1. Chapter 20: The Heart

2. Homeostasis
Heart contributes to homeostasis by pumping blood throughout the body to deliver O2 & nutrients & remove wastes

3. Figure 20-2a The Location of the Heart in the Thoracic Cavity.
Trachea
Thyroid gland
First rib (cut)
Base of heart
Right lung
Left lung
Parietal pericardium (cut)
Apex of heart
Diaphragm a
An anterior view of the chest, showing the position of the heart and major blood vessels relative to the ribs, lungs, and diaphragm.

4. Figure 20-3a The Position and Superficial Anatomy of the Heart.
Base of heart 1 1
Ribs 2 2 3 3 4 4 5 5 6 6 7 7
Apex of heart 8 8 9 9 10 10 a
Heart position relative to the rib cage.

5. Figure 20-2b The Location of the Heart in the Thoracic Cavity.
Posterior mediastinum
Aorta (arch segment removed)
Esophagus
Left pulmonary artery
Right pleural cavity
Left pleural cavity
Right lung
Left lung
Bronchus of lung
Left pulmonary vein
Right pulmonary artery
Pulmonary trunk
Aortic arch
Right pulmonary vein
Left atrium
Left ventricle
Superior vena cava
Pericardial cavity
Right atrium
Epicardium
Right ventricle
Pericardial sac
Anterior mediastinum
Sternum b
A superior view of the organs in the mediastinum; portions of the lungs have been removed to reveal blood vessels and airways. The heart is located in the anterior part of the mediastinum, immediately posterior to the sternum.

6. Wrist (corresponds to base of heart)
Pericardium
Surrounds & protects heart
Fibrous pericardium
Dense irregular CT
Prevents overstretching of heart
Provides protection
Anchors heart in mediastinum
Serous pericardium
Parietal layer
Fused to fibrous pericardium
Visceral layer
Epicardium
In between is the pericardial cavity that contains pericardial fluid
Balloon c
Base of heart
Fibrous attachment to diaphragm
Cut edge of parietal pericardium
Fibrous tissue of pericardial sac
Parietal pericardium
Areolar tissue
Mesothelium
Cut edge of epicardium
Apex of heart
Wrist (corresponds to base of heart)
Inner wall (corresponds to epicardium)
Air space (corresponds to pericardial cavity)
Outer wall (corresponds to parietal pericardium)
The relationship between the heart and the pericardial cavity; compare with the fist-and-balloon example.

7. The Heart Wall
Myocardium (cardiac muscle tissue)
Pericardial cavity
Parietal pericardium
Dense fibrous layer
Cardiac muscle cells
Areolar tissue
Connective tissues
Mesothelium
Artery
Vein
Endocardium
Epicardium (visceral pericardium)
Endothelium
Areolar tissue
Mesothelium
Areolar tissue
Heart wall
Atrial musculature a
A diagrammatic section through the heart wall, showing the relative positions of the epicardium, myocardium, and endocardium. The proportions are not to scale; the thickness of the myocardial wall has been greatly reduced.
Ventricular musculature b
Cardiac muscle tissue forms concentric layers that wrap around the atria or spiral within the walls of the ventricles.

8. Figure 20-3b The Position and Superficial Anatomy of the Heart.
Left subclavian artery
Left common carotid artery
Arch of aorta
Ligamentum arteriosum
Brachiocephalic trunk
Ascending aorta
Descending aorta
Left pulmonary artery
Superior vena cava
Pulmonary trunk
Auricle of right atrium
Right atrium
Auricle of left atrium
Fat and vessels in anterior interventricular sulcus
Right ventricle
Fat and vessels in coronary sulcus
Left ventricle b
Major anatomical features on the anterior surface.

9. Figure 20-3c The Position and Superficial Anatomy of the Heart.
Left subclavian artery
Left common carotid artery
Ligamentum arteriosum
Brachiocephalic trunk
Left pulmonary artery
Ascending aorta
Pulmonary trunk
Superior vena cava
Auricle of left atrium
Auricle of right atrium
Left coronary artery (LCA)
Right atrium
Anterior interventricular sulcus
Right ventricle
Right coronary artery
Left ventricle
Coronary sulcus
Anterior interventricular branch of LCA
Marginal branch of right coronary artery c
Anterior surface of the heart, cadaver dissection.

