19 PART 1 The Heart Pages 562-580

The Heart A muscular double pump Pulmonary circuit—takes blood to and from the lungs Systemic circuit—vessels transport blood to and from body tissues Atria—receive blood from the pulmonary and systemic circuits Ventricles—the pumping chambers of the heart

Figure 19.1 The heart as a double pump. Pulmonary Circuit Capillary beds of lungs where gas exchange occurs Aorta and branches Pulmonary arteries Left atrium Pulmonary veins Right atrium Heart Right ventricle Left ventricle Systemic Circuit Venae cavae Capillary beds of all body tissues where gas exchange occurs Oxygen-rich, CO2-poor blood Oxygen-poor, CO2-rich blood

Location and Orientation within the Thorax Heart—typically weighs 250–350 grams (healthy heart) Largest organ of the mediastinum Located between the lungs Apex lies to the left of the midline Base is the broad posterior surface

Location of the Heart in the Thorax Superior vena cava Left lung Aorta Parietal pleura (cut) Pericardium (cut) Pulmonary trunk Diaphragm Apex of heart Diaphragm (a) Rib 2 Midsternal line Pericardium (cut) Fat in epicardium Rib 5 Left lung Aorta Mediastinum Apex of heart (d) Right auricle of right atrium Superior vena cava ventricle Heart Posterior Right lung (b) Mediastinum Figure 19.2

Structure of the Heart—Coverings Pericardium—two primary layers Fibrous pericardium Strong layer of dense connective tissue Serous pericardium Formed from two layers Parietal layer of the serous pericardium Visceral layer of the serous pericardium

Layers of the Pericardium and of the Heart Wall Fibrous pericardium Parietal layer of serous pericardium Pericardial cavity Epicardium (visceral layer of serous pericardium) Myocardium Endocardium Pulmonary trunk Heart chamber Heart wall Pericardium Figure 19.3

Structure of the Heart—Layers of the Heart Wall Epicardium Visceral layer of the serous pericardium Myocardium Consists of cardiac muscle Muscle arranged in circular and spiral patterns Endocardium Endothelium resting on a layer of connective tissue Lines the internal walls of the heart

Right and left ventricles Internal divisions Heart Chambers Right and left atria Superior chambers Right and left ventricles Inferior chambers Internal divisions Interventricular septum Interatrial septum

Heart Chambers Aorta Left pulmonary artery Superior vena cava Left atrium Left pulmonary veins Mitral (bicuspid) valve Aortic valve Pulmonary valve Left ventricle Papillary muscle Interventricular septum Epicardium Myocardium Endocardium (e) Frontal section Superior vena cava Right pulmonary artery Pulmonary trunk Right atrium Right pulmonary veins Fossa ovalis Pectinate muscles Tricuspid valve Right ventricle Chordae tendineae Trabeculae carneae Inferior vena cava Figure 19.5e

Forms right border of heart Receives blood from systemic circuit Right Atrium Forms right border of heart Receives blood from systemic circuit Superior vena cava Inferior vena cava Coronary sinus Right auricle projects anteriorly from superior corner of atrium Opens into right ventricle via tricuspid valve (right atrioventricular valve)

Gross Anatomy of the Heart Left common carotid artery Left subclavian artery Aortic arch Ligamentum arteriosum Left pulmonary artery Left pulmonary veins Auricle of left atrium Circumflex artery Left coronary artery (in coronary sulcus) Left ventricle Great cardiac vein Anterior interventricular artery (in anterior interventricular sulcus) Apex (b) Anterior view Brachiocephalic trunk Superior vena cava Right pulmonary artery Ascending aorta Pulmonary trunk Right pulmonary veins Right atrium Right coronary artery Anterior cardiac vein Right ventricle Right marginal artery Small cardiac vein Inferior vena cava Figure 19.5b

