18 The Cardiovascular System: The Heart: Part A.

18 The Cardiovascular System: The Heart: Part A

The Pulmonary and Systemic Circuits
Heart is transport system; two side-by-side pumps Right side receives oxygen-poor blood from tissues Pumps to lungs to get rid of CO2, pick up O2, via pulmonary circuit Left side receives oxygenated blood from lungs Pumps to body tissues via systemic circuit © 2013 Pearson Education, Inc.

Figure 18.1 The systemic and pulmonary circuits.
Capillary beds of lungs where gas exchange occurs Pulmonary Circuit Pulmonary arteries Pulmonary veins Aorta and branches Venae cavae Left atrium Left ventricle Right atrium Heart Right ventricle Systemic Circuit Capillary beds of all body tissues where gas exchange occurs Oxygen-rich, CO2-poor blood Oxygen-poor, CO2-rich blood © 2013 Pearson Education, Inc.

Approximately size of fist Location:
Heart Anatomy Approximately size of fist Location: In mediastinum between second rib and fifth intercostal space On superior surface of diaphragm Two-thirds of heart to left of midsternal line Anterior to vertebral column, posterior to sternum PLAY Animation: Rotatable heart © 2013 Pearson Education, Inc.

Base (posterior surface) leans toward right shoulder
Heart Anatomy Base (posterior surface) leans toward right shoulder Apex points toward left hip Apical impulse palpated between fifth and sixth ribs, just below left nipple © 2013 Pearson Education, Inc.

Figure 18.2a Location of the heart in the mediastinum.
Midsternal line 2nd rib Sternum Diaphragm Location of apical impulse © 2013 Pearson Education, Inc.

Figure 18.2b Location of the heart in the mediastinum.
Left lung Body of T7 vertebra Posterior © 2013 Pearson Education, Inc. 9

Figure 18.2c Location of the heart in the mediastinum.
Superior vena cava Aorta Parietal pleura (cut) Pulmonary trunk Left lung Pericardium (cut) Apex of heart Diaphragm © 2013 Pearson Education, Inc.

Coverings of the Heart: Pericardium
Double-walled sac Superficial fibrous pericardium Protects, anchors to surrounding structures, and prevents overfilling © 2013 Pearson Education, Inc.

Deep two-layered serous pericardium
Parietal layer lines internal surface of fibrous pericardium Visceral layer (epicardium) on external surface of heart Two layers separated by fluid-filled pericardial cavity (decreases friction) © 2013 Pearson Education, Inc.

Homeostatic Imbalance
Pericarditis Inflammation of pericardium Roughens membrane surfaces  pericardial friction rub (creaking sound) heard with stethoscope Cardiac tamponade Excess fluid sometimes compresses heart  limited pumping ability © 2013 Pearson Education, Inc.

Layers of the Heart Wall
Three layers of heart wall: Epicardium Myocardium Endocardium Visceral layer of serous pericardium © 2013 Pearson Education, Inc.

Myocardium Spiral bundles of contractile cardiac muscle cells Cardiac skeleton: crisscrossing, interlacing layer of connective tissue Anchors cardiac muscle fibers Supports great vessels and valves Limits spread of action potentials to specific paths © 2013 Pearson Education, Inc.

Figure 18.3 The pericardial layers and layers of the heart wall.
Pulmonary trunk Fibrous pericardium Parietal layer of serous pericardium Pericardium Myocardium Pericardial cavity Epicardium (visceral layer of serous pericardium) Heart wall Myocardium Endocardium Heart chamber © 2013 Pearson Education, Inc.

Cardiac muscle bundles
Figure The circular and spiral arrangement of cardiac muscle bundles in the myocardium of the heart. Cardiac muscle bundles © 2013 Pearson Education, Inc.

Interatrial septum – separates atria
Chambers Four chambers: Two superior atria Two inferior ventricles Interatrial septum – separates atria Fossa ovalis – remnant of foramen ovale of fetal heart Interventricular septum – separates ventricles © 2013 Pearson Education, Inc.

Figure 18.5e Gross anatomy of the heart.
Aorta Left pulmonary artery Superior vena cava Left atrium Right pulmonary artery Left pulmonary veins Pulmonary trunk Right atrium Mitral (bicuspid) valve Right pulmonary veins Fossa ovalis Aortic valve Pectinate muscles Pulmonary valve Tricuspid valve Left ventricle Right ventricle Papillary muscle Chordae tendineae Interventricular septum Trabeculae carneae Epicardium Inferior vena cava Myocardium Endocardium Frontal section © 2013 Pearson Education, Inc.

Chambers and Associated Great Vessels
Coronary sulcus (atrioventricular groove) Encircles junction of atria and ventricles Anterior interventricular sulcus Anterior position of interventricular septum Posterior interventricular sulcus Landmark on posteroinferior surface © 2013 Pearson Education, Inc.

Atria: The Receiving Chambers
Auricles Appendages that increase atrial volume Right atrium Pectinate muscles Posterior and anterior regions separated by crista terminalis Left atrium Pectinate muscles only in auricles © 2013 Pearson Education, Inc.

Atria: The Receiving Chambers
Small, thin-walled Contribute little to propulsion of blood Three veins empty into right atrium: Superior vena cava, inferior vena cava, coronary sinus Four pulmonary veins empty into left atrium © 2013 Pearson Education, Inc.