10. Figure 20-3d The Position and Superficial Anatomy of the Heart.
Arch of aorta
Left pulmonary artery
Right pulmonary
artery
Left pulmonary veins
Fat and vessels in coronary sulcus
Superior
vena cava
Left atrium
Coronary sinus
Right pulmonary veins (superior and inferior)
Right atrium
Left ventricle
Inferior vena cava
Right ventricle
Fat and vessels in posterior interventricular sulcus d
Major landmarks on the posterior surface. Coronary arteries (which supply the heart itself) are shown in
red; coronary veins are shown in blue.

11. Figure 20-6a The Sectional Anatomy of the Heart.
Left common carotid artery
Brachiocephalic trunk
Left subclavian artery
Ligamentum arteriosum
Superior vena cava
Pulmonary trunk
Aortic arch
Pulmonary valve
Right pulmonary arteries
Left pulmonary arteries
Ascending aorta
Left pulmonary veins
Fossa ovalis
Left atrium
Opening of coronary sinus
Interatrial septum
Aortic valve
Right atrium
Cusp of left AV
(mitral) valve
Pectinate muscles
Conus arteriosus
Left ventricle
Cusp of right AV (tricuspid) valve
Chordae tendineae
Interventricular
septum
Papillary muscles
Trabeculae carneae
Right ventricle
Inferior vena cava
Moderator band
Descending aorta a
A diagrammatic frontal section through the heart, showing major landmarks and the path of blood flow (marked by arrows) through the atria, ventricles, and associated vessels.

12. Figure 20-6c The Sectional Anatomy of the Heart.
Left subclavian artery
Left common carotid artery
Brachiocephalic trunk
Superior vena cava
Pulmonary trunk
Ascending aorta
Cusp of pulmonary valve
Auricle of left atrium
Right atrium
Cusp of left AV (bicuspid) valve
Chordae tendineae
Papillary muscles
Cusps of right AV (tricuspid) valve
Left ventricle
Trabeculae carneae
Interventricular septum
Right ventricle c
Anterior view of a frontally sectioned heart showing internal features and valves.

13. Figure 20-7 Structural Differences between the Left and Right Ventricles.
Posterior interventricular sulcus
Left ventricle
Right ventricle
Right ventricle
Left ventricle
Fat in anterior interventricular sulcus
Dilated
Contracted a
A diagrammatic sectional view through the heart, showing the relative thicknesses of the two ventricles. Notice the pouchlike shape of the right ventricle and the greater thickness of the left ventricle. b
Diagrammatic views of the ventricles just before a contraction (dilated) and just after a contraction (contracted).

14. Figure 20-4b The Heart Wall.
Atrial musculature
Ventricular musculature b
Cardiac muscle tissue forms concentric layers that wrap around the atria or spiral within the walls of the ventricles.

15. Fibrous Skeleton Structural foundation for valves
Cardiac skeleton
Structural foundation for valves
Prevents overstretching of valves
Electrical insulator

16. Valves Ensure one-way flow of blood so that it does not backflow
Open & close in response to pressure changes as heart contracts & relaxes

17. Atrioventricular Valves
Chordae tendineae prevents valves from everting
Cardiac skeleton a
Transverse Sections, Superior View, Atria and Vessels Removed
POSTERIOR
RIGHT VENTRICLE
LEFT VENTRICLE
Left AV (bicuspid) valve (open)
Right AV (tricuspid) valve (open)
Aortic valve (closed)
Pulmonary valve (closed)
ANTERIOR
Relaxed ventricles
When the ventricles are relaxed, the AV valves are open and the semilunar valves are closed. The chordae tendineae are loose, and the papillary muscles are relaxed.
Pulmonary veins
LEFT ATRIUM
Chordae tendineae (loose)
Papillary muscles (relaxed)
LEFT VENTRICLE (relaxed and filling with blood)
Frontal Sections through Left Atrium and Ventricle
Aortic valve closed

18. Figure 20-6b The Sectional Anatomy of the Heart.
Chordae tendineae
Papillary muscles b
The papillary muscles and chordae tendineae support the right AV (tricuspid) valve. The photograph was taken from inside the right ventricle, looking toward a light shining from the right atrium.