Inferior View of the Heart (d) Inferior view; surface shown rests on the diaphragm. Aorta Left pulmonary artery Left pulmonary veins Auricle of left atrium Left atrium Great cardiac vein Posterior vein of left ventricle Left ventricle Apex Superior vena cava Right pulmonary artery Right pulmonary veins Right atrium Inferior vena cava Right coronary artery (in coronary sulcus) Coronary sinus Posterior interventricular artery (in posterior interventricular sulcus) Middle cardiac vein Right ventricle Figure 19.5d

Heart Chambers Aorta Left pulmonary artery Superior vena cava Left atrium Left pulmonary veins Mitral (bicuspid) valve Aortic valve Pulmonary valve Left ventricle Papillary muscle Interventricular septum Epicardium Myocardium Endocardium (e) Frontal section Superior vena cava Right pulmonary artery Pulmonary trunk Right atrium Right pulmonary veins Fossa ovalis Pectinate muscles Tricuspid valve Right ventricle Chordae tendineae Trabeculae carneae Inferior vena cava Figure 19.5e

Receives blood from right atrium through the tricuspid valve Right Ventricle Receives blood from right atrium through the tricuspid valve Pumps blood into pulmonary circuit via Pulmonary trunk Internal walls of right ventricle Trabeculae carneae Papillary muscles Chordae tendineae Pulmonary semilunar valve Located at opening of right ventricle and pulmonary trunk

Makes up heart’s posterior surface Left Atrium Makes up heart’s posterior surface Receives oxygen-rich blood from lungs through pulmonary veins Opens into the left ventricle through Mitral valve (left atrioventricular valve)

Inferior View of the Heart (d) Inferior view; surface shown rests on the diaphragm. Aorta Left pulmonary artery Left pulmonary veins Auricle of left atrium Left atrium Great cardiac vein Posterior vein of left ventricle Left ventricle Apex Superior vena cava Right pulmonary artery Right pulmonary veins Right atrium Inferior vena cava Right coronary artery (in coronary sulcus) Coronary sinus Posterior interventricular artery (in posterior interventricular sulcus) Middle cardiac vein Right ventricle Figure 19.5d

Gross Anatomy of the Heart Left common carotid artery Left subclavian artery Aortic arch Ligamentum arteriosum Left pulmonary artery Left pulmonary veins Auricle of left atrium Circumflex artery Left coronary artery (in coronary sulcus) Left ventricle Great cardiac vein Anterior interventricular artery (in anterior interventricular sulcus) Apex (b) Anterior view Brachiocephalic trunk Superior vena cava Right pulmonary artery Ascending aorta Pulmonary trunk Right pulmonary veins Right atrium Right coronary artery Anterior cardiac vein Right ventricle Right marginal artery Small cardiac vein Inferior vena cava Figure 19.5b

Heart Chambers Aorta Left pulmonary artery Superior vena cava Left atrium Left pulmonary veins Mitral (bicuspid) valve Aortic valve Pulmonary valve Left ventricle Papillary muscle Interventricular septum Epicardium Myocardium Endocardium (e) Frontal section Superior vena cava Right pulmonary artery Pulmonary trunk Right atrium Right pulmonary veins Fossa ovalis Pectinate muscles Tricuspid valve Right ventricle Chordae tendineae Trabeculae carneae Inferior vena cava Figure 19.5e

Internal walls of left ventricle Forms apex of the heart Internal walls of left ventricle Trabeculae carneae Papillary muscles Chordae tendineae Pumps blood through systemic circuit via Aortic semilunar valve (aortic valve)

Inferior View of the Heart (d) Inferior view; surface shown rests on the diaphragm. Aorta Left pulmonary artery Left pulmonary veins Auricle of left atrium Left atrium Great cardiac vein Posterior vein of left ventricle Left ventricle Apex Superior vena cava Right pulmonary artery Right pulmonary veins Right atrium Inferior vena cava Right coronary artery (in coronary sulcus) Coronary sinus Posterior interventricular artery (in posterior interventricular sulcus) Middle cardiac vein Right ventricle Figure 19.5d