Ventricles: The Discharging Chambers
Most of the volume of heart Right ventricle - most of anterior surface Left ventricle – posteroinferior surface Trabeculae carneae – irregular ridges of muscle on walls Papillary muscles – anchor chordae tendineae © 2013 Pearson Education, Inc.

Ventricles: The Discharging Chambers
Thicker walls than atria Actual pumps of heart Right ventricle Pumps blood into pulmonary trunk Left ventricle Pumps blood into aorta (largest artery in body) © 2013 Pearson Education, Inc.

Figure 18.5b Gross anatomy of the heart.
Left common carotid artery Brachiocephalic trunk Left subclavian artery Superior vena cava Aortic arch Ligamentum arteriosum Right pulmonary artery Left pulmonary artery Ascending aorta Left pulmonary veins Pulmonary trunk Auricle of left atrium Right pulmonary veins Circumflex artery Right atrium Right coronary artery (in coronary sulcus) Left coronary artery (in coronary sulcus) Anterior cardiac vein Left ventricle Right ventricle Right marginal artery Great cardiac vein Anterior interventricular artery (in anterior interventricular sulcus) Small cardiac vein Inferior vena cava Apex Anterior view © 2013 Pearson Education, Inc.

Figure 18.5a Gross anatomy of the heart.
Aortic arch (fat covered) Pulmonary trunk Auricle of right atrium Auricle of left atrium Anterior interventricular artery Right ventricle Apex of heart (left ventricle) Anterior aspect (pericardium removed) © 2013 Pearson Education, Inc.

Figure 18.5f Gross anatomy of the heart.
Ascending aorta (cut open) Superior vena cava Pulmonary trunk Aortic valve Right ventricle anterior wall (retracted) Pulmonary valve Trabeculae carneae Interventricular septum (cut) Opening to right atrium Left ventricle Papillary muscles Chordae tendineae Right ventricle Photograph; view similar to (e) © 2013 Pearson Education, Inc.

Heart Valves Ensure unidirectional blood flow through heart
Open and close in response to pressure changes Two atrioventricular (AV) valves Prevent backflow into atria when ventricles contract Tricuspid valve (right AV valve) Mitral valve (left AV valve, bicuspid valve) Chordae tendineae anchor cusps to papillary muscles Hold valve flaps in closed position © 2013 Pearson Education, Inc.

Figure 18.7 The atrioventricular (AV) valves.
Blood returning to the heart fills atria, pressing against the AV valves. The increased pressure forces AV valves open. 1 Direction of blood flow Atrium Cusp of atrioventricular valve (open) As ventricles fill, AV valve flaps hang limply into ventricles. 2 Chordae tendineae Atria contract, forcing additional blood into ventricles. 3 Papillary muscle Ventricle AV valves open; atrial pressure greater than ventricular pressure Atrium Cusps of atrioventricular valve (closed) Ventricles contract, forcing blood against AV valve cusps. 1 2 AV valves close. Blood in ventricle Papillary muscles contract and chordae tendineae tighten, preventing valve flaps from everting into atria. 3 AV valves closed; atrial pressure less than ventricular pressure © 2013 Pearson Education, Inc.

Two semilunar (SL) valves
Heart Valves Two semilunar (SL) valves Prevent backflow into ventricles when ventricles relax Open and close in response to pressure changes Aortic semilunar valve Pulmonary semilunar valve © 2013 Pearson Education, Inc.

Figure 18.8 The semilunar (SL) valves.
Aorta Pulmonary trunk As ventricles contract and intraventricular pressure rises, blood is pushed up against semilunar valves, forcing them open. Semilunar valves open As ventricles relax and intraventricular pressure falls, blood flows back from arteries, filling the cusps of semilunar valves and forcing them to close. Semilunar valves closed © 2013 Pearson Education, Inc.

(left atrioventricular) valve
Figure 18.6a Heart valves. Pulmonary valve Aortic valve Area of cutaway Mitral valve Tricuspid valve Myocardium Mitral (left atrioventricular) valve Tricuspid (right atrioventricular) valve Aortic valve Pulmonary valve Cardiac skeleton Anterior © 2013 Pearson Education, Inc.

(left atrioventricular) valve
Figure 18.6b Heart valves. Pulmonary valve Aortic valve Area of cutaway Mitral valve Tricuspid valve Myocardium Mitral (left atrioventricular) valve Tricuspid (right atrioventricular) valve Aortic valve Pulmonary valve © 2013 Pearson Education, Inc.

Chordae tendineae attached to tricuspid valve flap Papillary muscle
Figure 18.6c Heart valves. Pulmonary valve Aortic valve Area of cutaway Mitral valve Tricuspid valve Chordae tendineae attached to tricuspid valve flap Papillary muscle © 2013 Pearson Education, Inc.

Pulmonary valve Aortic valve Area of cutaway Mitral valve
Figure 18.6d Heart valves. Pulmonary valve Aortic valve Area of cutaway Mitral valve Tricuspid valve Opening of inferior vena cava Mitral valve Chordae tendineae Tricuspid valve Myocardium of right ventricle Interventricular septum Papillary muscles Myocardium of left ventricle © 2013 Pearson Education, Inc.

Two conditions severely weaken heart: Incompetent valve Blood backflows so heart repumps same blood over and over Valvular stenosis Stiff flaps – constrict opening  heart must exert more force to pump blood Valve replaced with mechanical, animal, or cadaver valve © 2013 Pearson Education, Inc.

