The Human Heart

The heart is a muscular double pump Two functions Pulmonary circuit: Right side receives oxygen-poor blood from the body and pumps it to the lungs Systemic circuit: Left side receives oxygenated blood from lungs and pumps throughout the body 2

The Heart Atria Ventricles Receive blood from the pulmonary and systemic circuits Ventricles The pumping chambers of the heart 3

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

Figure 19.2 Location of the heart in the thorax. 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

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 6

Figure 19.3 The layers of the pericardium and of the heart wall. 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

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 8

Right and left ventricles Heart Chambers Right and left atria Superior chambers Right and left ventricles Inferior chambers Internal divisions Interventricular septa Interatrial septa 9

Figure 19.5b Gross anatomy of the heart. Left common carotid artery Brachiocephalic trunk Left subclavian artery Superior vena cava Aortic arch Ligamentum arteriosum Right pulmonary artery Left pulmonary artery Ascending aorta Pulmonary trunk Left pulmonary veins Auricle of left atrium Right pulmonary veins Circumflex artery Right atrium Right coronary artery (in coronary sulcus) Left 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 Apex Anterior view

Path of Blood Flow Through Heart

Forms right border of heart Right Atrium Forms right border of heart Receives oxygen-poor blood from systemic circuit through these vessels: Superior vena cava Inferior vena cava 12

Pumps blood into pulmonary circuit the pulmonary trunk Right Ventricle Receives blood from right atrium through the right atrioventricular valve (tricuspid valve) Pumps blood into pulmonary circuit the pulmonary trunk 13

Internal walls of right ventricle Trabeculae carneae Papillary muscles Chordae tendineae Pulmonary semilunar valve (pulmonary valve) Located at opening of right ventricle and pulmonary trunk Papillary muscle 14

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 Left atrioventricular valve (bicuspid valve) Mitral valve is another name for the left AV valve Bicuspid valve is another name for this. 15

Forms apex (lower tip) 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) 16

Figure 19.5e Gross anatomy of the heart. 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 Right ventricle Left ventricle Chordae tendineae Papillary muscle Interventricular septum Trabeculae carneae Epicardium Inferior vena cava Myocardium Endocardium Frontal section

Posterior View Aorta Superior vena cava Right pulmonary artery Left pulmonary artery Right pulmonary veins Left pulmonary veins Auricle of left atrium Right 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 Inferior view; surface shown rests on the diaphragm.

Heart Valves—Valve Structure Each valve composed of Endocardium with connective tissue core Atrioventricular (AV) valves Between atria and ventricles Right AV valve  tricuspid valve Left AV valve  bicuspid (mitral) valve Aortic and pulmonary valves At junction of ventricles and great arteries 19

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

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

Figure 19.8 Function of the semilunar valves. Aorta Pulmonary trunk As ventricles contract and intraventricular pressure rises, blood is pushed up against semilunar valves, forcing them open. 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. Semilunar valves closed

“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 23

Pathway of Blood Through Heart

Figure 19.10 The heart is a double pump, each side supplying its own circuit.

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 26

Structure of Heart Wall Walls differ in thickness Atria—thin walls Ventricles—thick walls Systemic circuit Longer than pulmonary circuit Offers greater resistance to blood flow 27

Structure of Heart Wall Left ventricle Three times thicker than right ventricle Exerts more pumping force Right ventricle Left ventricle Interventricular septum 28

Not all cardiac cells are innervated Cardiac Muscle Tissue Not all cardiac cells are innervated Will contract in rhythmic manner without innervation Inherent rhythmicity- autorhythmic 29

Conducting System- The heart is AUTORHYTHMIC!! Cardiac muscle tissue has intrinsic ability to Generate and conduct impulses Conducting system A series of specialized cardiac muscle cells 1. Sinoatrial (SA) node sets the inherent rate of contraction  INTERNODAL PATHWAY 2. Atrioventricular (AV) node  AV bundle  bundle branches  Purkinje Fibers 30

Figure 19.14 The intrinsic conducting system of the heart. (1 of 2) 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. Subendocardial conducting network (Purkinje fibers) 3 The atrioventricular (AV) bundle connects the atria to the ventricles. The bundle branches conduct the impulses through the interventricular septum. 4 Inter- ventricular septum 5 The subendocardial conducting network stimulates the contractile cells of both ventricles.

Innervation Heart rate is set by SA node but altered by 2 extrinsic mechanisms….

Innervation Parasympathetic fibers (Cardioinhibitory center in medulla of brain) Branches of vagus nerve Decrease heart rate Restricted to SA node, AV node, coronary arteries

Innervation Sympathetic nerves (Cardioacceleratory center in medulla of brain) Travel to heart from cervical and upper thoracic chain ganglia Innervate SA node, AV node, coronary arteries—as parasympathetic Also innervate cardiac musculature throughout the heart Increase heart rate and strength of contraction

Figure 19.15 Autonomic innervation of the heart. 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

Circulation to the heart…not by the heart Circulation to the heart…not by the heart. How does the heart itself get nutrients and oxygen?

Blood Supply to the Heart Coronary arteries Blood supply to the muscular walls and tissues of the heart Right coronary artery Left coronary artery Arise from base of the aorta and run in the coronary sulcus

Blood Supply to the Heart Left coronary artery (LCA) Branches into anterior interventricular artery and circumflex artery Left anterior descending artery (LAD) is the clinical name for anterior interventricular artery

Blood Supply to the Heart Right coronary artery (RCA) descends in coronary sulcus Branches to form the marginal artery Later braches into the posterior interventricular artery. Clinically called posterior descending artery (PDA)

Carry deoxygenated blood from the heart wall to the right atrium Cardiac Veins Carry deoxygenated blood from the heart wall to the right atrium Coronary sinus—runs in the posterior part of the coronary sulcus Returns majority of venous blood from the heart to the right atrium Three tributaries of coronary sinus Great cardiac vein, middle cardiac vein, small cardiac vein

Figure 19.16 Coronary circulation. 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

Coronary artery disease Disorders of the Heart Coronary artery disease Atherosclerosis—fatty deposits Angina pectoris—chest pain Myocardial infarction—blocked coronary artery Heart attack Silent ischemia—no pain or warning

Congestive heart failure (CHF) Disorders of the Heart Heart failure Progressive weakening of the heart Cannot meet the body’s demands for oxygenated blood Congestive heart failure (CHF) Heart enlarges Pumping efficiency declines Pulmonary arterial hypertension Enlargement and potential failure of right ventricle

Disorders of the Conduction System Arrythmias—variation from normal heart rhythm Ventricular fibrillation Rapid, random firing of electrical impulses in the ventricles Results from crippled conducting system Common cause of cardiac arrest

Disorders of the Conductory System Arrythmias (continued) Atrial fibrillation Impulses circle within atrial myocardium, stimulating AV node Promotes formation of clots Leads to strokes Occurs in episodes characterized by Anxiety, fatigue, shortness of breath, palpitations