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The Heart

The Heart. Chapter 19. Introduction. The heart – a muscular double pump with two circuits: Pulmonary circuit — takes blood to and from the lungs Systemic circuit —vessels transport blood to and from body tissues Atria (‘entranceway’)—receive blood from the pulmonary and systemic circuits

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The Heart

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  1. The Heart Chapter 19

  2. Introduction • The heart – a muscular double pump with two circuits: • Pulmonary circuit— takes blood to and from the lungs • Systemic circuit—vessels transport blood to and from body tissues • Atria (‘entranceway’)—receive blood from the pulmonary and systemic circuits • Ventricles (‘hollow belly’)—the pumping chambers pumps blood around the two circuits • Heart pumps blood through 120,000 km (75,000 miles) of blood vessels (BVs) • Beats 100,000 times/day or 35 million times/year • Pumps 5 liters of blood/minute

  3. Capillary beds of lungs where gas exchange occurs Pulmonary Circuit Pulmonary arteries Pulmonary veins Aorta and branches Venae cavae Left atrium Right atrium Left ventricle 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 The Pulmonary and Systemic Circuits Figure 19.1

  4. Capillary beds of lungs where gas exchange occurs Pulmonary Circuit Pulmonary arteries Pulmonary veins Aorta and branches Venae cavae Left atrium Right atrium Left ventricle 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 Pulmonary and Systemic Circuits • Pulmonary Circuit: • Right side receives oxygen-poor blood from the body tissues • Pumps this blood to the lungs • Picks up O2 and dispels CO2 • Systemic Circuit: • Left side receives oxygen-rich blood returning from the lungs • Pumps this blood throughout the body • Supplies O2 and nutrients to the body tissues

  5. Superior vena cava Aorta Parietal pleura (cut) Pulmonary trunk Left lung Pericardium (cut) Apex of heart Diaphragm Mediastinum Aorta Superior vena cava Left lung Right auricle of right atrium Fat in epicardium Rib 5 Right ventricle Pericardium (cut) Apex of heart (Fig. 19.2) Location and Orientation within the Thorax • Heart: hollow and cone-shaped • Weighs 250–350 grams • About the size of your fist • Largest organ of the mediastinum • Located between the lungs • Apex lies to the left of the midline • Base is the broad posterior surface

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

  7. Midsternal line Rib 2 Diaphragm Mediastinum Heart Right lung Posterior Four “Corners” of the Heart • Imaginary lines connect 4 corner points • Delineates normal size and location • Superior right at costal cartilage of third rib and sternum • Inferior right at costal cartilage of sixth rib lateral to the sternum • Superior left at costal cartilage of second rib lateral to the sternum • Inferior left lies in the fifth intercostal space at the midclavicular line

  8. Clinical Connections – Cardiopulmonary Resuscitation (CPR) • The heart lies between two rigid structures, the vertebral column and the sternum • External pressure (compression) can be used to force blood out of the heart and into the circulation • If the heart suddenly stops beating: • CPR (properly applied cardiac compression) performed with artificial ventilation of the lungs (mouth-to-mouth respiration) can save lives • CPR keeps oxygenated blood circulating until the heart can be restarted

  9. Pericardium of the Heart—Coverings • Pericardium—triple-layered sac that encloses the heart • Two primary layers • Fibrouspericardium: strong layer of dense connective tissue • Serous pericardium: formed from two layers • Parietal layer of the serous pericardium • Visceral layer of the serous pericardium • Pericardial cavity – between the primary layers • Epithelial cells secrete lubricating serous fluid that reduces friction

  10. Three Layers of the Heart Wall • Epicardium: outer visceral layer of serous pericardium • Thin, transparent layer composed of mesothelium and CT • Myocardium: cardiac muscle, responsible for pumping action • Arranged in interlacing fibers that form two separate networks (atrial and ventricular) • Connected by intercalated discs (extensions of the sarcolemma) • Gap junctions link cardiac fibers and allow action potentials atrial and ventricular • Networks contract as a unit

  11. Layers of the Heart Wall • Endocardium: thin layer of simple squamous epithelium • Lines inside of the myocardium • Covers heart valves and tendons attached to the valves • Continuous with the epithelial lining of large blood vessels Epicardium Myocardium Endocardium

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

  13. Cardiac Muscle Bundles of the Myocardium • Myocardium organized in criss-crossing bundles of muscular beams • Muscle fibers (cells) – wrapped and bundled with CT sheaths (endomysium and perimysium) • Shorter in length and less circular in transverse section than skeletal • Branched so individual cardiac fibers have a ‘stair-step’ appearance • Ends of fibers connect to neighboring fibers by intercalated discs containing desmosomes (hold fibers together) and gap junctions • Mitochondria – larger and more numerous • Patern of thick and thin filaments similar to skeletal but T tubules are located over Z discs and the SR is smaller