Pathway of Blood Through the Heart
Pulmonary circuit Right atrium  tricuspid valve  right ventricle Right ventricle  pulmonary semilunar valve  pulmonary trunk  pulmonary arteries  lungs Lungs  pulmonary veins  left atrium © 2013 Pearson Education, Inc.

Systemic circuit Left atrium  mitral valve  left ventricle Left ventricle  aortic semilunar valve  aorta Aorta  systemic circulation PLAY Animation: Rotatable heart (sectioned) © 2013 Pearson Education, Inc.

Superior vena cava (SVC) Inferior vena cava (IVC)
Figure The heart is a double pump, each side supplying its own circuit. Slide 1 Both sides of the heart pump at the same time, but let’s follow one spurt of blood all the way through the system. Oxygen-poor blood Oxygen-rich blood Pulmonary Semilunar valve Tricuspid valve Superior vena cava (SVC) Inferior vena cava (IVC) Coronary sinus Right atrium Right ventricle Pulmonary trunk Pulmonary arteries SVC Tricuspid valve Coronary sinus Pulmonary trunk Right atrium Pulmonary semilunar valve Right ventricle IVC Oxygen-poor blood is carried in two pulmonary arteries to the lungs (pulmonary circuit) to be oxygenated. Oxygen-poor blood returns from the body tissues back to the heart. To heart To lungs Systemic capillaries Pulmonary capillaries Oxygen-rich blood is delivered to the body tissues (systemic circuit). Oxygen-rich blood returns to the heart via the four pulmonary veins. To body To heart Aorta Pulmonary veins Aortic semilunar valve Mitral valve Left atrium Left ventricle Aortic Semilunar valve Mitral valve Four pulmonary veins Left ventricle Left atrium Aorta © 2013 Pearson Education, Inc.

Figure The heart is a double pump, each side supplying its own circuit. Slide 2 Superior vena cava (SVC) Inferior vena cava (IVC) Coronary sinus Oxygen-poor blood Oxygen-rich blood SVC Coronary sinus IVC © 2013 Pearson Education, Inc. 41

Figure The heart is a double pump, each side supplying its own circuit. Slide 3 Superior vena cava (SVC) Inferior vena cava (IVC) Coronary sinus Oxygen-poor blood Right atrium Oxygen-rich blood SVC Coronary sinus Right atrium IVC © 2013 Pearson Education, Inc. 42

Figure The heart is a double pump, each side supplying its own circuit. Slide 4 Tricuspid valve Superior vena cava (SVC) Inferior vena cava (IVC) Coronary sinus Right atrium Right ventricle Oxygen-poor blood Oxygen-rich blood SVC Tricuspid valve Coronary sinus Right atrium Right ventricle IVC © 2013 Pearson Education, Inc. 43

Figure The heart is a double pump, each side supplying its own circuit. Slide 5 Pulmonary Semilunar valve Tricuspid valve Superior vena cava (SVC) Inferior vena cava (IVC) Coronary sinus Right atrium Right ventricle Pulmonary trunk Oxygen-poor blood Oxygen-rich blood Pulmonary arteries SVC Coronary sinus Tricuspid valve Pulmonary trunk Right atrium Pulmonary semilunar valve Right ventricle IVC © 2013 Pearson Education, Inc. 44

Figure The heart is a double pump, each side supplying its own circuit. Slide 6 Oxygen-poor blood Pulmonary Semilunar valve Oxygen-rich blood Tricuspid valve Superior vena cava (SVC) Inferior vena cava (IVC) Coronary sinus Right atrium Right ventricle Pulmonary trunk Pulmonary arteries SVC Coronary sinus Tricuspid valve Pulmonary trunk Right atrium Pulmonary semilunar valve Right ventricle IVC Oxygen-poor blood is carried in two pulmonary arteries to the lungs (pulmonary circuit) to be oxygenated. To lungs Pulmonary capillaries © 2013 Pearson Education, Inc. 45

Pulmonary veins Four pulmonary veins Oxygen-poor blood
Figure The heart is a double pump, each side supplying its own circuit. Slide 7 Oxygen-poor blood Pulmonary veins Oxygen-rich blood Four pulmonary veins © 2013 Pearson Education, Inc. 46

Blood Flow Through the Heart
Figure The heart is a double pump, each side supplying its own circuit. Oxygen-poor blood Slide 8 Blood Flow Through the Heart Oxygen-rich blood Pulmonary veins Right ventricle Left atrium Four pulmonary veins Left atrium © 2013 Pearson Education, Inc. 47

Oxygen-rich blood Mitral valve
Figure The heart is a double pump, each side supplying its own circuit. Slide 9 Oxygen-poor blood Oxygen-rich blood Pulmonary veins Left atrium Mitral valve Left ventricle Mitral valve Four pulmonary veins Left ventricle Left atrium © 2013 Pearson Education, Inc. 48

Oxygen-rich blood Aortic Semilunar valve Mitral valve
Figure The heart is a double pump, each side supplying its own circuit. Slide 10 Oxygen-poor blood Oxygen-rich blood Right ventricle Aorta Pulmonary veins Aortic semilunar valve Left atrium Mitral valve Left ventricle Aortic Semilunar valve Mitral valve Four pulmonary veins Left ventricle Left atrium Aorta © 2013 Pearson Education, Inc. 49

Blood Flow Through the Heart
Figure The heart is a double pump, each side supplying its own circuit. Slide 11 Blood Flow Through the Heart Oxygen-poor blood Oxygen-rich blood Systemic capillaries Oxygen-rich blood is delivered to the body tissues (systemic circuit). To body Aorta Pulmonary veins Aortic semilunar valve Left atrium Mitral valve Left ventricle Aortic Semilunar valve Mitral valve Four pulmonary veins Left ventricle Left atrium Aorta © 2013 Pearson Education, Inc. 50

