19 The Heart

I. Circuits and Chambers The heart is a muscular double pump A. Pulmonary circuit: Right side receives oxygen-poor blood from the body and pumps it to the lungs B. Systemic circuit: Left side receives oxygenated blood from lungs and pumps throughout the body Atria = Receive blood from the pulmonary and systemic circuit Ventricles = Pump blood to the pulmonary and systemic circuit 2

Pulmonary Circuit Aorta and branches Pulmonary arteries Left atrium Pulmonary veins Right atrium Heart Right ventricle Left ventricle Systemic Circuit Venae cavae Oxygen-rich, CO2-poor blood Oxygen-poor, CO2-rich blood 3

II. Location and Orientation within the Thorax A. Healthy heart typically weighs 250–350 grams B. Largest organ of the mediastinum - located between the lungs C. Apex lies to the left of the midline D. Base is the broad posterior surface E. The Four “Corners” ► Superior right - at costal cartilage of third rib and sternum ► Inferior right - at costal cartilage of sixth rib lateral to sternum ► Superior left - at costal cartilage of second rib lateral to sternum ► Inferior left - lies in the fifth intercostal space 4

5 Superior vena cava Midsternal line Aorta Rib 2 Parietal pleura (cut) Diaphragm Pulmonary trunk Left lung Pericardium (cut) Mediastinum Apex of heart Heart Diaphragm Right lung T8 Posterior Mediastinum Aorta Superior vena cava Left lung Fat in epicardium Right auricle of right atrium Rib 5 Right ventricle Pericardium (cut) Apex of heart 5

III. Membranes of the Heart Pericardium - two primary layers A. fibrous pericardium - strong layer of dense connective tissue B. serous pericardium – reduces friction as heart beats 1. parietal layer = attached to the “wall” of cavity 2. visceral layer = attached to the heart surface (“organ”) 6

Parietal layer of serous pericardium Pulmonary trunk Fibrous pericardium Parietal layer of serous pericardium Pericardium Pericardial cavity Myocardium Epicardium (visceral layer of serous pericardium) Heart wall Myocardium Endocardium Heart chamber 7

IV. Layers of the Heart Wall A. Epicardium - visceral layer of the serous pericardium (“upon”) B. Myocardium - consists of cardiac muscle 1. cardiac muscle arranged in circular and spiral patterns C. Endocardium – inner surface 1. endothelium resting on a layer of connective tissue 2. lines the internal walls of the heart 3. Continuous with endothelium of arteries and veins 8

Cardiac muscle bundles 9

V. Heart Chambers A. Right and left atria - superior chambers B. Right and left ventricles - inferior chambers C. Internal divisions – septum wall between chambers 1. interventricular septa 2. interatrial septa 10

Auricle of left atrium Right atrium Left ventricle Right ventricle Apex Anterior view 11

VI. Right Atrium A. Forms right border of heart B. Receives oxygen-poor blood from systemic circuit through: 1. superior vena cava 2. inferior vena cava 3. coronary sinus (blood returning from veins of heart itself) C. Pectinate muscles - ridges inside anterior of right atrium D. Fossa ovalis - depression in interatrial septum 1. remnant of foramen ovale – hole between atria in fetal heart 12

VII. Right Ventricle A. Receives blood from right atrium through the right atrioventricular valve (tricuspid valve) B. Pumps blood into pulmonary circuit through pulmonary trunk C. Features of the internal walls of right ventricle ► trabeculae carneae – “fishnet like” small cavities ► chordae tendineae – “strings” attached to the valve cusps ► papillary muscles – attached to the chordae ► pectinate muscle – normal “smooth-like” muscle of walls D. Pulmonary semilunar valve (pulmonary valve) 1. Located at opening of right ventricle and pulmonary trunk 13

VIII. Left Atrium A. Forms the apex of the heart B. Makes up heart’s posterior surface C. Receives oxygen-rich blood from lungs through pulmonary veins D. Opens into the left ventricle through 1. left atrioventricular valve (bicuspid valve) a. mitral valve is another name for the left AV valve E. Pumps blood through systemic circuit via 1. aortic semilunar valve (aortic valve) 14

Brachiocephalic trunk Superior vena cava Right pulmonary artery Ascending aorta Pulmonary trunk Right pulmonary veins Right atrium Right ventricle Inferior vena cava Anterior view 15

