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The Heart

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Description of the Heart (Part 1)

Heart location Ventral cavity – Thoracic cavity

– Mediastinal cavity – Pericardial cavity

2/3 shifted left Extends from rib 2 to 5th

intercostal space Apex

• Left ventricle• Points toward left hip

Base • Upper posterior surface• Predominantly left atrium

Sternocostal surface Diaphragmatic surface Individual’s heart is about the

size of the person’s closed fist

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Description of the Heart (Part 2)

Pericardial Sac Fibrous pericardium Serous pericardium

• Parietal• Visceral

• Pericardial cavity

Cardiac Wall Epicardium – Visceral

pericardium Myocardium – Muscle

layer Endocardium – Lining

• Chambers• Valves

Clinical Applications CPR Cardiac tamponade Pericarditis Myocarditis Endocarditis

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Gross Anatomy of the Heart (Anterior Aspect)

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Gross Anatomy of the Heart (Posterior Surface View)

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Description of the Heart (Part 3)

Cardiac Chambers Atria

• Thin walls• Pectinate muscle• Separated by

• Interatrial septum• Fossa (foramen)

ovalis• Right

• Receives oxygen depleted blood from body

• Lowest blood pressure in body

• Left• Receives oxygen

enriched blood from lungs

Ventricles• Thick walls• Trabeculae carnae• Separated by –

Interventricular septum

• Right• Receives blood

from R. Atrium

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Description of the Heart (Part 4)

• Pumps blood to lungs• Left

• Receives blood from L. atrium

• Pumps blood to body• Highest blood

pressure

Cardiac Valves Structure

• Cusp• Endocardium• Dense connective

tissue• Chordae tendinae• Papillary muscle

Function• Prevent reverse flow

Location & surface projection

• Tricuspid• R. atrioventricular

valve• R./L. 5th intercostal

space, near sternum• Pulmonary semilunar

• R. ventricle pulmonary trunk

• L., 2nd intercostal space near sternum

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Gross Anatomy of the Heart (Frontal Section)

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Description of the Heart (Part 5)

• Bicuspid (mitral)• L. atrioventricular • L., 5th intercostal space in midclavicular line

• Aortic semilunar• L. ventricle aorta• R., 2nd intercostal space, near sternum

Great vessels of the Heart

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Description of the Heart (Part 6)

Inferior vena cava (IVC) Coronary sinus Superior vena cava (SVC) Pulmonary trunk – Right ventricle Pulmonary veins – Left atrium Aorta – Left ventricle

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Cardiac Conduction System (Part 1)

Specialized myocardial cells Autorhythmic Pacemaker Conduction system

Pacemaker cells set up basic rhythm of contractions

Conduction system coordinates contraction of myocardial fibers

Conduction system components Sinoatrial (SA) node

• In R. atrium near SVC opening

• Primary pacemaker• Impulse transmits to AV

node• Maintains rhythm of 60-

100 bpm Atrioentricular (AV) node

• In interatrial septum• Secondary pacemaker• Impulse transmits to AV

bundle

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The Intrinsic Conduction of the Heart and Succession of Action Potential Through Selected Areas

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Cardiac Conduction System (Part 2)

• Sets basic rhythm if SA node is not functioning

• Maintains rhythm of 40-50

Atrioventricular bundle (Bundle of His)

• Electrically links atria to ventricles

• In septa• Impulse transmits to

bundle branches• Maintains rhythm of

20-40

R.&L. bundle branches In interventricular septum Impulses transmit to

myoconduction fibers Conduction myofibers

(Pukinje fibers)• In ventricular walls• Impulses transmit to

ventricular walls Clinical applications

Artificial pacemakers Bundle branch block

• Complete• Right • Left

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The Sequence of Excitation of the Heart Related to the Deflection Waves of an ECG Tracing

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An Electrocardiogram (ECG) Tracing

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Summary of Events Occurring in the Heart During the Cardiac Cycle

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Cardiac Cycle (Part 1)

Events associated with one heart beat – Lasts about 0.8 sec

R. & L. sides Acts simultaneously Develop different

pressures Expel the same volume

Chambers fill passively Atria contract while

ventricles relax Ventricles contract while

atria relax

Systole – Contraction phase

Asystole – Relaxation phase

Phases Relaxation (Quiescent)

period• At end of heart beat –

lasts about 0.4 sec• All 4 chambers relaxed –

Pressure drops backflow of blood

• Trapped by closing of semilunar cusps of vavles – Dicrotic notch

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Cardiac Cycle (Part 2)

• All 4 valves closed – Isovolumetric relaxation• Ventricular pressure < atrial pressure – AV

valves open Ventricular filling

• Rapid ventricular filling – Passive • Diastasis• Atrial systole – Final 30mL – 0.1 sec• End diastolic volume (EDV) – about 130 mL

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Cardiac Cycle (Part 3)

Ventricular systole• AV valves shut – 1st heart sound• All 4 valves closed – Isovolumetric contraction• Ventricular pressure rises• Semilunar valves open• Ventricular ejection – 0.5 sec• Semilunar valves close – 2nd heart sound• Systole begins• End systolic volume (ESV) – 60 mL

Stroke volume = EDV –ESV Cardiac output = stroke volume x heart rate

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Factors Involved in Regulation of Cardiac Output

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Generalizing Structure of Arteries, Veins, and Capillaries