Figure The heart is a double pump, each side supplying its own circuit. Slide 12 Both sides of the heart pump at the same time, but let’s follow one spurt of blood all the way through the system. Oxygen-poor blood Oxygen-rich blood Pulmonary Semilunar valve Tricuspid valve Superior vena cava (SVC) Inferior vena cava (IVC) Coronary sinus Right atrium Right ventricle Pulmonary trunk Pulmonary arteries SVC Tricuspid valve Coronary sinus Pulmonary trunk Right atrium Pulmonary semilunar valve Right ventricle IVC Oxygen-poor blood is carried in two pulmonary arteries to the lungs (pulmonary circuit) to be oxygenated. Oxygen-poor blood returns from the body tissues back to the heart. To heart To lungs Systemic capillaries Pulmonary capillaries Oxygen-rich blood is delivered to the body tissues (systemic circuit). Oxygen-rich blood returns to the heart via the four pulmonary veins. To body To heart Aorta Pulmonary veins Aortic semilunar valve Mitral valve Left atrium Left ventricle Aortic Semilunar valve Mitral valve Four pulmonary veins Left ventricle Left atrium Aorta © 2013 Pearson Education, Inc. 51

Equal volumes of blood pumped to pulmonary and systemic circuits Pulmonary circuit short, low-pressure circulation Systemic circuit long, high-friction circulation Anatomy of ventricles reflects differences Left ventricle walls 3X thicker than right Pumps with greater pressure © 2013 Pearson Education, Inc.

Left Right ventricle Interventricular septum
Figure Anatomical differences between the right and left ventricles. Right ventricle Interventricular septum Left © 2013 Pearson Education, Inc.

Functional blood supply to heart muscle itself
Coronary Circulation Functional blood supply to heart muscle itself Delivered when heart relaxed Left ventricle receives most blood supply Arterial supply varies among individuals Contains many anastomoses (junctions) Provide additional routes for blood delivery Cannot compensate for coronary artery occlusion © 2013 Pearson Education, Inc.

Coronary Circulation: Arteries
Arteries arise from base of aorta Left coronary artery branches  anterior interventricular artery and circumflex artery Supplies interventricular septum, anterior ventricular walls, left atrium, and posterior wall of left ventricle Right coronary artery branches  right marginal artery and posterior interventricular artery Supplies right atrium and most of right ventricle © 2013 Pearson Education, Inc.

Figure 18.11a Coronary circulation.
Aorta Superior vena cava Anastomosis (junction of vessels) Right atrium coronary artery ventricle marginal Posterior interventricular Anterior Left Circumflex Left atrium Pulmonary trunk The major coronary arteries © 2013 Pearson Education, Inc.

Coronary Circulation: Veins
Cardiac veins collect blood from capillary beds Coronary sinus empties into right atrium; formed by merging cardiac veins Great cardiac vein of anterior interventricular sulcus Middle cardiac vein in posterior interventricular sulcus Small cardiac vein from inferior margin Several anterior cardiac veins empty directly into right atrium anteriorly © 2013 Pearson Education, Inc.

Figure 18.11b Coronary circulation.
Superior vena cava Anterior cardiac veins Small cardiac vein Middle cardiac vein Coronary sinus Great vein The major cardiac veins © 2013 Pearson Education, Inc.

Figure 18.5d Gross anatomy of the heart.
Aorta Superior vena cava Right pulmonary artery Left pulmonary artery Right pulmonary veins Left pulmonary veins Auricle of left atrium Right atrium Left atrium Inferior vena cava Great cardiac vein Coronary sinus Right coronary artery (in coronary sulcus) Posterior vein of left ventricle Posterior interventricular artery (in posterior interventricular sulcus) Left ventricle Middle cardiac vein Right ventricle Apex Posterior surface view © 2013 Pearson Education, Inc.

Homeostatic Imbalances
Angina pectoris Thoracic pain caused by fleeting deficiency in blood delivery to myocardium Cells weakened Myocardial infarction (heart attack) Prolonged coronary blockage Areas of cell death repaired with noncontractile scar tissue © 2013 Pearson Education, Inc.

Microscopic Anatomy of Cardiac Muscle
Cardiac muscle cells striated, short, branched, fat, interconnected, 1 (perhaps 2) central nuclei Connective tissue matrix (endomysium) connects to cardiac skeleton Contains numerous capillaries T tubules wide, less numerous; SR simpler than in skeletal muscle Numerous large mitochondria (25–35% of cell volume) © 2013 Pearson Education, Inc.

Figure 18.12a Microscopic anatomy of cardiac muscle.
Intercalated discs Cardiac muscle cell Nucleus Gap junctions Desmosomes © 2013 Pearson Education, Inc.

Microscopic Anatomy of Cardiac Muscle
Intercalated discs - junctions between cells - anchor cardiac cells Desmosomes prevent cells from separating during contraction Gap junctions allow ions to pass from cell to cell; electrically couple adjacent cells Allows heart to be functional syncytium Behaves as single coordinated unit © 2013 Pearson Education, Inc.

Figure 18.12b Microscopic anatomy of cardiac muscle.
cell Mitochondrion Nucleus Intercalated disc Mitochondrion T tubule Sarcoplasmic reticulum Z disc Nucleus Sarcolemma I band A band I band © 2013 Pearson Education, Inc.