19. Right AV (tricuspid) valve (closed) Left AV (bicuspid) valve (closed)
Semilunar Valves b
Contracting ventricles
When the ventricles are contracting, the AV valves are closed and the semilunar valves are open. In the frontal section notice the attachment of the left AV valve to the chordae tendineae and papillary muscles.
Aortic valve open
RIGHT VENTRICLE
LEFT VENTRICLE
Right AV (tricuspid) valve (closed)
Cardiac skeleton
Left AV (bicuspid) valve (closed)
Aortic valve (open)
Pulmonary valve (open)
Aorta
Aortic sinus
LEFT ATRIUM
Chordae tendineae (tense)
Papillary muscles (contracted)
Left ventricle (contracted)

20. Figure 20-1 An Overview of the Cardiovascular System.
Pulmonary Circuit
Systemic Circuit
Pulmonary arteries
Systemic arteries
Systemic veins
Pulmonary veins
Capillaries in head, neck, upper
limbs
Capillaries in lungs
Right atrium
Left atrium
Right ventricle
Left ventricle
Capillaries in trunk and lower
limbs

21. Blood Flow Through the Heart
15. Superior vena cava
5. Pulmonary trunk
Aortic arch
4. Pulmonary valve
6. Right pulmonary arteries
6. Left pulmonary arteries
13. Ascending aorta
8. Left pulmonary veins
7. Lungs
9. Left atrium
14. Systemic circulation
12. Aortic valve
1. Right atrium
10. Bicuspid valve
11. Left ventricle
2. Cusp of right AV (tricuspid) valve
3. Right ventricle
15. Inferior vena cava
Descending aorta

22. Coronary Circulation
Needed because nutrients would not diffuse fast enough from chambers to supply the heart wall
Coronary arteries
Right coronary artery
Atrial branches
R atrium
Posterior interventricular artery
ventricles
Marginal branch
R ventricle
Left coronary artery
Anterior interventricular artery
LAD
Circumflex branch
L ventricle & atrium
Coronary veins
Most drain into coronary sinus
Great cardiac vein
Middle cardiac vein
Small cardiac vein
Anterior cardiac veins

23. Figure 20-9 The Coronary Circulation.
Coronary sinus
Circumflex artery
Aortic arch
Left coronary
artery
Great cardiac vein
Marginal artery
Ascending aorta
Pulmonary trunk
Posterior interventricular artery
Circumflex artery
Right coronary artery
Posterior cardiac vein
Anterior interventricular artery
Atrial arteries
Small cardiac vein
Great cardiac vein
Left ventricle
Anterior cardiac veins
Right coronary artery
Small cardiac vein
Middle cardiac vein
Marginal artery b
Coronary vessels supplying and draining the posterior surface of the heart.
Marginal
artery a
Coronary vessels supplying and draining the anterior surface of the heart.
Left pulmonary veins
Left pulmonary
artery
Auricle of left atrium
Right pulmonary
artery
Circumflex artery
Superior vena cava
Great cardiac vein
Right pulmonary veins
Marginal artery
Posterior cardiac vein
Left atrium
Right atrium
Inferior vena cava
Coronary sinus
Middle cardiac vein
Right ventricle
Posterior interventricular artery c
A posterior view of the heart; the vessels have been injected with colored latex (liquid rubber).

24. Reperfusion of Heart
Reestablish blood flow after blockage of coronary artery
May damage tissue further due to formation of O2 free radicals
Causes cellular damage & death

25. Figure 20-10 Heart Disease and Heart Attacks.

26. Figure 20-5 Cardiac Muscle Cells.
Intercalated disc
Cardiac muscle
cell
Gap junction
Z-lines bound to opposing plasma membranes
Mitochondria
Intercalated disc (sectioned)
Desmosomes b
Structure of an intercalated disc
Nucleus
Cardiac muscle cell (sectioned)
Bundles of myofibrils
Intercalated discs a
Cardiac muscle cells
Cardiac muscle tissue
LM x 575 c
Cardiac muscle tissue

27. Figure 20-11 The Conducting System of the Heart.
Sinoatrial (SA) node
+20 mV
0 mV
Internodal pathways
−20 mV
Threshold
−40 mV
Atrioventricular (AV) node
−60 mV
Prepotential
AV bundle
0.8
1.6
Time (sec)
Bundle branches b
Changes in the membrane potential of a pacemaker
cell in the SA node that is establishing a heart rate of 72 beats per minute. Note the presence of a prepotential, a gradual spontaneous depolarization.
Purkinje fibers a
Components of the conducting system.

