Anatomy Chapter 21: The Heart PDF

Chapter 21: The Heart  Introduction The heart keeps the blood in motion – If blood stops moving, nutrient and oxygen supplies are exhausted in the cells quickly The heart beats about 100,000 times per day – About 70 beats per minute The heart pumps about 1.5 million...

Chapter 21: The Heart  Introduction The heart keeps the blood in motion – If blood stops moving, nutrient and oxygen supplies are exhausted in the cells quickly The heart beats about 100,000 times per day – About 70 beats per minute The heart pumps about 1.5 million gallons of blood per year – About 2.9 gallons per minute The heart pumps between 5 and 30 liters of  An Overview of the Cardiovascular System The heart is about the size of a clenched fist The heart consists of four chambers – Two atria – Two ventricles The heart pumps blood into two circuits – Pulmonary circuit – Systemic circuit Figure 21.1 A Generalized View of the Pulmonary and Systemic Circuits Pulmonary Circuit Systemic Circuit Pulmonary arteries Systemic arteries Pulmonary veins Systemic veins Capillaries in head, neck, upper limbs Capillaries in lungs Left atrium Right atrium Right ventricle Left ventricle Capillaries in trunk and lower limbs  An Overview of the Cardiovascular System Each circuit involves arteries, veins, and capillaries – Arteries Transport blood away from the heart – Veins Transport blood toward the heart – Capillaries Vessels that interconnect arteries and veins  The Pericardium Pericardium is the serous membrane lining the pericardial cavity The pericardial membrane forms two layers – Visceral pericardium Also called the epicardium – Parietal pericardium The parietal pericardium is reinforced by a layer called the fibrous pericardium The parietal pericardium and fibrous Figure 21.2b Location of the Heart in the Thoracic Cavity Air space (corresponds to pericardial Cut edge of cavity) parietal pericardium Pericardial Cut edge of cavity containing epicardium pericardial fluid (visceral pericardium) Fibrous attachment to diaphragm Balloon b Relationships between the heart and the pericardial cavity. The pericardial cavity surrounds the heart like the balloon surrounds the fist (right).  Structure of the Heart Wall The walls of the heart consist of three layers: – Epicardium External surface – Myocardium Consists of cardiac muscle cells – Endocardium Internal surface of the chambers  Structure of the Heart Wall Cardiac Muscle Cells – Mostly dependent on aerobic respiration – The circulatory supply of cardiac muscle tissue is very extensive – Cardiac muscle cells contract without information coming from the CNS – Cardiac muscle cells are interconnected by intercalated discs Figure 21.3c Histological Organization of Muscle Tissue in the Heart Wall Intercalated disc Nucleus Cardiac muscle tissue LM × 575 c Histological view of cardiac muscle tissue. Distinguishing characteristics of cardiac muscle cells include (1) small size; (2) a single, centrally placed nucleus; (3) branching interconnections between cells; and (4) the presence of intercalated discs.  Structure of the Heart Wall The Intercalated Discs – Cardiac cells have specialized cell-to-cell junctions The sarcolemmae (plasma membranes) of two adjacent cardiac cells are bound together by desmosomes The intercalated discs bind the myofibrils of adjacent cells together Cardiac muscle cells are bound together by gap junctions – Ions move directly from one cell to another allowing all the muscle cells to contract as one unit Figure 21.3de Histological Organization of Muscle Tissue in the Heart Wall Cardiac muscle cell Mitochondria Intercalated disc (sectioned) Nucleus Cardiac muscle cell (sectioned) Gap junction Bundles of myofibrils Intercalated disc Z lines bound to opposing cell Intercalated membranes disc Desmosomes d Diagrammatic three-dimensional view of cardiac muscle cells. e The structure of an intercalated disc.  