Cardiac Muscle Contraction
Three differences from skeletal muscle: ~1% of cells have automaticity (autorhythmicity) Do not need nervous system stimulation Can depolarize entire heart All cardiomyocytes contract as unit, or none do Long absolute refractory period (250 ms) Prevents tetanic contractions © 2013 Pearson Education, Inc.

Three similarities with skeletal muscle: Depolarization opens few voltage-gated fast Na+ channels in sarcolemma  Reversal of membrane potential from –90 mV to +30 mV Brief; Na channels close rapidly Depolarization wave down T tubules  SR to release Ca2+  Excitation-contraction coupling occurs Ca2+ binds troponin  filaments slide © 2013 Pearson Education, Inc.

Figure 18.13 The action potential of contractile cardiac muscle cells.
Slide 1 Action potential Depolarization is due to Na+ influx through fast voltage-gated Na+ channels. A positive feedback cycle rapidly opens many Na+ channels, reversing the membrane potential. Channel inactivation ends this phase. 1 2 3 20 Plateau 2 Tension development (contraction) –20 Membrane potential (mV) Tension (g) Plateau phase is due to Ca2+ influx through slow Ca2+ channels. This keeps the cell depolarized because few K+ channels are open. 1 3 –40 –60 Absolute refractory period –80 Repolarization is due to Ca2+ channels inactivating and K+ channels opening. This allows K+ efflux, which brings the membrane potential back to its resting voltage. 150 300 Time (ms) © 2013 Pearson Education, Inc.

Slide 2 Action potential Depolarization is due to Na+ influx through fast voltage-gated Na+ channels. A positive feedback cycle rapidly opens many Na+ channels, reversing the membrane potential. Channel inactivation ends this phase. 1 20 Plateau Tension development (contraction) –20 Membrane potential (mV) Tension (g) 1 –40 –60 Absolute refractory period –80 150 300 Time (ms) © 2013 Pearson Education, Inc. 69

Slide 3 Action potential Depolarization is due to Na+ influx through fast voltage-gated Na+ channels. A positive feedback cycle rapidly opens many Na+ channels, reversing the membrane potential. Channel inactivation ends this phase. 1 20 Plateau 2 Tension development (contraction) –20 Membrane potential (mV) Tension (g) Plateau phase is due to Ca2+ influx through slow Ca2+ channels. This keeps the cell depolarized because few K+ channels are open. 2 1 –40 –60 Absolute refractory period –80 150 300 Time (ms) © 2013 Pearson Education, Inc. 70

Slide 4 Action potential Depolarization is due to Na+ influx through fast voltage-gated Na+ channels. A positive feedback cycle rapidly opens many Na+ channels, reversing the membrane potential. Channel inactivation ends this phase. 1 2 3 20 Plateau 2 Tension development (contraction) –20 Membrane potential (mV) Tension (g) Plateau phase is due to Ca2+ influx through slow Ca2+ channels. This keeps the cell depolarized because few K+ channels are open. 1 3 –40 –60 Absolute refractory period –80 Repolarization is due to Ca2+ channels inactivating and K+ channels opening. This allows K+ efflux, which brings the membrane potential back to its resting voltage. 150 300 Time (ms) © 2013 Pearson Education, Inc. 71

Energy Requirements Cardiac muscle Has many mitochondria
Great dependence on aerobic respiration Little anaerobic respiration ability Readily switches fuel source for respiration Even uses lactic acid from skeletal muscles © 2013 Pearson Education, Inc.

Ischemic cells  anaerobic respiration  lactic acid  High H+ concentration  high Ca2+ concentration  Mitochondrial damage  decreased ATP production  Gap junctions close  fatal arrhythmias © 2013 Pearson Education, Inc.

Heart Physiology: Electrical Events
Heart depolarizes and contracts without nervous system stimulation Rhythm can be altered by autonomic nervous system © 2013 Pearson Education, Inc.

Heart Physiology: Setting the Basic Rhythm
Coordinated heartbeat is a function of Presence of gap junctions Intrinsic cardiac conduction system Network of noncontractile (autorhythmic) cells Initiate and distribute impulses  coordinated depolarization and contraction of heart © 2013 Pearson Education, Inc.

Sequence of Excitation
Cardiac pacemaker cells pass impulses, in order, across heart in ~220 ms Sinoatrial node  Atrioventricular node  Atrioventricular bundle  Right and left bundle branches  Subendocardial conducting network (Purkinje fibers) © 2013 Pearson Education, Inc.

Heart Physiology: Sequence of Excitation
Sinoatrial (SA) node Pacemaker of heart in right atrial wall Depolarizes faster than rest of myocardium Generates impulses about 75X/minute (sinus rhythm) Inherent rate of 100X/minute tempered by extrinsic factors Impulse spreads across atria, and to AV node © 2013 Pearson Education, Inc.

Atrioventricular (AV) node In inferior interatrial septum Delays impulses approximately 0.1 second Because fibers are smaller diameter, have fewer gap junctions Allows atrial contraction prior to ventricular contraction Inherent rate of 50X/minute in absence of SA node input © 2013 Pearson Education, Inc.

Atrioventricular (AV) bundle (bundle of His) In superior interventricular septum Only electrical connection between atria and ventricles Atria and ventricles not connected via gap junctions © 2013 Pearson Education, Inc.

