C H A P T E R 19 The Heart The Heart A muscular double pump 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 The and Systemic Circuits arteries Venae cavae Circuit Capillary beds of lungs where gas exchange occurs veins and branches Left atrium atrium Heart Systemic Circuit Left Oxygen-rich, CO 2-poor blood Oxygen-poor, CO 2-rich blood Capillary beds of all body tissues where gas exchange occurs Figure 19.1 1
Location of the Heart in the Thorax Midsternal line Rib 2 Diaphragm Parietal pleura (cut) trunk Left lung Pericardium (cut) Apex of heart Diaphragm (c) (a) Mediastinum Mediastinum Heart lung (b) Posterior Superior vena cava auricle of right atrium (d) Left lung Fat in epicardium Rib 5 Pericardium (cut) Apex of heart Figure 19.2 Structure of the Heart Coverings Pericardium Fibrous pericardium strong layer of dense connective tissue Serous pericardium formed from two layers 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 2
Layers of the Pericardium and of the Heart Wall Pericardium Myocardium trunk Fibrous pericardium Parietal layer of serous pericardium Pericardial cavity Epicardium (visceral layer of serous pericardium) Myocardium Endocardium Heart wall Heart chamber Figure 19.3 Heart Chambers Internal divisions Atria and s Interventricular and interatrial septa External markings Coronary sulcus Anterior and posterior interventricular sulcus Gross Anatomy of the Heart Brachiocephalic trunk pulmonary Ascending aorta trunk Left common carotid Left subclavian Aortic arch Ligamentum arteriosum Left pulmonary Left pulmonary veins Auricle of pulmonary left atrium veins Circumflex atrium coronary Left coronary (in coronary sulcus) (in coronary sulcus) Anterior cardiac vein Left marginal Great cardiac vein Small cardiac vein Anterior interventricular (in anterior Inferior vena cava interventricular sulcus) (b) Anterior view Apex Figure 19.5b 3
Figure 19.5a Gross anatomy of the heart. Brachiocephalic trunk Left common carotid Left subclavian Aortic arch trunk Auricle of right atrium (a) Anterior aspect (pericardium removed) Auricle of left atrium Left Anterior interventricular sulcus Apex of heart (left ) Heart Chambers pulmonary trunk atrium pulmonary veins Fossa ovalis Pectinate muscles Tricuspid Chordae tendineae Trabeculae carneae Inferior vena cava Left pulmonary Left atrium Left pulmonary veins Mitral (bicuspid) Aortic Left Papillary muscle Interventricular septum Epicardium Myocardium Endocardium (e) Frontal section Figure 19.5e Figure 19.5f Gross anatomy of the heart. trunk auricle Tricuspid Chordae tendineae Papillary muscle ventricular myocardium (f) Photograph; view similar to (e) Brachiocephalic trunk Left common carotid Left subclavian Aortic arch Ligamentum arteriosum Left auricle Chordae tendineae of mitral Papillary muscle Interventricular septum Left ventricular myocardium Trabeculae carneae 4
Inferior View of the Heart Left pulmonary Left pulmonary veins Auricle of left atrium Left atrium Great cardiac vein Posterior vein of left Left pulmonary pulmonary veins atrium Inferior vena cava Coronary sinus coronary (in coronary sulcus) Posterior interventricular (in posterior interventricular sulcus) Middle cardiac vein Apex (d) Inferior view; surface shown rests on the diaphragm. Figure 19.5d Pathway of Blood Through the Heart Begin oxygen-poor blood in the superior and inferior venae cavae Go through pulmonary and systemic circuits 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 5
Blood Flow Through the Heart (SVC) Inferior vena cava (IVC) Coronary sinus atrium Tricuspid semilunar trunk SVC Coronary sinus atrium IVC Oxygen-poor blood To heart returns from the body tissues back to the heart. Tricuspid trunk semilunar Two pulmonary arteries carry the blood to the To lungs lungs (pulmonary circuit) to be oxygenated. arteries Oxygen-rich blood Oxygen-poor blood To body Oxygen-rich blood is delivered to the body tissues (systemic circuit). Oxygen-rich blood returns To heart to the heart via the four pulmonary veins. Aortic semilunar Aortic semilunar Left Mitral Left Mitral Left atrium veins Left atrium Four pulmonary veins Figure 19.10 Fibrous Skeleton Surrounds all four s Composed of dense connective tissue Functions Anchors cusps Prevents overdilation of openings Main point of insertion for cardiac muscle Blocks direct spread of electrical impulses Heart Valves Valve Structure Aortic Area of cutaway Mitral Tricuspid Myocardium Tricuspid (right atrioventricular) Mitral (left atrioventricular) Aortic Fibrous skeleton (a) Anterior Figure 19.6a 6
