The Cardiovascular system: Heart

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The Cardiovascular system Heart

• Chapter 15

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Location

• 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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Figure 15.1
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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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Figure 15.2a
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Figure 15.2b
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Figure 15.2c
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Chambers

• 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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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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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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Figure 15.3a
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Figure 15.3b
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Figure 15.3c
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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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Figure 15.4ab
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Figure 15.4c
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Figure 15.4d
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Figure 15.5a
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Figure 15.5b
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Blood Supply Of Heart

• Blood flow through vessels in myocardium
  coronary circulation
• L. Right coronary arteries
• branch from aorta
• branch to carry blood throughout muscle
• Deoxygenated blood collected by Coronary Sinus
  (posterior)
• Empties into R. 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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Figure 15.6
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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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Figure 15.7
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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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Action Potential

• Review muscle
• Heart has addition of External Ca2
• creates a plateau
• prolonged depolarized period.
• Can not go into tetanus.

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Figure 15.8
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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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Figure 15.9
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Exercise

• 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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Figure 15.10