28. The Conducting System of the Heart
Sinoatrial (SA) node
Internodal pathways
Atrioventricular (AV) node
AV bundle
Bundle branches
Purkinje fibers
Components of the conducting system.
Specialized cardiac muscle fibers called autorhythmic fibers
Act as a pacemaker
Sets the rhythm

29. SA Node Changes in the membrane potential of a pacemaker
No stable resting potential
Threshold
Prepotential
Time (sec)
0.8
1.6
0 mV b
+20 mV
−20 mV
−40 mV
−60 mV
Changes in the membrane potential of a pacemaker
cell in the SA node that is establishing a heart rate of 72 beats per minute. Note the presence of a prepotential, a gradual spontaneous depolarization.

30. Figure 20-12 Impulse Conduction through the Heart.
SA node activity and atrial activation begin.
SA node
Time = 0 2
Stimulus spreads across the atrial surfaces and reaches the AV node.
AV node
Elapsed time = 50 msec 3
There is a 100-msec delay at the AV node. Atrial contraction begins.
AV bundle
Bundle branches
Elapsed time = 150 msec 4
The impulse travels along the interventricular septum within the AV bundle and the bundle branches to the Purkinje fibers and, by the moderator band, to the papillary muscles of the right ventricle.
Moderator band
Elapsed time = 175 msec 5
The impulse is distributed by Purkinje fibers and relayed throughout the ventricular myocardium. Atrial contraction is completed, and ventricular contraction begins.
Elapsed time = 225 msec
Purkinje fibers

31. Figure 20-15a The Action Potentials in Skeletal and Cardiac Muscle.3
Rapid Depolarization
The Plateau
Repolarization
Cause: Na+ entry
Duration: 3–5 msec
Ends with: Closure of voltage-gated fast sodium channels
Cause: Ca2+ entry
Duration: ∼175 msec
Ends with: Closure of slow calcium channels
Cause: K+ loss
Duration: 75 msec
Ends with: Closure of slow potassium channels
+30 2 1 mV
Relative refractory period 3
Absolute refractory period
−90
KEY
Absolute refractory period
100
200
300
Stimulus
Time (msec)
Relative refractory period a
Events in an action potential in a ventricular muscle cell.

32. Figure 20-15b The Action Potentials in Skeletal and Cardiac Muscle.
+30
Cardiac muscle
+30
Skeletal muscle
Action potential
Action potential mV mV
−85
−90
Tension
Tension
Contraction
Contraction
100
200
300
100
200
300
Time (msec)
Time (msec) b
Action potentials and twitch contractions in a skeletal muscle (above) and cardiac muscle (below). The shaded areas indicate the durations of the absolute (blue) and relative (beige) refractory periods.
KEY
Absolute refractory period
Relative refractory period

33. Table 20-1 Structural and Functional Differences between Cardiac Muscle Cells and Skeletal Muscle Fibers.

34. An Electrocardiogram Electrode placement for recording a standard ECG.
800 msec +1 R R a
Electrode placement for
recording a standard ECG.
P wave (atria depolarize)
T wave (ventricles repolarize)
S–T segment
+0.5
P–R segment
Millivolts Q S
S–T interval
P–R interval
Q–T interval
QRS interval (ventricles depolarize)
−0.5 b
An ECG printout is a strip of graph paper containing a record of the electrical events monitored by the electrodes. The placement of electrodes on the body surface affects the size and shape of the waves recorded. The example is a normal ECG; the enlarged section indicates the major components of the ECG and the measurements most often
taken during clinical analysis.