  14. Cardiac muscle bundles Circular and Spiral Arrangements of Cardiac Muscle Bundles • Function to squeeze blood through the heart in the proper directions • Inferiorly through atria • Superiorly through ventricles Figure 19.4

  15. Heart Chambers • Right and left atria – superior chambers • Right and left ventricles – inferior chambers • Internal divisions – interventricular and interatrial septa • External markings • Coronary sulcus forms a crown encircling boundary between atria and ventricles • Anterior interventricular sulcus • Posterior interventricular sulcus

  16. Left common carotid artery Brachiocephalic trunk Left subclavian artery Aortic arch Superior vena cava 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 Left coronary artery (in coronary sulcus) Right coronary artery (in coronary sulcus) Anterior cardiac vein Left ventricle Right ventricle Great cardiac vein Right marginal artery Anterior interventricular artery (in anterior interventricular sulcus) Small cardiac vein Inferior vena cava (b) Anterior view Apex Gross Anatomy of the Heart Figure 19.5b

  17. Right Atrium • Forms right border of heart: receives oxygen-poor blood returning from systemic circuit via veins • Superior and inferior vena cava and coronary sinus • Pectinate muscles: ridges inside anterior of right atrium • Crista terminalis: landmark used to locate veins entering right atrium • Fossa ovalis: depression in interatrial septum • Remnant of foramen ovale of the fetal heart

  18. Right Ventricle • Receives blood from right atrium through the tricuspid valve or right atrioventricular (AV) valve • Pumps blood into pulmonary circuit via pulmonary trunk • Internal walls of right ventricle • Trabeculae carneae (‘little beams of flesh’) • Papillary muscles: attached to chordae tendineae • Chordae tendineae: bands attached to cusps of right AV valve • Pulmonary semilunar valve: located at opening of right ventricle and pulmonary trunk

  19. 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 (e) Frontal section Heart Chambers Figure 19.5e

  20. Left Atrium • Makes up heart’s posterior surface: receives oxygen-rich blood returning from lungs • Through two right and two left pulmonary veins • Opens into the left ventricle through the bicuspid or mitral valve (aka the left atrioventricular valve)

  21. Left Ventricle • Forms apex of the heart • Internal walls of left ventricle • Trabeculae carneae • Papillary muscles • Chordae tendineae: attached to cusps of left AV valve • Superiorly opens into the aorta • Pumps blood through systemic circuit via aortic semilunar valve (aortic valve)

  22. 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 (e) Frontal section Heart Chambers Figure 19.5e

  23. Aorta Superior vena cava Right pulmonary artery Left pulmonary artery Right pulmonary veins Left pulmonary veins Right atrium Auricle of left 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 (d) Inferior view; surface shown rests on the diaphragm. Inferior View of the Heart Figure 19.5d

  24. Fibrous Skeleton • Lies in the plane between the atria and ventricles • 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 from atria to ventricles • Critical for proper coordination of atrial and ventricular contractions

  25. Heart Valves—Valve Structure • Paired AV and semilunar valves enforce one-way flow of blood through the heart • Designed to prevent back flow in response to pressure changes in the heart chambers • Each valve composed of endocardium with core of connective tissue and contain two or three cusps • Atrioventricular (AV) valves lie between atria and ventricles • Right tricuspid valve (3 cusps) • Left bicuspid valve (2 cusps) • Aortic and pulmonary (semilunar) valves lie at the junction of the ventricles and great arteries

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

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

  28. 1 Ventrles contract, forcing blood against AV valve cusps. Atrium Cusps of AV valve (closed) 2 AV valves close. Papillary muscles Contract – chordaetendineae tighten, preventing valve flaps from everting into atria. 3 Blood in ventricle (b) AV valves closed; atrial pressure less than ventricular pressure Function of the Atrioventricular (AV) Valves • Contraction of ventricles force contained blood superiorly valves are pushed shut Figure 19.7b

  29. Aorta Pulmonary trunk As ventricles contract and intraventricular pressure rises, blood is pushed up against semilunar valves, forcing them open. (a) 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. (b) Semilunar valves closed Function of the Semilunar Valves • Ventricular contraction • Valves pushed open • Cusps flattened against artery walls • Ventricular relaxation • Backflowing blood closes valves Figure 19.8

  30. Heart Sounds • Closing of valves creates vibration in adjacent blood and heart walls • “Lub-dup” sound of valves closing • First sound “lub” produced by the AV valves closing at start of ventricular systole • Second sound “dup” produced by the semilunar valvesclosing at end of ventricular systole

  31. Heart Sounds • Each valve sound is best heard near a different heart corner • Pulmonary valve—superior left corner • Aortic valve—superior right corner • Mitral (bicuspid) valve—at the apex • Tricuspid valve—inferior right corner

  32. 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 Heart Sounds Figure 19.9