Structure of the Heart Wall The Fibrous Skeleton – Each cardiac cell is wrapped in an elastic sheath – Each muscle layer is wrapped in a fibrous sheet – The fibrous sheets separate the superficial layer from the deep layer muscles – These fibrous sheets also encircle the base of the pulmonary trunk and ascending aorta  Structure of the Heart Wall Functions of the Fibrous Skeleton – Stabilizes the position of cardiac cells – Stabilizes the position of the heart valves – Provides support for the blood vessels and nerves in the myocardium – Helps to distribute the forces of contraction – Helps to prevent overexpansion of the heart – Provides elasticity so the heart recoils  Orientation and Superficial Anatomy of Heart The heart lies slightly to the left of midline – Located in the mediastinum – The base is the superior portion of the heart – The apex is the inferior portion of the heart – The heart sits at an oblique angle – The right border is formed by only the right atrium – The inferior border is formed by the  Orientation and Superficial Anatomy of Heart The heart is rotated slightly toward the left – Basically, the heart appears to be twisted just a bit – The sternocostal surface is formed by the right atrium and right ventricle – The posterior surface is formed by the left atrium Figure 21.4 Position and Orientation of the Heart Superior border Base of heart 1 1 Ribs 2 2 3 3 4 4 Right border 5 5 Left border 6 6 7 7 Apex of 8 heart 8 9 9 10 10 Inferior border  Orientation and Superficial Anatomy of Heart The four chambers of the heart can be identified by sulci (grooves) on the external surface – Interatrial groove separates the left and right atria – Coronary sulcus separates the atria and the ventricles – Anterior interventricular sulcus separates the left and right ventricles – Posterior interventricular sulcus Figure 21.5a Superficial Anatomy of the Heart, Part I Left subclavian artery Left common carotid artery Arch of aorta Brachiocephalic trunk Ligamentum arteriosum Descending Ascending aorta aorta Left pulmonary Superior artery vena cava Pulmonary trunk Auricle of right Auricle of atrium RIGHT left atrium ATRIUM Fat in anterior RIGHT interventricular Fat in VENTRICLE LEFT sulcus coronary VENTRICLE sulcus a Anterior view of the heart and great vessels  Orientation and Superficial Anatomy of Heart The Left and Right Atria – Positioned superior to the coronary sulcus – Both have thin walls – Both consist of expandable extensions called auricles The Left and Right Ventricles – Positioned inferior to the coronary sulcus – Much of the left ventricle forms the diaphragmatic surface (in contact with Figure 21.5a Superficial Anatomy of the Heart, Part I Left subclavian artery Left common carotid artery Arch of aorta Brachiocephalic trunk Ligamentum arteriosum Descending Ascending aorta aorta Left pulmonary Superior artery vena cava Pulmonary trunk Auricle of right Auricle of atrium RIGHT left atrium ATRIUM Fat in anterior RIGHT interventricular Fat in VENTRICLE LEFT sulcus coronary VENTRICLE sulcus a Anterior view of the heart and great vessels  Internal Anatomy and Organization of the Heart A frontal section of the heart reveals: – Left and right atria separated by the interatrial septum – Left and right ventricles separated by the interventricular septum – The atrioventricular valves are formed from folds of endocardium (lining of the heart chambers) The atrioventricular valves are situated between the atria and the ventricles Figure 21.7b Sectional Anatomy of the Heart, Part I Left common carotid artery Brachiocephalic Left subclavian artery trunk Ligamentum arteriosum Superior Aortic arch Pulmonary trunk vena cava Pulmonary valve Right pulmonary Left pulmonary arteries arteries Ascending aorta Left pulmonary Fossa ovalis veins LEFT Opening of ATRIUM Interatrial septum coronary sinus Aortic valve RIGHT ATRIUM Cusp of left AV Pectinate muscles (mitral) valve Conus arteriosus LEFT VENTRICLE Cusp of right AV (tricuspid) valve Chordae tendineae Interventricular septum Papillary muscle Trabeculae carneae RIGHT VENTRICLE Inferior vena cava Moderator band Descending aorta b Diagrammatic frontal section through the relaxed heart shows the major landmarks and the path of blood flow through the atria and ventricles (arrows).  