The Heart

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

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

Gross Anatomy of the Heart (Anterior Aspect)

Gross Anatomy of the Heart (Posterior Surface View)

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

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

Gross Anatomy of the Heart (Frontal Section)

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

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

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

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

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

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

An Electrocardiogram (ECG) Tracing

Summary of Events Occurring in the Heart During the Cardiac Cycle

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

Cardiac Cycle (Part 2) Ventricular filling 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

Cardiac Cycle (Part 3) Ventricular systole Stroke volume = EDV –ESV 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

Factors Involved in Regulation of Cardiac Output

Generalizing Structure of Arteries, Veins, and Capillaries