Subendocardial conducting network Complete pathway through interventricular septum into apex and ventricular walls More elaborate on left side of heart AV bundle and subendocardial conducting network depolarize 30X/minute in absence of AV node input Ventricular contraction immediately follows from apex toward atria © 2013 Pearson Education, Inc.

Superior vena cava Right atrium Internodal pathway Left atrium
Figure 18.15a Intrinsic cardiac conduction system and action potential succession during one heartbeat. Slide 1 Superior vena cava Right atrium The sinoatrial (SA) node (pacemaker) generates impulses. 1 Internodal pathway The impulses pause (0.1 s) at the atrioventricular (AV) node. 2 Left atrium The atrioventricular (AV) bundle connects the atria to the ventricles. 3 Subendocardial conducting network (Purkinje fibers) The bundle branches conduct the impulses through the interventricular septum. 4 Inter- ventricular septum The subendocardial conducting network depolarizes the contractile cells of both ventricles. 5 Anatomy of the intrinsic conduction system showing the sequence of electrical excitation © 2013 Pearson Education, Inc.

Figure 18.15a Intrinsic cardiac conduction system and action potential succession during one heartbeat. Slide 2 Superior vena cava Right atrium The sinoatrial (SA) node (pacemaker) generates impulses. 1 Internodal pathway Left atrium Subendocardial conducting network (Purkinje fibers) Inter- ventricular septum Anatomy of the intrinsic conduction system showing the sequence of electrical excitation © 2013 Pearson Education, Inc. 83

Figure 18.15a Intrinsic cardiac conduction system and action potential succession during one heartbeat. Slide 3 Superior vena cava Right atrium The sinoatrial (SA) node (pacemaker) generates impulses. 1 Internodal pathway The impulses pause (0.1 s) at the atrioventricular (AV) node. 2 Left atrium Subendocardial conducting network (Purkinje fibers) Inter- ventricular septum Anatomy of the intrinsic conduction system showing the sequence of electrical excitation © 2013 Pearson Education, Inc. 84

Figure 18.15a Intrinsic cardiac conduction system and action potential succession during one heartbeat. Slide 4 Superior vena cava Right atrium The sinoatrial (SA) node (pacemaker) generates impulses. 1 Internodal pathway The impulses pause (0.1 s) at the atrioventricular (AV) node. 2 Left atrium The atrioventricular (AV) bundle connects the atria to the ventricles. 3 Subendocardial conducting network (Purkinje fibers) Inter- ventricular septum Anatomy of the intrinsic conduction system showing the sequence of electrical excitation © 2013 Pearson Education, Inc. 85

Figure 18.15a Intrinsic cardiac conduction system and action potential succession during one heartbeat. Slide 5 Superior vena cava Right atrium The sinoatrial (SA) node (pacemaker) generates impulses. 1 Internodal pathway The impulses pause (0.1 s) at the atrioventricular (AV) node. 2 Left atrium The atrioventricular (AV) bundle connects the atria to the ventricles. 3 Subendocardial conducting network (Purkinje fibers) The bundle branches conduct the impulses through the interventricular septum. 4 Inter- ventricular septum Anatomy of the intrinsic conduction system showing the sequence of electrical excitation © 2013 Pearson Education, Inc. 86

Figure 18.15a Intrinsic cardiac conduction system and action potential succession during one heartbeat. Slide 6 Superior vena cava Right atrium The sinoatrial (SA) node (pacemaker) generates impulses. 1 Internodal pathway The impulses pause (0.1 s) at the atrioventricular (AV) node. 2 Left atrium The atrioventricular (AV) bundle connects the atria to the ventricles. 3 Subendocardial conducting network (Purkinje fibers) The bundle branches conduct the impulses through the interventricular septum. 4 Inter- ventricular septum The subendocardial conducting network depolarizes the contractile cells of both ventricles. 5 Anatomy of the intrinsic conduction system showing the sequence of electrical excitation © 2013 Pearson Education, Inc. 87

Pacemaker potential Plateau 100 200 300 400
Figure 18.15b Intrinsic cardiac conduction system and action potential succession during one heartbeat. Pacemaker potential SA node Atrial muscle AV node Pacemaker potential Ventricular muscle Plateau 100 200 300 400 Milliseconds Comparison of action potential shape at various locations © 2013 Pearson Education, Inc.

Defects in intrinsic conduction system may cause Arrhythmias - irregular heart rhythms Uncoordinated atrial and ventricular contractions Fibrillation - rapid, irregular contractions; useless for pumping blood  circulation ceases  brain death Defibrillation to treat © 2013 Pearson Education, Inc.

Defective SA node may cause Ectopic focus - abnormal pacemaker AV node may take over; sets junctional rhythm (40–60 beats/min) Extrasystole (premature contraction) Ectopic focus sets high rate Can be from excessive caffeine or nicotine © 2013 Pearson Education, Inc.

To reach ventricles, impulse must pass through AV node Defective AV node may cause Heart block Few (partial) or no (total) impulses reach ventricles Ventricles beat at intrinsic rate – too slow for life Artificial pacemaker to treat © 2013 Pearson Education, Inc.

Extrinsic Innervation of the Heart
Heartbeat modified by ANS via cardiac centers in medulla oblongata Sympathetic   rate and force Parasympathetic   rate © 2013 Pearson Education, Inc.

Electrocardiogram (ECG or EKG)
Electrocardiography Electrocardiogram (ECG or EKG) Composite of all action potentials generated by nodal and contractile cells at given time Three waves: P wave – depolarization SA node  atria QRS complex - ventricular depolarization and atrial repolarization T wave - ventricular repolarization © 2013 Pearson Education, Inc.

