1. ©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.

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

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

13. 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

14. 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.