Chapter 18 Lecture

1. CHAPTER 18: THE CARDIO-
VASCULAR SYSTEM: THE HEART
© 2013 Pearson Education, Inc.

2. Objectives
© 2013 Pearson Education, Inc.
I. Systemic vs. Pulmonary circuit
II. Heart Anatomy: Chambers and Valves
III. Blood Flow Through the Heart
IV. Cardiac Conduction System
V. Cardiac Cycle
VI. Fetal Heart Defects

3. © 2013 Pearson Education, Inc.
The Pulmonary and Systemic Circuits
• The heart is a transport system comprised
of two side-by-side pumps
– Right side receives oxygen-poor blood from
tissues
• Pumps to lungs to get rid of CO2, pick up O2, via
pulmonary (lung) circuit
– Left side receives oxygenated blood from
lungs
• Pumps to body tissues via systemic circuit

4. © 2013 Pearson Education, Inc.
The Pulmonary and Systemic Circuits
• Receiving chambers of heart:
– Right atrium
• Receives blood returning from systemic circuit
– Left atrium
• Receives blood returning from pulmonary circuit

5. © 2013 Pearson Education, Inc.
The Pulmonary and Systemic Circuits
• Pumping chambers of heart:
– Right ventricle
• Pumps blood through pulmonary circuit
– Left ventricle
• Pumps blood through systemic circuit

6. © 2013 Pearson Education, Inc.
Capillary beds of
lungs where gas
exchange occurs
Pulmonary Circuit
Pulmonary
arteries Pulmonary veins
Aorta and branches
Venae
cavae
Left
atrium
Left
ventricleRight
atrium
Right
ventricle
Heart
Systemic Circuit
Oxygen-rich,
CO2-poor blood
Oxygen-poor,
CO2-rich blood
Capillary beds of all
body tissues where
gas exchange occurs
Figure 18.1 The systemic and pulmonary circuits.

7. © 2013 Pearson Education, Inc.
http://www.youtube.com/watch?v=l7ejcLxKW8c
http://www.youtube.com/watch?v=QXckE_DlFAM
Heart Anatomy
• Approximately size of fist
• Location:
– In mediastinum between second rib and fifth
intercostal space
– On superior surface of diaphragm
– Two-thirds of heart to left of midsternal line
– Anterior to vertebral column, posterior to
sternum
PLAYPLAY

8. © 2013 Pearson Education, Inc.
Heart Anatomy
• Base (posterior surface) leans toward
right shoulder
• Apex points toward left hip
• Apical impulse palpated between fifth
and sixth ribs, just below left nipple

9. © 2013 Pearson Education, Inc.
Figure 18.2a Location of the heart in the mediastinum.
Midsternal line
2nd rib
Diaphragm
Sternum
Location of
apical impulse

10. © 2013 Pearson Education, Inc.
Figure 18.2b Location of the heart in the mediastinum.
Mediastinum
Heart
Right lung
Body of T7
vertebra
Posterior

11. © 2013 Pearson Education, Inc.
Figure 18.2c Location of the heart in the mediastinum.
Superior
vena cava
Pulmonary
trunk
Diaphragm
Aorta
Parietal pleura
(cut)
Left lung
Pericardium (cut)
Apex of heart

12. © 2013 Pearson Education, Inc.
Coverings of the Heart: Pericardium
• Double-walled sac
• Superficial fibrous pericardium
– Protects, anchors to surrounding structures,
and prevents overfilling

13. © 2013 Pearson Education, Inc.
Pericardium
• Deep two-layered serous pericardium –
recall the parietal pericardium and visceral
pericardium?
– Parietal layer lines internal surface of fibrous
pericardium
– Visceral layer (epicardium) on external
surface of heart
– The two layers are separated by the fluid-
filled pericardial cavity
– Serous fluid decreases friction

14. © 2013 Pearson Education, Inc.
Figure 18.3 The pericardial layers and layers of the heart wall.
Pericardium
Myocardium
Pulmonary
trunk Fibrous pericardium
Parietal layer of serous
pericardium
Pericardial cavity
Epicardium (visceral
layer of serous
pericardium)
Myocardium
Endocardium
Heart chamber
Heart
wall

15. © 2013 Pearson Education, Inc.
Homeostatic Imbalance
• Pericarditis
– Inflammation of pericardium
– Roughens membrane surfaces  pericardial
friction rub (creaking sound) heard with
stethoscope
– Cardiac tamponade
• Excess fluid builds up in the pericardial cavity and
sometimes compresses heart, causing limited
pumping ability

16. © 2013 Pearson Education, Inc.
Layers of the Heart Wall
• Three layers of heart wall:
– Epicardium
– Myocardium
– Endocardium
• Heart wall is richly vascularized
• Epicardium
– Visceral layer of serous pericardium

17. © 2013 Pearson Education, Inc.
Layers of the Heart Wall
• Myocardium - ‘muscle heart’ – 2nd
layer
– Spiral bundles of contractile cardiac muscle
cells
– Cardiac skeleton: crisscrossing, interlacing
layer of connective tissue
• Anchors cardiac muscle fibers
• Supports great vessels and valves
• Limits spread of action potentials to specific paths
as the connective tissue is not electrically
excitable.
• Links all parts of the heart together

18. © 2013 Pearson Education, Inc.
Layers of the Heart Wall
Endocardium – ‘inside the heart’ – 3rd
layer
• continuous with endothelial lining of blood
vessels
– Glistening white sheet of endothelium that
rests on a thin connective tissue layer
– Lines heart chambers; covers cardiac
skeleton of valves