Figure 18.17 An electrocardiogram (ECG) tracing.
Sinoatrial node Atrioventricular node QRS complex R Ventricular depolarization Ventricular repolarization Atrial depolarization T P Q S-T Segment P-R Interval S Q-T Interval 0.2 0.4 0.6 0.8 Time (s) © 2013 Pearson Education, Inc.

Figure The sequence of depolarization and repolarization of the heart related to the deflection waves of an ECG tracing. Slide 1 SA node R R P T P T Q S Q S Atrial depolarization, initiated by the SA node, causes the P wave. 1 Ventricular depolarization is complete. 4 R AV node R T P T P Q Q S S With atrial depolarization complete, the impulse is delayed at the AV node. Ventricular repolarization begins at apex, causing the T wave. 2 5 R R P T P T Q Q S S Ventricular repolarization is complete. 6 Ventricular depolarization begins at apex, causing the QRS complex. Atrial repolarization occurs. 3 Depolarization Repolarization © 2013 Pearson Education, Inc.

Atrial depolarization, initiated by the SA node, causes the P wave. 1
Figure The sequence of depolarization and repolarization of the heart related to the deflection waves of an ECG tracing. Slide 2 SA node R Depolarization Repolarization P T Q S Atrial depolarization, initiated by the SA node, causes the P wave. 1 © 2013 Pearson Education, Inc.

SA node R P T Q S 1 R AV node P T Q S 2
Figure The sequence of depolarization and repolarization of the heart related to the deflection waves of an ECG tracing. Slide 3 SA node R Depolarization Repolarization P T Q S Atrial depolarization, initiated by the SA node, causes the P wave. 1 R AV node P T Q S With atrial depolarization complete, the impulse is delayed at the AV node. 2 © 2013 Pearson Education, Inc.

SA node R P T Q S 1 R AV node P T Q S 2 R P T Q S 3
Figure The sequence of depolarization and repolarization of the heart related to the deflection waves of an ECG tracing. Slide 4 SA node R Depolarization Repolarization P T Q S Atrial depolarization, initiated by the SA node, causes the P wave. 1 R AV node P T Q S With atrial depolarization complete, the impulse is delayed at the AV node. 2 R P T Q S Ventricular depolarization begins at apex, causing the QRS complex. Atrial repolarization occurs. 3 © 2013 Pearson Education, Inc.

Ventricular depolarization is complete.
Figure The sequence of depolarization and repolarization of the heart related to the deflection waves of an ECG tracing. Slide 5 R Depolarization Repolarization P T Q S 4 Ventricular depolarization is complete. © 2013 Pearson Education, Inc.

Figure The sequence of depolarization and repolarization of the heart related to the deflection waves of an ECG tracing. Slide 6 R Depolarization Repolarization P T Q S 4 Ventricular depolarization is complete. R P T Q S Ventricular repolarization begins at apex, causing the T wave. 5 © 2013 Pearson Education, Inc.

Figure The sequence of depolarization and repolarization of the heart related to the deflection waves of an ECG tracing. Slide 7 R Depolarization Repolarization P T Q S 4 Ventricular depolarization is complete. R P T Q S Ventricular repolarization begins at apex, causing the T wave. 5 R P T Q S Ventricular repolarization is complete. 6 © 2013 Pearson Education, Inc.

Figure The sequence of depolarization and repolarization of the heart related to the deflection waves of an ECG tracing. Slide 8 SA node R R P T P T Q S Q S Atrial depolarization, initiated by the SA node, causes the P wave. 1 Ventricular depolarization is complete. 4 R AV node R T P T P Q Q S S With atrial depolarization complete, the impulse is delayed at the AV node. Ventricular repolarization begins at apex, causing the T wave. 2 5 R R P T P T Q Q S S Ventricular repolarization is complete. 6 Ventricular depolarization begins at apex, causing the QRS complex. Atrial repolarization occurs. 3 Depolarization Repolarization © 2013 Pearson Education, Inc.

Figure 18.19 Normal and abnormal ECG tracings.
Normal sinus rhythm. Junctional rhythm. The SA node is nonfunctional, P waves are absent, and the AV node paces the heart at 40–60 beats/min. Second-degree heart block. Some P waves are not conducted through the AV node; hence more P than QRS waves are seen. In this tracing, the ratio of P waves to QRS waves is mostly 2:1. Ventricular fibrillation. These chaotic, grossly irregular ECG deflections are seen in acute heart attack and electrical shock. © 2013 Pearson Education, Inc.

Two sounds (lub-dup) associated with closing of heart valves
Heart Sounds Two sounds (lub-dup) associated with closing of heart valves First as AV valves close; beginning of systole Second as SL valves close; beginning of ventricular diastole Pause indicates heart relaxation Heart murmurs - abnormal heart sounds; usually indicate incompetent or stenotic valves © 2013 Pearson Education, Inc.

heard in 2nd intercostal space at right sternal margin
Figure Areas of the thoracic surface where the sounds of individual valves can best be detected. Aortic valve sounds heard in 2nd intercostal space at right sternal margin Pulmonary valve sounds heard in 2nd intercostal space at left sternal margin Mitral valve sounds heard over heart apex (in 5th intercostal space) in line with middle of clavicle Tricuspid valve sounds typically heard in right sternal margin of 5th intercostal space © 2013 Pearson Education, Inc.