35. ECG Compare with normal readings & can determine
If conducting pathway is abnormal
If heart is enlarged
If certain regions of heart are damaged
Cause of chest pain

36. ECG Abnormalities Larger P waves Enlarged Q wave Enlarged R wave
Enlargement of atrium
Enlarged Q wave
May indicate MI
Enlarged R wave
Indicates enlarged ventricles
Flat T wave
Insufficient O2
Elevated T wave
hyperkalemia

37. Intervals or Segments P-Q interval S-T segment Q-T interval
Represents conduction time from beginning of atrial excitation to beginning of ventricular excitation
Lengthens when AP has to detour around scar tissue such as in CAD & rheumatic fever
S-T segment
Represents time when ventricular contractile fibers are depolarized
Elevated in acute MI
Depressed when insufficient O2
Q-T interval
Beginning of ventricular depolarization to end of ventricular repolarization
Lengthened by myocardial damage, myocardial ischemia, or conduction abnormalities

38. Figure 20-14 Cardiac Arrhythmias.

39. Systole
Phase of contraction
Diastole
Phase of relaxation

40. Cardiac Cycle All of the events in one heartbeat
Start a
Atrial systole begins:
Atrial contraction forces a small amount of additional blood into relaxed ventricles. b
Atrial systole ends, atrial diastole begins
0 msec
800 msec
100 msec
Cardiac cycle c
Ventricular systole— first phase: Ventricular contraction pushes AV valves closed but does not create enough pressure to open semilunar valves. f
Ventricular diastole—late:
All chambers are relaxed. Ventricles fill passively.
370 msec d
Ventricular systole— second phase: As ventricular pressure rises and exceeds pressure in the arteries, the semilunar valves open and blood is ejected. e
Ventricular diastole—early:
As ventricles relax, pressure in ventricles drops; blood flows back against cusps of semilunar valves and forces them closed. Blood flows into the relaxed atria.
All of the events in one heartbeat

41. Atrial Systole Atria are contracting while ventricles are relaxed
Atrial depolarization (P wave) causes atril contraction
Pressure inside increases on blood forcing blood through AV valves
End of atrial systole is also end of ventricular diastole
Volume of blood in ventricles at this time known as end-diastolic volume (EDV)

42. Ventricular Systole
Ventricles are contracting while atria are relaxing
As ventricles begin to contract, pressure rises causing AV valves to shut
Isovolumetric contraction – all 4 valves briefly closed
Pressure rises sharply causing semilunar valves to open
Ventricular ejection
Volume remaining in ventricle after ejection is end-systolic volume (ESV)
Stroke volume is volume ejected & is equal to EDV - ESV

43. Relaxation Period
As ventricles relax, pressure in chambers fall & blood in aorta & pulmonary trunk begins to backflow
Causes semilunar valves to close
Isovolumetric relaxation – period where all 4 valves closed
Ventricular pressure falls below atrial pressure & AV valves open
Ventricular filling begins

44. Figure 20-17 Pressure and Volume Relationships in the Cardiac Cycle.
ONE CARDIAC CYCLE
QRS complex
QRS complex
Electro- cardiogram (ECG) P T P
ATRIAL DIASTOLE
ATRIAL SYSTOLE
ATRIAL DIASTOLE
ATRIAL SYSTOLE
VENTRICULAR DIASTOLE
VENTRICULAR SYSTOLE
VENTRICULAR DIASTOLE
120 5
Aortic valve closes
Aortic valve opens 6
Aorta 90
Dicrotic notch 1
Atrial contraction begins.
Atria eject blood into ventricles.
Atrial systole ends; AV valves close.
Isovolumetric ventricular contraction.
Ventricular ejection occurs.
Semilunar valves close.
Isovolumetric relaxation occurs.
AV valves open; passive ventricular filling occurs. 2
Pressure (mm Hg) 60 3
Left ventricle 4 4 7 5 6 30
Left AV valve closes
Left AV valve opens 7
Left atrium 8 2 1 3 8
130
End-diastolic volume 3 2
Left ventricular volume (mL) 1
Stroke volume
End-systolic volume 6 50
100
200
300
400
500
600
700
800
Time (msec)

45. Semilunar valves close
Heart Sounds
Due to blood turbulence from valves closing
S1 due to AV valves
lubb
S2 due to semilunar valves
Dubb
S3 due to rapid ventricular filling
S4 due to turbulence during atrial systole
Aorta a
Semilunar valves open
Semilunar valves close
AV valves close
AV valves open
Left atrium
Left ventricle
120
Pressure (mm Hg) 90 60 30
Heart sounds S4
“Lubb”
“Dupp” S1 S2 S3
The relationship between heart sounds and key events in the cardiac cycle
Aortic valve
Sounds heard
Valve location
Pulmonary valve
Left AV valve
Right AV valve
Placements of a stethoscope for listening to the different sounds produced by individual valves b

