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The Cardiovascular The Cardiovascular system: Heartsystem: Heart

The Cardiovascular The Cardiovascular system: Heartsystem: Heart

Chapter 15

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LocationLocationLocationLocation

• 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 heartParietal layer fused to fibrous pericardiumInner visceral layer adheres tightly to

heartFilled with pericardial fluid- reduces

friction during beat.

Figure 15.1Figure 15.1

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Heart WallHeart WallHeart WallHeart 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 epitheliumlines inside of myocardium

Figure 15.2aFigure 15.2a

Figure 15.2bFigure 15.2b

Figure 15.2cFigure 15.2c

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ChambersChambersChambersChambers

• 4 chambers• 2 upper chambers= Atria

Between is interatrial septumContains fossa ovalis- remnant of foramen

ovalis

• 2 lower chambers = ventriclesBetween is interventricular septum

• Wall thickness depends on work loadAtria thinnestRight ventricle pumps to lungs & thinner than

left

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Great Vessels Of Heart- Great Vessels Of Heart- RightRight

Great Vessels Of Heart- Great Vessels Of Heart- RightRight

• Superior & inferior Vena CavaeDelivers deoxygenated blood to R. atrium

from bodyCoronary sinus drains heart muscle veins

• R. Atrium R. Ventricle• pumps through Pulmonary TrunkR & L pulmonary arteries• lungs

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Great Vessels Of Heart-Great Vessels Of Heart-LeftLeft

Great Vessels Of Heart-Great Vessels Of Heart-LeftLeft

•Pulmonary Veins from lungsoxygenated blood

L. atrium Left ventricleascending aorta body• Between pulmonary trunk & aortic

arch is ligamentum arteriosum• fetal ductus arteriosum remnant

Figure 15.3aFigure 15.3a

Figure 15.3bFigure 15.3b

Figure 15.3cFigure 15.3c

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ValvesValvesValvesValves

• Designed to prevent back flow in response to pressure changes

• Atrioventricular (AV) valvesBetween 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

Figure 15.4abFigure 15.4ab

Figure 15.4cFigure 15.4c

Figure 15.4dFigure 15.4d

Figure 15.5aFigure 15.5a

Figure 15.5bFigure 15.5b

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Blood Supply Of HeartBlood Supply Of HeartBlood Supply Of HeartBlood Supply Of Heart

• Blood flow through vessels in myocardium = coronary circulation

• L. & Right coronary arteries branch from aortabranch to carry blood throughout

muscle• Deoxygenated blood collected by

Coronary Sinus (posterior)• Empties into R. Atrium

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Conduction SystemConduction SystemConduction SystemConduction System

• 1% of cardiac muscle generate action potentials= Pacemaker & Conduction system

• Normally begins at sinoatrial (SA) node Atria & atria contractAV node -slowsAV bundle (Bundle of His) bundle branches Purkinje fibers apex and up- then ventricles contract

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PacemakerPacemakerPacemakerPacemaker

• 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

Figure 15.6Figure 15.6

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ElectrocardiogramElectrocardiogramElectrocardiogramElectrocardiogram

• Recording of currents from cardiac conduction on skin = electrocardiogram (EKG or ECG)

• P wave= atrial depolarizationContraction begins right after peakRepolarization is masked in QRS

• QRS complex= Ventricular depolarizationContraction of ventricle

• T-wave = ventricular repolarizationJust after ventricles relax

Figure 15.7Figure 15.7

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Cardiac CycleCardiac CycleCardiac CycleCardiac Cycle

• after T-wave ventricular diastoleVentricular pressure drops below atrial & AV

valves open ventricular filling occurs

• After P-wave atrial systoleFinishes filling ventricle (`25%)

• After QRS ventricular systolePressure pushes AV valves closedPushes semilunar valves open and ejection

occursEjection until ventricle relaxes enough for

arterial pressure to close semilunar valves

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Action PotentialAction PotentialAction PotentialAction Potential

• Review muscle• Heart has addition of External

Ca2+

• creates a plateau • prolonged depolarized period.• Can not go into tetanus.

Figure 15.8Figure 15.8

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Flow TermsFlow TermsFlow TermsFlow 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 Controls- Stroke Volume (S.V.)(S.V.)

Controls- Stroke Volume Controls- Stroke Volume (S.V.)(S.V.)

• Degree of stretch = Frank-Starling lawIncrease 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 RateControls- Heart RateControls- Heart RateControls- Heart Rate

• Pacemaker adjusted by nervesCardiovascular center in Medulla

• parasympathetic- ACh slowsVia 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 ControlsOther ControlsOther ControlsOther Controls

• Hormones: Epinephrine & norepinephrine

increase H.R.Thyroid hormones stimulate H.R.Called tachycardia

• IonsIncreased Na+ or K+ decrease H.R. &

contraction forceIncreased Ca2+ increases H.R. &

contraction force

Figure 15.9Figure 15.9

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ExerciseExerciseExerciseExercise

• 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

Figure 15.10Figure 15.10