Internal Anatomy and Organization of the Heart The Right Atrium – Receives deoxygenated blood via the superior vena cava, inferior vena cava, and coronary sinus Coronary sinus enters the posterior side of the right atrium – Contains the fossa ovalis (fetal remnant of the foramen ovale)  Internal Anatomy and Organization of the Heart The Right Ventricle – Receives deoxygenated blood from the right atrium – Blood enters the ventricle by passing through the right atrioventricular (AV) valve or tricuspid valve – Blood leaves the ventricle by passing through the pulmonary valve Leads to the pulmonary trunk, then to the right and left pulmonary arteries  Internal Anatomy and Organization of the Heart The Right Ventricle – The right AV valve is connected to papillary muscles via chordae tendineae Since there are three cusps to the valve, the chordae tendineae are connected to three papillary muscles Papillary muscles and chordae tendineae prevent valve inversion when the ventricles contract Moderator band – Found only in the right ventricle – Muscular band that extends from the Figure 21.7b Sectional Anatomy of the Heart, Part I Left common carotid artery Brachiocephalic Left subclavian artery trunk Ligamentum arteriosum Superior Aortic arch Pulmonary trunk vena cava Pulmonary valve Right pulmonary Left pulmonary arteries arteries Ascending aorta Left pulmonary Fossa ovalis veins LEFT Opening of ATRIUM Interatrial septum coronary sinus Aortic valve RIGHT ATRIUM Cusp of left AV Pectinate muscles (mitral) valve Conus arteriosus LEFT VENTRICLE Cusp of right AV (tricuspid) valve Chordae tendineae Interventricular septum Papillary muscle Trabeculae carneae RIGHT VENTRICLE Inferior vena cava Moderator band Descending aorta b Diagrammatic frontal section through the relaxed heart shows the major landmarks and the path of blood flow through the atria and ventricles (arrows).  Internal Anatomy and Organization of the Heart The Left Atrium – Receives oxygenated blood from the lungs via the right and left pulmonary veins – Does not have pectinate muscles – Blood passes through the left atrioventricular (AV) valve or bicuspid valve Also called the mitral valve  Internal Anatomy and Organization of the Heart The Left Ventricle – Has the thickest wall Needed for strong contractions to pump blood throughout the entire systemic circuit Compare to the right ventricle, which has a thin wall since it only pumps blood through the pulmonary circuit – Does not have a moderator band – The LAV valve has chordae tendineae connecting to the two cusps and to two papillary muscles  Posterior interventricular sulcus Left ventricle Right ventricle Fat in anterior interventricular sulcus A diagrammatic sectional view through the heart, showing the relative thicknesses of the two ventricles. Notice the pouchlike shape of the right ventricle and the greater thickness of the left ventricle.  Right Left ventricle ventricle Dilated Contracted Diagrammatic views of the ventricles just before a contraction (dilated) and just after a contraction (contracted).  Internal Anatomy and Organization of the Heart The Left Ventricle (continued) – Blood leaves the left ventricle by passing through the aortic valve Blood enters the ascending aorta Blood then travels to the aortic arch and then to all body parts (systemic circulation) Figure 21.7b Sectional Anatomy of the Heart, Part I Left common carotid artery Brachiocephalic Left subclavian artery trunk Ligamentum arteriosum Superior Aortic arch Pulmonary trunk vena cava Pulmonary valve Right pulmonary Left pulmonary arteries arteries Ascending aorta Left pulmonary Fossa ovalis veins LEFT Opening of ATRIUM Interatrial septum coronary sinus Aortic valve RIGHT ATRIUM Cusp of left AV Pectinate muscles (mitral) valve Conus arteriosus LEFT VENTRICLE Cusp of right AV (tricuspid) valve Chordae tendineae Interventricular septum Papillary muscle Trabeculae carneae RIGHT