Anterior view 16

Left common carotid artery Left subclavian artery Aortic arch Left pulmonary artery Left pulmonary veins Auricle of left atrium Left ventricle Apex Anterior view 17

Anterior view 18

Right atrium Right ventricle Fossa ovalis Pectinate muscles Tricuspid valve Right ventricle Chordae tendineae Trabeculae carneae Frontal section 19

Frontal section 20

Left atrium Left ventricle Left pulmonary veins Mitral (bicuspid) valve Aortic valve Pulmonary valve Left ventricle Papillary muscle Interventricular septum Frontal section 21

Frontal section 22

Inferior view; surface shown rests on the diaphragm. Auricle of left atrium Right atrium Left atrium Left ventricle Right ventricle Apex Inferior view; surface shown rests on the diaphragm. 23

IX. Heart Valves—Valve Structure A. Atrioventricular (AV) valves 1. between atria and ventricles Right AV valve  tricuspid valve Left AV valve  bicuspid (mitral) valve B. Aortic and pulmonary valves 1. at junction of ventricles and great arteries 24

Mitral (left atrioventricular) valve Pulmonary valve Aortic valve Area of cutaway Mitral valve Tricuspid valve Mitral (left atrioventricular) valve Tricuspid (right atrioventricular) valve Aortic valve Pulmonary valve Anterior 25

26 Direction of blood flow Atrium Cusp of atrioventricular valve (open) Chordae tendineae Papillary muscle Ventricle 26

X. Pathway of Blood Through the Heart superior/inferior vena cavae ► right atrium ► (tricsupid valve) ► right ventricle ► (pulmonary semilunar valve) ► pulmonary trunk ► LUNGS ► pulmonary veins ► left atrium ► (bicuspid (mitral) valve) ► left ventricle ► (aortic semilunar valve) ► aorta ► BODY 27

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XI. Structure of Heart Wall A. Walls differ in thickness 1. atria = thin walls; ventricles = thick walls 2. left ventricle 3X thicker than right ventricle a. exerts more pumping force (to the body!!) Left venticle 29

XII. Conduction System of the Heart A. Cardiac muscle cells have intrinsic ability to: 1. generate and conduct impulses 2. signal these cells to contract rhythmically SA node ► AV node ► AV Bundle (Bundle of His) ► Bundle branches ► Purkinje fibers 30

Inter- ventricular septum Right atrium sinoatrial (SA) node (pacemaker cells) atrioventricular (AV) node Left atrium atrioventricular (AV) bundle Inter- ventricular septum bundle branches Purkinje fibers 31

Inter- ventricular septum Right atrium Left atrium Inter- ventricular septum 32

XIII. Innervation of the Heart A. Parasympathetic fibers 1. branches of vagus nerve (X) 2. decrease heart rate 3. restricted to: SA node, AV node, coronary arteries B. Sympathetic nerves 1. travel from cervical and upper thoracic chain ganglia 2. also SA node, AV node, coronary arteries 3. also innervate cardiac muscle throughout the heart a. increase heart rate and strength of contraction

34 Dorsal motor nucleus of vagus The vagus nerve (parasympathetic) decreases heart rate. Cardioinhibitory center Cardioacceleratory center Medulla oblongata Sympathetic trunk ganglion Thoracic spinal cord Sympathetic trunk Sympathetic cardiac nerves increase heart rate and force of contraction. AV node SA node Parasympathetic fibers Sympathetic fibers Interneurons 34

XIV. Blood Supply to the Heart A. Coronary arteries 1. right coronary artery ► branches to form the marginal artery ► later branches into the posterior interventricular artery 2. left coronary artery ► anterior interventricular artery and circumflex artery

XV. Cardiac Veins A. carry deoxygenated blood from the heart wall to the right atrium B. occupy sulci (grooves) on the heart’s surface C. Coronary sinus—runs in the posterior part of the coronary sulcus 1. Returns majority of venous blood from heart to the right atrium D. Three tributaries of coronary sinus ► great cardiac vein ► middle cardiac vein ► small cardiac vein

Anastomosis (junction of vessels) Left atrium Superior vena cava Aorta Pulmonary trunk Anastomosis (junction of vessels) Left atrium Left coronary artery Right atrium Right coronary artery Circumflex artery Left ventricle Right ventricle Anterior interventricular artery Right marginal artery Posterior interventricular artery The major coronary arteries Superior vena cava Anterior cardiac veins Great cardiac vein Coronary sinus Small cardiac vein Middle cardiac vein The major cardiac veins 37