Heart Chambers Aorta Left pulmonary artery Superior vena cava Left atrium Left pulmonary veins Mitral (bicuspid) valve Aortic valve Pulmonary valve Left ventricle Papillary muscle Interventricular septum Epicardium Myocardium Endocardium (e) Frontal section Superior vena cava Right pulmonary artery Pulmonary trunk Right atrium Right pulmonary veins Fossa ovalis Pectinate muscles Tricuspid valve Right ventricle Chordae tendineae Trabeculae carneae Inferior vena cava Figure 19.5e

Heart Valves—Valve Structure Each valve composed of Endocardium with connective tissue core Atrioventricular (AV) valves Between atria and ventricles Aortic and pulmonary valves At junction of ventricles and great arteries

Heart Valves—Valve Structure Pulmonary valve Aortic valve Area of cutaway Mitral valve Tricuspid valve Myocardium Tricuspid (right atrioventricular) valve (a) Mitral (left atrioventricular) Aortic Pulmonary Fibrous skeleton Anterior Figure 19.6a

Surrounds all four valves Fibrous Skeleton Surrounds all four valves Composed of dense connective tissue Functions Anchors valve cusps Prevents overdilation of valve openings Main point of insertion for cardiac muscle Blocks direct spread of electrical impulses

Function of the Atrioventricular Valves Blood returning to the heart fills atria, putting pressure against atrioventricular valves; atrioventricular valves are forced open. As ventricles fill, atrioventricular valve flaps hang limply into ventricles. Atria contract, forcing additional blood into ventricles. (a) AV valves open; atrial pressure greater than ventricular pressure Direction of blood flow Atrium Ventricle Cusp of valve (open) Chordae tendineae Papillary muscle 1 2 3 Figure 19.7a

Function of the Atrioventricular Valves Ventricles contract, forcing blood against atrioventricular valve cusps. Atrioventricular valves close. Papillary muscles contract and chordae tendineae tighten, preventing valve flaps from everting into atria. (b) AV valves closed; atrial pressure less than ventricular pressure Atrium Blood in ventricle Cusps of atrioventricular valve (closed) 1 2 3 Figure 19.7b

Function of the Semilunar Valves As ventricles contract and intraventricular pressure rises, blood is pushed up against semilunar valves, forcing them open. As ventricles relax pressure falls, blood flows back from arteries, filling the cusps of semilunar valves and forcing them to close. (a) Semilunar valves open (b) Semilunar valves closed Aorta Pulmonary trunk Figure 19.8

“Lub-dup”—sound of valves closing Heart Sounds “Lub-dup”—sound of valves closing First sound “lub” The AV valves closing Second sound “dup” The semilunar valves closing

Heart Sounds Pulmonary valve Aortic valve Area of cutaway Mitral valve Tricuspid valve Myocardium Tricuspid (right atrioventricular) valve (a) Mitral (left atrioventricular) Aortic Pulmonary Fibrous skeleton Anterior Figure 19.6a

Pathway of Blood Through the Heart Beginning with oxygen-poor blood in the superior and inferior venae cavae Go through pulmonary and systemic circuits A blood drop passes through all structures sequentially Atria contract together Ventricles contract together

Blood Flow Through the Heart Right atrium Aorta To body To heart To lungs Mitral valve Left ventricle Four pulmonary veins Superior vena cava (SVC) Inferior vena cava (IVC) Coronary sinus Pulmonary trunk arteries Aortic semilunar Tricuspid semilunar valve IVC SVC Two pulmonary arteries carry the blood to the lungs (pulmonary circuit) to be oxygenated. Oxygen-rich blood returns to the heart via the four pulmonary veins. Oxygen-poor blood returns from the body tissues back to the heart. Oxygen-rich blood is delivered to the body tissues (systemic circuit). Oxygen-rich blood Coronary sinus Figure 19.10