46. Cardiac Output Volume of blood ejected each minute CO = SV x HR
At rest, it is typically about 5 liters (your blood volume)
Cardiac reserve is the difference between max CO & CO at rest

47. Figure 20-20 Factors Affecting Cardiac Output.
Factors Affecting Heart Rate (HR)
Factors Affecting Stroke Volume (SV)
Autonomic innervation
End-diastolic volume
End-systolic volume
Hormones
HEART RATE (HR)
STROKE VOLUME (SV) = EDV − ESV
CARDIAC OUTPUT (CO) = HR × SV

48. Regulation of Stroke Volume
Both L & R ventricles should pump out same volume of blood
Affected by
Preload
Degree of stretch on heart before it contracts
Contractility
Force of contraction
Afterload
Pressure that must be exceeded before ejection can occur

49. Preload
Within limits, the more it is stretched the more forcefully it will contract
So the more it fills, the more it stretches
Frank-Starling law of the heart
Proportional to EDV
Factors affecting EDV
Duration of ventricular diastole
Venous return

50. Contractility Positive inotropic agents increase contractility
Often promote Ca2+ inflow
Σ stimulation
Epi & NE
Increased Ca2+ in interstitial fluid
Digitalis
Negative inotropic agents decrease contractility
Reduce Ca2+ inflow
Inhibition of Σ stimulation
Anoxia
Acidosis
Some anesthetics
Increased K+ in interstitial fluid

51. Afterload Increased afterload causes SV to decrease Increased by HTN
Narrowing of arteries by atherosclerosis

52. Figure 20-23 Factors Affecting Stroke Volume.
Factors Affecting Stroke Volume (SV)
Venous return (VR)
Filling time (FT)
Increased by sympathetic stimulation
Decreased by parasympathetic stimulation
Increased by E, NE, glucagon, thyroid hormones
VR = EDV
FT = EDV
VR = EDV
FT = EDV
Contractility (Cont) of muscle cells
Preload
Cont = ESV
Increased by vasoconstriction
Decreased by vasodilation
Cont = ESV
Afterload (AL)
End-diastolic volume (EDV)
End-systolic volume (ESV)
AL = ESV
AL = ESV
STROKE VOLUME (SV)
EDV = SV
ESV = SV
EDV = SV
ESV = SV

53. Regulation of Heart Rate
ANS
Hormones

54. ANS Originates in cardiovascular center
Input provided by proprioceptors, chemoreceptors, & baroreceptors
Σ increases HR & force of contraction
PΣ decreases HR

55. Figure 20-21 Autonomic Innervation of the Heart.
Vagal nucleus
Cardioinhibitory
center
Cardioacceleratory center
Medulla
oblongata
Vagus (N X)
Spinal cord
Sympathetic
Parasympathetic
Parasympathetic preganglionic fiber
Sympathetic preganglionic fiber
Synapses in cardiac plexus
Sympathetic ganglia (cervical ganglia and superior thoracic ganglia [T1–T4])
Parasympathetic postganglionic fibers
Sympathetic postganglionic fiber
Cardiac nerve

56. Chemical HR decreased by Hormones Cations Hypoxia Acidosis Alkalosis
Epi & NE
Thyroid hormones
Cations K+
Elevated; decreases HR & force of contraction
Ca2+
Increased; increases HR & force of contraction
Na+
Increased; blocks Ca2+ & so decreases force of contraction

57. Others Also influenced by Age Gender Physical fitness Body temp
Newborn higher
Gender
Females higher
Physical fitness
lowers
Body temp
increases

58. Figure 20-24b A Summary of the Factors Affecting Cardiac Output.
Factors affecting heart rate (HR)
Factors affecting stroke volume (SV)
Skeletal muscle activity
Blood volume
Changes in peripheral circulation
Atrial reflex
Venous return
Filling time
Autonomic innervation
Hormones
Vasodilation or vasoconstriction
Preload
Contractility
Autonomic innervation
Hormones
End-diastolic volume
End-systolic volume
Afterload
HEART RATE (HR)
STROKE VOLUME (SV) = EDV − ESV
CARDIAC OUTPUT (CO) = HR × SV b
Factors affecting cardiac output