©2012 Lippincott Williams & Wilkins. All rights reserved. ECG Workout: Chapter Review Chapter 1 Anatomy and physiology of the heart ©2012 Lippincott Williams & Wilkins. All rights reserved.

Description, location, and function of heart • Muscular organ • Average adult size is slightly larger than normal fist Location • Center of chest between lungs, behind sternum, in front of spine, and above diaphragm • Heart is tilted forward and leftward so right side is toward front • Top of heart (base) is just below 2nd rib • Bottom of heart (apex) is just below 5th rib; PMI palpated here • 2/3 of heart lies to left of body's midline; 1/3 to right Function • Functions primarily as pump to circulate blood through body • Can adjust pump performance to meet body's needs (if needs increase, heart rate increases; if needs decrease, heart rate decreases) 2

Heart surfaces Anterior - the front of the heart   Anterior - the front of the heart   Posterior - the back of the heart   Inferior - the bottom of the heart   Lateral - the side of the heart   3

Heart wall Pericardium – Serous pericardium The heart wall is composed of three layers: pericardium, myocardium, and endocardium. Pericardium Outer sac that covers and protects the heart Consists of: – Fibrous pericardium Tough, fibrous tissue Attached to lung, pleura, sternum, diaphragm, esophagus, trachea, and main bronchi Position anchors heart in chest – Serous pericardium Continuous membrane that forms two layers: Parietal layer - lines inner surface of fibrous pericardium Visceral layer (epicardium) - lines outer surface of myocardium Both layers separated by space (pericardial cavity) to allow room for heart to beat Both layers secrete fluid (10 to 30 mL) into pericardial space to lubricate and cushion the heart (continued) 4

Heart wall (continued) Myocardium Thick middle muscular layer Responsible for myocardial muscle contraction Endocardium Thin inner layer Lines heart's chambers and valves Rate: Normal (60 to 100 beats/minute) or slow (less than 60 beats/minute) 5

Circulatory system Systemic circuit Pulmonary circuit The circulatory system is a closed system consisting of heart chambers and blood vessels that provide a continuous flow of blood to the body. The circulatory system consists of two separate circuits. Systemic circuit Large circuit Includes left side of heart and blood vessels Carries oxygenated blood to body and deoxygenated blood back to right side of heart Pulmonary circuit Small circuit Includes right side of heart and blood vessels Carries deoxygenated blood to lungs and oxygenated blood back to left side of heart 6

Interior of the heart Heart chambers Chamber walls Septa The interior of the heart consists of four hollow chambers separated by walls (septa). Heart chambers Chamber walls Two upper chambers (the right atrium and the left atrium) receive incoming blood Thickness is related to amount of pressure needed to eject blood Atria - Blood-collecting reservoirs; low-pressure and thin walls Two lower chambers (the right ventricle and the left ventricle) pump blood out of heart Right ventricle - Pumps blood a short distance against low pressure to lungs; thicker wall than atria, but less than that of left ventricle Septa Interatrial septum separates the two atria Interventricular septum separates the two ventricles Left ventricle - Pumps blood a longer distance against high pressure in aorta; thickest wall Septa divide the heart into two pumping systems - right heart and left heart 7

Heart valves These structures open and close, through changes in chamber pressure, to allow a forward flow of blood and prevent a backflow (regurgitation) of blood. The heart has four valves: two atrioventricular (AV) valves and two semilunar valves. (continued) 8

Heart valves (continued) Atrioventricular (AV) valves (tricuspid and mitral) Both valves separate the atria from the ventricles Tricuspid valve - separates right atrium from right ventricle Mitral valve - separates left atrium from left ventricle AV leaflets are attached to fibrous cords (chordae tendineae), which then attach to papillary muscles arising from ventricular floor Structure of AV valves promotes blood flow into ventricles and prevents backflow of blood into atria during ventricular systole First heart sound (S1) is product of tricuspid and mitral valve closure Semilunar valves (pulmonic and aortic) Leaflets shaped like half-moons Pulmonic valve - separates right ventricle from pulmonary arteries Aortic valve - separates left ventricle from aorta Structure of leaflets (strength, close approximation, and shape) prevent backflow of blood into ventricles following ventricular contraction Second heart sound (S2) is product of aortic and pulmonic valve closure 9

Blood flow through heart and lungs Blood flow is traditionally described by tracing flow as blood returns from the systemic veins to the right side of the heart, out to the pulmonary circuit, back to the left side of the heart, and out to the arterial vessels of the systemic circuit. Right atrium Receives unoxygenated blood from superior vena cava, inferior vena cava, and coronary sinus Right atrial pressure increases, opening tricuspid valve and allowing blood to enter right ventricle Right ventricle Toward end of ventricular filling, left atrium contracts (atrial kick), pumping remaining 30% of blood into right ventricle (continued) 10

Blood flow through heart and lungs (continued) Right ventricle (continued) Left atrial pressure increases, opening mitral valve and allowing blood to enter left ventricle Right ventricular pressure increases, closing tricuspid valve and opening pulmonic valve Left ventricle Toward end of ventricular filling, left atrium contracts (atrial kick), pumping remaining 30% of blood into left ventricle Blood is ejected into pulmonary arteries and on to the lungs Lungs Left ventricular pressure increases, closing mitral valve and opening aortic valve Blood picks up oxygen; carbon dioxide is excreted Blood is ejected into aorta and to body Left atrium Receives oxygenated blood from lungs via pulmonary veins 11

Coronary blood supply Blood is supplied to the heart by the right coronary artery and the left coronary artery and their branches. (continued) 12

Coronary blood supply (continued) Right coronary artery Supplies right atrium and right ventricle - In 90% of population, supplies the inferior wall of left ventricle, posterior wall of left ventricle, posterior interventricular septum, AV node, and bundle of His In 55% of population, supplies SA node Dominant vessel in 90% of population Left coronary artery Left anterior descending (LAD) - Supplies anterior wall of left ventricle, anterolateral wall of left ventricle, anterior interventricular septum, and right and left bundle branches Circumflex - Supplies left atrium, anterolateral wall of left ventricle, and posterolateral wall of left ventricle - In 10% of population, supplies inferior wall of left ventricle, posterior wall of left ventricle, posterior interventricular septum, AV node, and bundle of His - In 45% of population, supplies SA node 13

Cardiac innervation Sympathetic nervous system The heart is under the control of the autonomic nervous system, which includes the sympathetic and parasympathetic nervous systems. Sympathetic nervous system Stimulation results in release of norepinephrine (a neurotransmitter), which increases heart rate, speeds conduction of impulses, and increases force of ventricular contraction. (Adrenergic receptors) Parasympathetic nervous system Stimulation results in release of acetylecholine (a neurotransmitter), which decreases heart rate, decreases conduction of impulses, and decreases force of ventricular contraction. (cholinergic receptors) In the normal heart, a balance is maintained between the accelerator effects of the sympathetic system and the inhibitory effects of the parasympathetic system.