VENTRICLE Inferior vena cava Moderator band Descending aorta b Diagrammatic frontal section through the relaxed heart shows the major landmarks and the path of blood flow through the atria and ventricles (arrows). Internal Anatomy and Organization Structural Differences between the Ventricles – Right ventricle Thinner wall Pouch shaped Weaker contraction – Left ventricle Thicker wall Round shape Powerful contraction--Six to seven times more powerful than the right ventricle  Internal Anatomy and Organization of the Heart Structure and Function of the Heart Valves – There are four valves in the heart Two AV valves – RAV/tricuspid and LAV/bicuspid/mitral valves Two semilunar valves – Aortic and pulmonary (pulmonic) valves  Internal Anatomy and Organization of the Heart Structure and Function of the Heart Valves – Each AV valve consists of four parts Ring of connective tissue – Connects to the heart tissue Cusps Chordae tendineae – Connect to the cusps and papillary muscles Papillary muscles – Contract in such a manner to prevent AV inversion Figure 21.9a Valves of the Heart Transverse Sections, Superior View, Atria and Vessels Removed Frontal Sections through Left Atrium and Ventricle POSTERIOR Fibrous Left AV (bicuspid) Pulmonary skeleton valve (open) veins RIGHT LEFT VENTRICLE LEFT VENTRICLE ATRIUM Ventricular Diastole Left AV (bicuspid) valve (open) Chordae Aortic valve tendineae (closed) (loose) Right AV (tricuspid) Papillary valve (open) muscles (relaxed) LEFT Aortic valve VENTRICLE (closed) (dilated) Pulmonary ANTERIOR valve (closed) a When the ventricles are relaxed, the AV valves are open and the semilunar valves are closed. The chordae tendineae are Aortic valve closed loose, and the papillary muscles are relaxed.  Internal Anatomy and Organization of the Heart Valve Function during the Cardiac Cycle – Papillary muscles relax – Due to the pressure in the atria, the AV valves open – When the ventricles contract, pressure causes the semilunar valves to open – Also upon contraction, the blood forces the AV valves closed, thus resulting in blood going through the semilunar valves Figure 21.9b Valves of the Heart Right AV Fibrous Left AV (tricuspid) valve skeleton (bicuspid) valve (closed) (closed) RIGHT LEFT Aorta LEFT VENTRICLE VENTRICLE ATRIUM Aortic sinus Left AV (bicuspid) Ventricular Systole Aortic valve valve (closed) (open) Chordae tendineae (tense) Papillary muscles (contracted) Aortic valve (open) Left ventricle (contracted) Pulmonary valve (open) b When the ventricles are contracting, the AV valves are closed and the semilunar valves are open. In the frontal section notice the attachment of the left AV valve to the chordae tendineae and papillary Aortic valve open muscles.  Coronary Blood Vessels Originate at the base of the ascending aorta – Supply the cardiac muscle tissue – Select coronary vessels: Right coronary artery (RCA) – Right marginal branch – Posterior interventricular branch Left coronary artery (LCA) – Circumflex branch – Left marginal branch – Anterior interventricular branch  Internal Anatomy and Organization of the Heart The Right Coronary Artery – Passes between the right auricle and pulmonary trunk – Has 4 major branches (you don’t need to know them) Figure 21.10a Coronary Circulation Left common carotid Left subclavian artery artery Brachiocephalic Aortic trunk arch Pulmonary trunk LEFT ATRIUM Left coronary Right artery (LCA) coronary artery Circumflex (RCA) branch of LCA Diagonal branch RIGHT of LCA ATRIUM Anterior interventricular branch of LCA Great cardiac vein LEFT Atrial RIGHT VENTRICLE branches VENTRICLE of RCA Small cardiac vein Anterior cardiac veins Marginal branch of RCA a Coronary vessels supplying the anterior surface of the heart.  