosis of cardiac muscle
• Atherosclerosis

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Congestive Heart Failure (CHF)

• Congestive heart failure (CHF) is caused by
• Coronary atherosclerosis
• Persistent high blood pressure
• Multiple myocardial infarcts
• Dilated cardiomyopathy (DCM)

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