Mechanical Events: The Cardiac Cycle
Blood flow through heart during one complete heartbeat: atrial systole and diastole followed by ventricular systole and diastole Systole—contraction Diastole—relaxation Series of pressure and blood volume changes © 2013 Pearson Education, Inc.

Phases of the Cardiac Cycle
1. Ventricular filling—takes place in mid-to-late diastole AV valves are open; pressure low 80% of blood passively flows into ventricles Atrial systole occurs, delivering remaining 20% End diastolic volume (EDV): volume of blood in each ventricle at end of ventricular diastole © 2013 Pearson Education, Inc.

2. Ventricular systole Atria relax; ventricles begin to contract Rising ventricular pressure  closing of AV valves Isovolumetric contraction phase (all valves are closed) In ejection phase, ventricular pressure exceeds pressure in large arteries, forcing SL valves open End systolic volume (ESV): volume of blood remaining in each ventricle after systole © 2013 Pearson Education, Inc.

3. Isovolumetric relaxation - early diastole Ventricles relax; atria relaxed and filling Backflow of blood in aorta and pulmonary trunk closes SL valves Causes dicrotic notch (brief rise in aortic pressure as blood rebounds off closed valve) Ventricles totally closed chambers When atrial pressure exceeds that in ventricles  AV valves open; cycle begins again at step 1 © 2013 Pearson Education, Inc.

Volume of blood pumped by each ventricle in one minute
Cardiac Output (CO) Volume of blood pumped by each ventricle in one minute CO = heart rate (HR) × stroke volume (SV) HR = number of beats per minute SV = volume of blood pumped out by one ventricle with each beat Normal – 5.25 L/min © 2013 Pearson Education, Inc.

Cardiac Output (CO) At rest
CO (ml/min) = HR (75 beats/min)  SV (70 ml/beat) = 5.25 L/min CO increases if either/both SV or HR increased Maximal CO is 4–5 times resting CO in nonathletic people Maximal CO may reach 35 L/min in trained athletes Cardiac reserve - difference between resting and maximal CO © 2013 Pearson Education, Inc.

Chemical Regulation of Heart Rate
Hormones Epinephrine from adrenal medulla increases heart rate and contractility Thyroxine increases heart rate; enhances effects of norepinephrine and epinephrine Intra- and extracellular ion concentrations (e.g., Ca2+ and K+) must be maintained for normal heart function © 2013 Pearson Education, Inc.

Hypocalcemia  depresses heart Hypercalcemia  increased HR and contractility Hyperkalemia  alters electrical activity  heart block and cardiac arrest Hypokalemia  feeble heartbeat; arrhythmias © 2013 Pearson Education, Inc.

Other Factors that Influence Heart Rate
Age Fetus has fastest HR Gender Females faster than males Exercise Increases HR Body temperature Increases with increased temperature © 2013 Pearson Education, Inc.

Tachycardia - abnormally fast heart rate (>100 beats/min) If persistent, may lead to fibrillation Bradycardia - heart rate slower than 60 beats/min May result in grossly inadequate blood circulation in nonathletes May be desirable result of endurance training © 2013 Pearson Education, Inc.

Congestive heart failure (CHF) Progressive condition; CO is so low that blood circulation inadequate to meet tissue needs Reflects weakened myocardium caused by Coronary atherosclerosis—clogged arteries Persistent high blood pressure Multiple myocardial infarcts Dilated cardiomyopathy (DCM) © 2013 Pearson Education, Inc.

Pulmonary congestion Left side fails  blood backs up in lungs Peripheral congestion Right side fails  blood pools in body organs  edema Failure of either side ultimately weakens other Treat by removing fluid, reducing afterload, increasing contractility © 2013 Pearson Education, Inc.

Developmental Aspects of the Heart
Fetal heart structures that bypass pulmonary circulation Foramen ovale connects two atria Remnant is fossa ovalis in adult Ductus arteriosus connects pulmonary trunk to aorta Remnant - ligamentum arteriosum in adult Close at or shortly after birth © 2013 Pearson Education, Inc.

Developmental Aspects of the Heart
Congenital heart defects Most common birth defects; treated with surgery Most are one of two types: Mixing of oxygen-poor and oxygen-rich blood, e.g., septal defects, patent ductus arteriosus Narrowed valves or vessels  increased workload on heart, e.g., coarctation of aorta Tetralogy of Fallot Both types of disorders present © 2013 Pearson Education, Inc.

Figure 18.25 Three examples of congenital heart defects.
Narrowed aorta Occurs in about 1 in every 500 births Occurs in about 1 in every 1500 births Occurs in about 1 in every 2000 births Ventricular septal defect. The superior part of the inter-ventricular septum fails to form, allowing blood to mix between the two ventricles. More blood is shunted from left to right because the left ventricle is stronger. Coarctation of the aorta. A part of the aorta is narrowed, increasing the workload of the left ventricle. Tetralogy of Fallot. Multiple defects (tetra = four): (1) Pulmonary trunk too narrow and pulmonary valve stenosed, resulting in (2) hypertrophied right ventricle; (3) ventricular septal defect; (4) aorta opens from both ventricles. © 2013 Pearson Education, Inc.

Age-Related Changes Affecting the Heart
Sclerosis and thickening of valve flaps Decline in cardiac reserve Fibrosis of cardiac muscle Atherosclerosis © 2013 Pearson Education, Inc.

18 The Cardiovascular System: The Heart: Part A.

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18 The Cardiovascular System: The Heart: Part A.

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