Internal Anatomy and Organization of the Heart Left Coronary Artery – Major branches off the left coronary artery Circumflex branch – Branches to form the left marginal branch – Branches to form the posterior left ventricular branch Anterior interventricular branch – Branches that lead to the posterior interventricular branch called anastomoses Figure 21.10b Coronary Circulation Circumflex Atrial branch branch of LCA of LCA Great cardiac vein Marginal branch of LCA Posterior vein of left ventricle LEFT Posterior ATRIUM left ventricular branch of LCA Coronary sinus LEFT VENTRICLE RIGHT ATRIUM Small cardiac vein Right RIGHT coronary VENTRICLE artery (RCA) Right marginal branch of RCA Posterior interventricular Middle cardiac branch of RCA vein b Coronary vessels supplying the posterior surface of the heart.  Internal Anatomy and Organization of the Heart The Coronary Veins drain cardiac venous blood ultimately into the right atrium – Select coronary veins: Great cardiac vein – Delivers blood to the coronary sinus Middle cardiac vein – Delivers blood to the coronary sinus Small cardiac vein – Parallels the right coronary artery Coronary sinus – Drains directly into the posterior aspect of the right atrium Figure 21.10a Coronary Circulation Left common carotid Left subclavian artery artery Brachiocephalic Aortic trunk arch Pulmonary trunk LEFT ATRIUM Left coronary Right artery (LCA) coronary artery Circumflex (RCA) branch of LCA Diagonal branch RIGHT of LCA ATRIUM Anterior interventricular branch of LCA Great cardiac vein LEFT Atrial RIGHT VENTRICLE branches VENTRICLE of RCA Small cardiac vein Anterior cardiac veins Marginal branch of RCA a Coronary vessels supplying the anterior surface of the heart. Figure 21.10b Coronary Circulation Circumflex Atrial branch branch of LCA of LCA Great cardiac vein Marginal branch of LCA Posterior vein of left ventricle LEFT Posterior ATRIUM left ventricular branch of LCA Coronary sinus LEFT VENTRICLE RIGHT ATRIUM Small cardiac vein Right RIGHT coronary VENTRICLE artery (RCA) Right marginal branch of RCA Posterior interventricular Middle cardiac branch of RCA vein b Coronary vessels supplying the posterior surface of the heart. The Coordination of Cardiac Contractions The cardiac cycle consists of alternate periods of contraction and relaxation – Contraction is systole Blood is ejected into the ventricles Blood is ejected into the pulmonary trunk and the ascending aorta – Relaxation is diastole Chambers are filling with blood  The Coordination of Cardiac Contractions Cardiac contractions are coordinated by conducting cells There are two kinds of conducting cells – Nodal cells Sinoatrial node and atrioventricular node Establish the rate of contractions Cell membranes automatically depolarize – Conducting fibers Distribute the contractile stimulus to the myocardium The Sinoatrial and Atrioventricular Nodes Sinoatrial node (SA node) – Located in the posterior wall of the right atrium – Also called the cardiac pacemaker – Generates 80–100 action potentials per minute Atrioventricular node (AV node) – Sits within the floor of the right atrium – Generates 80–100 action potentials per minute – Upon exposure to acetylcholine (parasympathetic response), action potential slows down (bradycardia) – Upon exposure to norepinephrine (sympathetic response), action potential speeds up (tachycardia)  The Cardiac Cycle Summary of Cardiac Events – Impulse travels from the SA node to the AV node Atrial contraction occurs – Impulse travels from the AV node to the AV bundle – The AV bundle travels along the interventricular septum and then divides to form the right and left bundle branches – The bundle branches send impulses to Figure 21.11 The Conducting System and the Cardiac Cycle (3 of 8) Components of the Conducting System Sinoatrial contains pacemaker cells that initiate the electrical (SA) node impulse that results in a heartbeat Internodal are conducting fibers in the atrial wall that conduct pathways the impulse to the AV node while simultaneously stimulating cardiac muscle cells of both atria Atrioventricular slows the electrical impulse when it arrives from (AV) node the internodal pathways AV bundle conducts the impulse from the AV node to the bundle branches Left bundle extends toward the apex of the heart and then radiates branch across the inner surface of the