Function of the Atrioventricular Valves 1 Blood returning to the heart fills atria, putting pressure against atrioventricular s; atrioventricular s are forced open. 2 As s fill, atrioventricular flaps hang limply into s. 3 Atria contract, Ventricle forcing additional blood into s. (a) AV s open; atrial pressure greater than ventricular pressure Direction of blood flow Atrium Cusp of atrioventricular (open) Chordae tendineae Papillary muscle Figure 19.7a Function of the Atrioventricular Valves 1 Ventrles cicontract, forcing blood against atrioventricular cusps. 2 Atrioventricular s close. 3 Papillary muscles contract and chordae tendineae tighten, preventing flaps from everting into atria. (b) AV s closed; atrial pressure less than ventricular pressure Atrium Cusps of atrioventricular (closed) Blood in Figure 19.7b Function of the Semilunar Valves trunk As s contract and intraventricular pressure rises, blood is pushed up against semilunar s, forcing them open. (a) Semilunar s open As s relax and intraventricular pressure falls, blood flows back from arteries, filling the cusps of semilunar s and forcing them to close. (b) Semilunar s closed Figure 19.8 7
Heart Sounds Lub-dup sound of s closing First sound lub the AV s closing Second sound dup the semilunar s closing Heart Sounds Aortic Area of cutaway Mitral Tricuspid Myocardium Tricuspid (right atrioventricular) Mitral (left atrioventricular) Aortic Fibrous skeleton (a) Anterior Figure 19.6a Microscopic Anatomy of Cardiac Muscle Nucleus Intercalated discs Cardiac muscle cell Gap junctions Fasciae adherens (a) Cardiac muscle cell Intercalated t disc Mitochondrion Nucleus Mitochondrion T tubule Sarcoplasmic reticulum Z disc Nucleus Sarcolemma (b) I band A band I band Figure 19.12 8
Cardiac Muscle Tissue Intercalated discs complex junctions Adjacent sarcolemmas interlock Possess three types of cell junctions Desmosomes Fasciae adherans long desmosome-like junctions Gap junctions Heartbeat 70 80 beats/minute at rest Systole contraction Diastole expansion/relaxation Systole and diastole also refer to: Stage of heartbeat when s contract and expand Conducting System atrium 1 The sinoatrial (SA) node (pacemaker) generates impulses. Internodal pathway 2 The impulses pause (0.1 sec) at the atrioventricular (AV) node. 3 The atrioventricular (AV) bundle connects the atria to the s. Left atrium Purkinje fibers 4 The bundle branches conduct the impulses through the interventricular septum. 5 The Purkinje fibers stimulate the contractile cells of both s. Interventricular septum Figure 19.14 9
Innervation 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 The vagus nerve (parasympathetic) decreases heart rate. Sympathetic trunk ganglion SA node Parasympathetic fibers Sympathetic fibers Interneurons Cardioacceleratory center Dorsal motor nucleus of vagus Cardioinhibitory center Medulla oblongata Thoracic spinal cord Sympathetic trunk Sympathetic cardiac nerves increase heart rate and force of contraction. AV node Figure 19.15 Blood Supply to the Heart Functional blood supply Coronary arteries Arise from the aorta Located in the coronary sulcus Main branches Left and right coronary arteries Blood Supply to the Heart Superior vena cava trunk Left atrium Anastomosis (junction of Superior vessels) Left vena cava coronary atrium Circumflex Anterior Great cardiac cardiac coronary veins vein Left Coronary sinus Anterior marginal interventricular Posterior Small Middle cardiac vein interventricular cardiac vein (a) The major coronary arteries (b) The major cardiac veins Figure 19.16 10
Inferior View of the Heart Left pulmonary Left pulmonary veins Auricle of left atrium Left atrium Great cardiac vein Posterior vein of left Left pulmonary pulmonary veins atrium Inferior vena cava Coronary sinus coronary (in coronary sulcus) Posterior interventricular (in posterior interventricular sulcus) Middle cardiac vein Apex (d) Inferior view; surface shown rests on the diaphragm. Figure 19.5d Disorders of the Heart Coronary disease Atherosclerosis fatty deposits Angina pectoris chest pain Myocardial infarction blocked coronary Silent ischemia no pain or warning Disorders of the Heart Heart failure Progressive weakening of the heart Cannot meet the body s demands for oxygenated blood Congestive heart failure heart enlarges Pumping efficiency declines Cor pulmonale Enlargement and potential failure of the right 11
Disorders of Conduction Ventricular fibrillation Rapid, random firing of electrical impulses in the s Atrial fibrillation Multiple waves of impulses randomly signal the AV node Signals s to contract quickly and irregularly 12