70–80 beats per minute at rest Heartbeat 70–80 beats per minute at rest Systole—contraction of a heart chamber Diastole—expansion of a heart chamber Systole and diastole also refer to Stage of heartbeat when ventricles contract and expand

Structure of Heart Wall Right ventricle Left Interventricular septum Walls differ in thickness Atria—thin walls Ventricles—thick walls Systemic circuit Longer than pulmonary circuit Offers greater resistance to blood flow Left ventricle— three times thicker than right Exerts more pumping force

Forms a thick layer called myocardium Cardiac Muscle Tissue Forms a thick layer called myocardium Striated like skeletal muscle Contractions pump blood through the heart and into blood vessels Contracts by sliding filament mechanism Cardiac muscle cells Short Branching Have one or two nuclei

Microscopic Anatomy of Cardiac Muscle Nucleus Intercalated discs Cardiac muscle cell (a) Fasciae adherens Gap junctions Nucleus I band A band Cardiac muscle cell Sarcolemma Z disc Mitochondrion T tubule Sarcoplasmic reticulum Intercalated disc (b) Figure 19.12

Cells join at intercalated discs Cardiac Muscle Tissue Cells join at intercalated discs Complex junctions Form cellular networks Cells are separated by delicate endomysium Binds adjacent cardiac fibers Contains blood vessels and nerves

Intercalated discs—complex junctions Cardiac Muscle Tissue Intercalated discs—complex junctions Adjacent sarcolemmas interlock Possess two distinct regions Fasciae adherens-bind adjacent cells together & transmit contractile force to them Gap junctions-allow ions to pass between cells & transmission of signals to adjacent cells

Triggered to contract by Ca2+ entering the sarcoplasm Cardiac Muscle Tissue Triggered to contract by Ca2+ entering the sarcoplasm Signals sarcoplasmic reticulum to release Ca2+ ions Ions diffuse into sarcomeres Trigger sliding filament mechanism

Cardiac muscle tissue has intrinsic ability to Conducting System Cardiac muscle tissue has intrinsic ability to Generate and conduct impulses Signal these cells to contract rhythmically Conducting system A series of specialized cardiac muscle cells Sinoatrial (SA) node sets the inherent rate of contraction

Conducting System The sinoatrial (SA) node (pacemaker) generates impulses. Internodal pathway Superior vena cava Right atrium Left atrium Purkinje fibers Inter- ventricular septum The impulses pause (0.1 sec) at the atrioventricular (AV) node. The atrioventricular (AV) bundle connects the atria to the ventricles. The bundle branches conduct the impulses through the interventricular septum. The Purkinje fibers stimulate the contractile cells of both ventricles. 1 2 3 4 5 Figure 19.14

Innervation Heart rate is altered by external controls Thoracic spinal cord The vagus nerve (parasympathetic) decreases heart rate. Cardioinhibitory center Cardio- acceleratory Sympathetic cardiac nerves increase heart rate and force of contraction. Medulla oblongata Sympathetic trunk ganglion Dorsal motor nucleus of vagus Sympathetic trunk AV node SA node Parasympathetic fibers Sympathetic fibers Interneurons Heart rate is altered by external controls Nerves to the heart include Visceral sensory fibers Parasympathetic branches of the vagus nerve Sympathetic fibers—from cervical and upper thoracic chain ganglia Figure 19.15

Blood Supply to the Heart Functional blood supply Coronary arteries Arise from the aorta Main branches Left and right coronary arteries

Blood Supply to the Heart Right ventricle coronary artery atrium marginal Posterior interventricular Anterior Circumflex Left Aorta Anastomosis (junction of vessels) Superior vena cava (a) The major coronary arteries Left atrium Pulmonary trunk cardiac veins Small cardiac vein Middle cardiac vein Great vein Coronary sinus (b) The major cardiac veins Figure 19.16