left ventricle Right bundle extends toward the apex of the heart and then branch radiates across the inner surface of the right ventricle Moderator relays the stimulus through the ventricle to the band papillary muscles, which tense the chordae tendineae before the ventricles contract Purkinje convey the impulses very rapidly to the contractile fibers cells of the ventricular myocardium Figure 21.11 The Conducting System and the Cardiac Cycle (4 of 8) Movement of Electrical Impulses through the Conducting System 1 2 3 4 5 Time = 0 Elapsed time = 50 msec Elapsed time = 150 msec Elapsed time = 175 msec Elapsed time = 225 msec AV bundle Bundle Moderator Purkinje SA node AV node band branches fibers The SA node depolar- Depolarization spreads Atrial contraction begins. Impulses travel along the The impulse is distributed izes and atrial activa- across the atrial surfaces The AV node delays the AV bundle within the interven- by Purkinje fibers and tion begins. and reaches the AV node. spread of electrical tricular septum to the apex of relayed throughout the activity to the AV bundle the heart. Impulses also ventricular myocardium. by 100 msecs. spread to the papillary Atrial contraction is muscles of the right ventricle completed and ventricular by the moderator band. contraction begins. Figure 21.11 The Conducting System and the Cardiac Cycle (5 of 8) Atrial systole begins: Atrial Start contraction forces a small amount of blood into the relaxed ventricles. Atrial systole ends; atrial diastole begins: Atrial diastole continues until the start of the next cardiac cycle. 800 0 100 msec msec msec Ventricular systole— Cardiac first phase: Ventricular contraction pushes the cycle AV valves closed but does not create enough Ventricular diastole—late: pressure to open the All chambers are relaxed. semilunar valves. The AV valves open and the ventricles fill passively. 370 msec Ventricular systole— second phase: As ventricular pressure rises and exceeds the pressure in the arteries, the semilunar valves open Ventricular diastole—early: As the and blood is ejected. ventricles relax, the ventricular blood pressure drops until reverse blood flow pushes the cusps of the semilunar valves together. Blood now flows into the relaxed atria. Autonomic Control of Heart Rate The pacemaker sets the heart rate but can be altered – Impulses from the autonomic nervous system modify the pacemaker activity Nerves associated with the ANS innervate the: – SA node – AV node – Cardiac cells Autonomic Control of Heart Rate The effects of NE and ACh on nodal tissue – Norepinephrine from the ANS (sympathetic NS) causes: An increase in the heart rate An increase in the force of contractions – Acetylcholine from the ANS (parasympathetic NS) causes: A decrease in the heart rate A decrease in the force of contractions Autonomic Control of Heart Rate Cardiac centers in the medulla oblongata modify heart rate – Stimulation activates sympathetic neurons Cardioacceleratory center is activated Heart rate increases – Stimulation activates parasympathetic neurons CN X (vagus nerve) is involved Cardioinhibitory center is activated Heart rate decreases Figure 21.12 The Autonomic Innervation of the Heart Vagal nucleus Cardioinhibitory center Cardioacceleratory center Medulla oblongata Vagus nerve (N X) Spinal cord Sympathetic Parasympathetic Parasympathetic Sympathetic preganglionic preganglionic fiber fiber Synapses in Sympathetic ganglia cardiac plexus (cervical ganglia and Parasympathetic superior thoracic postganglionic ganglia [T1–T4]) fibers Sympathetic postganglionic fiber Cardiac nerve  Chapter 21 Summary Compare and contrast the pulmonary and systemic circuits Describe the anatomy of the pericardium and cardiac muscle Describe the orientation of the heart in the thoracic cavity Compare and contrast the anatomy of the four chambers of the heart Compare the anatomy of the right and left coronary arteries Outline the events of the cardiac cycle, including the role of nodal cells Outline how the heart rate is modified by the