  33. Clinical Connection – Heart Valve Disorders • Stenosis (‘a narrowing) – of a heart valve opening that restrict blood flow • Insufficiency or incompetence – valve failure to close completely • Mitral stenosis – scar formation or congenital defect causes narrowing of the mitral valve • Mitral insufficiency – backflow of blood from the left ventricle • Mitral valve prolaspse (MVP): one or both cusps protrude into the left atrium during ventricular contraction • Aortic stenosis – aortic valve is narrowed • Aortic insufficiency – backflow of blood from the aorta into the left ventricle • Rheumatic fever – acute systemic inflammatory disease usually after a streptococcal infection of the throat • Antibodies produced to destroy the bacteria instead attack and inflame CTs in joints, heart valves, and other organs

  34. Capillary beds of lungs where gas exchange occurs Pulmonary Circuit Pulmonary arteries Pulmonary veins Aorta and branches Venae cavae Left atrium Right atrium Left ventricle 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 Pathway of Blood Through the Heart • Beginning with oxygen-poor blood from the superior and inferior venae cavae (coronary sinus) • Go through pulmonary and systemic circuits • A drop of blood passes through all structures sequentially • Atria contract together • Ventricles contract together

  35. Path of a Drop of Blood • Begin with oxygen-poor systemic blood as it arrives at the right side of the heart • Superior to the diaphragm enters the right atrium via the SVC • Body regions inferior to the diaphragm enters via the IVC • Heart wall blood is collected by and enters through the coronary sinus • Passes from the right atrium through the tricuspid (right AV) valve to the right ventricle • propelled by gravity and right atrium contraction • ventricle contracts propels blood through the pulmonary semilunar valve  pulmonary trunk  lungs through the pulmonary circuit for oxygenation

  36. Path of a Drop of Blood • Oxygenated blood returns via the 4 pulmonary veins to the left atrium through the mitral (bicuspid or left AV) valve • Into the left ventricle (propelled by gravity and left atrium contraction) • Left ventricle contraction propels blood through aortic semilunar valve  aorta and its branches • Delivers oxygen and nutrients to the body tissues through systemic capillaries • Oxygen-poor blood returns through the systemic veins to the right atrium • Whole cycle repeats continuously • Atria always contract together, followed by the simultaneous contraction of the ventricles

  37. Figure 18.6

  38. Figure 18.6b

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

  40. Heartbeat • Single sequence of atrial contraction followed by ventricular contraction • 70–80 beats per minute at rest • Systole—contraction of a heart chamber • Diastole—expansion of a heart chamber as chamber relaxes and fills with blood • Systole and diastole also refer to • Stage of heartbeat when ventricles contract and expand

  41. Structure of Heart Wall • Walls differ in thickness • Atria—thin walls • Ventricles—thick walls • Left ventricle generates more force and pumps blood at a higher pressure • Systemic circuit longer than pulmonary circuit • Offers greater resistance to blood flow

  42. Left ventricle Right ventricle Interventricular septum Structure of Heart Wall • Left ventricle—three times thicker than right • Exerts more pumping force • Flattens right ventricle into a crescent shape Figure 19.11

  43. Cardiac Muscle Tissue • Forms a thick layer called myocardium – contains cardiac muscle cells and connective tissue • Cardiac muscle cells short and branching with 1 or 2 nuclei • Cells joined at intercalated discs (complex junctions) • Striated like skeletal muscle • Contractions pump blood through the heart and into blood vessels • Contracts by sliding filament mechanism

  44. Cardiac Muscle Tissue • Intercalated discs – complex junctions that form cellular networks • Sarcolemmas of adjacent cells interlock through meshing ‘fingers’ • Contain fasciae adherens, long junctions bind adjacent cells and transmit contractile force • Contain gap junctions, allow ions to pass between cells, transmitting contractile signal to adjacent cells • Cells separated by delicateendomysium – binds adjacent cardiac fibers • Contains blood vessels and nerves

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

  46. Cardiac Muscle Tissue – Contraction • Triggered to contract by Ca2+ entering the sarcoplasm in response to an action potential • Rise in intracellular calcium signals sarcoplasmic reticulum to release stored Ca2+ ions • Ions diffuse into sarcomeres triggering sliding filament mechanism

  47. Cardiac Muscle Tissue • Not all cardiac cells are innervated • isolated cardiac cells contract in rhythmic manner • Inherent rhythmicity is the basis for rhythmic heartbeat

  48. 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 • carry impulses throughout heart musculature • Sinoatrial (SA) node sets the inherent rate of contraction

  49. Sequence that controls each heartbeat – atrial contraction followed by ventricular contraction • SA node – impulses spread along the cardiac fibers of the atria to signal the atria to contract some travel along an internodal pathway to the AV node 2. At the AV node impulses are delayed for a fraction of a second 3. Impulses race through the AV bundle (bundle of His) and enter the interventricular septum and divide 4. Right and left bundle branches (crura) 5. Purkinje fibers – halfway down the crura become subendocardial branches

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

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