19. © 2013 Pearson Education, Inc.
Figure 18.3 The pericardial layers and layers of the heart wall.
Pericardium
Myocardium
Pulmonary
trunk Fibrous pericardium
Parietal layer of serous
pericardium
Pericardial cavity
Epicardium (visceral
layer of serous
pericardium)
Myocardium
Endocardium
Heart chamber
Heart
wall

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Figure 18.4 The circular and spiral arrangement of cardiac muscle bundles in the myocardium of the heart.
Cardiac
muscle
bundles

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Chambers
• Four chambers:
– Two superior atria
– Two inferior ventricles
• Interatrial septum – separates atria
– Fossa ovalis – remnant of foramen ovale of
fetal heart
• Interventricular septum – separates
ventricles

22. © 2013 Pearson Education, Inc.
Figure 18.5e Gross anatomy of the heart.
Superior vena cava
Right pulmonary artery
Pulmonary trunk
Right atrium
Right pulmonary veins
Fossa ovalis
Pectinate muscles
Tricuspid valve
Right ventricle
Chordae tendineae
Trabeculae carneae
Inferior vena cava
Aorta
Left pulmonary artery
Left atrium
Left pulmonary veins
Mitral (bicuspid) valve
Aortic valve
Pulmonary valve
Left ventricle
Papillary muscle
Interventricular septum
Epicardium
Myocardium
Endocardium
Frontal section

23. © 2013 Pearson Education, Inc.
Chambers and Associated Great Vessels
• Coronary sulcus (atrioventricular groove)
– Encircles junction of atria and ventricles
• Anterior interventricular sulcus
– Anterior position of interventricular septum
• Posterior interventricular sulcus
– Landmark on posteroinferior surface

24. © 2013 Pearson Education, Inc.
Atria: The Receiving Chambers
• Auricles
– Appendages that increase atrial volume
• Right atrium
– Pectinate muscles
– Posterior and anterior regions separated by
crista terminalis
• Left atrium
– Pectinate muscles only in auricles

25. © 2013 Pearson Education, Inc.
Atria: The Receiving Chambers
• Small, thin-walled
• Contribute little to propulsion of blood
• Three veins empty into right atrium:
– Superior vena cava, inferior vena cava,
coronary sinus –
• Four pulmonary veins empty into left
atrium
• Which chamber receives deoxygenated
blood?

26. © 2013 Pearson Education, Inc.
Ventricles: The Discharging Chambers
• Most of the volume of heart
• Right ventricle - most of anterior surface
• Left ventricle – posteroinferior surface
• Trabeculae carneae – irregular ridges of
muscle on walls
• Papillary muscles – anchor chordae
tendineae

27. © 2013 Pearson Education, Inc.
Ventricles: The Discharging Chambers
• Thicker walls than atria
• Actual pumps of heart
• Right ventricle
– Pumps blood into pulmonary trunk
• Left ventricle
– Pumps blood into aorta (largest artery in
body)

28. © 2013 Pearson Education, Inc.
Figure 18.5b Gross anatomy of the heart.
Brachiocephalic trunk
Superior vena cava
Right pulmonary artery
Ascending aorta
Pulmonary trunk
Right pulmonary veins
Right atrium
Right coronary artery
(in coronary sulcus)
Anterior cardiac vein
Right ventricle
Right marginal artery
Small cardiac vein
Inferior vena cava
Left common carotid artery
Left subclavian artery
Aortic arch
Ligamentum arteriosum
Left pulmonary artery
Left pulmonary veins
Auricle of
left atrium
Circumflex artery
Left coronary artery
(in coronary sulcus)
Left ventricle
Great cardiac vein
Anterior interventricular
artery (in anterior
interventricular sulcus)
Apex
Anterior view

29. © 2013 Pearson Education, Inc.
Figure 18.5a Gross anatomy of the heart.
Aortic arch (fat covered)
Pulmonary trunk
Auricle of right atrium
Auricle of left atrium
Anterior interventricular
artery
Right ventricle
Apex of heart (left ventricle)
Anterior aspect (pericardium removed)

30. © 2013 Pearson Education, Inc.
Figure 18.5f Gross anatomy of the heart.
Photograph; view similar to (e)
Superior vena cava Ascending aorta (cut open)
Pulmonary trunk
Aortic valve
Pulmonary valve
Interventricular
septum (cut)
Left ventricle
Papillary muscles
Right ventricle anterior
wall (retracted)
Trabeculae carneae
Opening to right
atrium
Chordae tendineae
Right ventricle

31. © 2013 Pearson Education, Inc.
Heart Valves
• Ensure unidirectional blood flow through heart
• Open and close in response to pressure
changes
• Two atrioventricular (AV) valves
– Prevent backflow into atria when ventricles contract
– Tricuspid valve (right AV valve)
– Mitral valve (left AV valve, bicuspid valve)
– Chordae tendineae anchor cusps to papillary
muscles
• Hold valve flaps in closed position

32. © 2013 Pearson Education, Inc.
1
2
3
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.
1
2
3
Atria contract, forcing additional
blood into ventricles.
Ventricles contract, forcing
blood against AV valve cusps.
AV valves close.
Papillary muscles contract and
chordae tendineae tighten,
preventing valve flaps from everting
into atria.
AV valves open; atrial pressure greater than ventricular pressure
AV valves closed; atrial pressure less than ventricular pressure
Direction of
blood flow
Cusp of
atrioventricular
valve (open)
Atrium
Chordae
tendineae
Papillary
muscle
Atrium
Cusps of
atrioventricular
valve (closed)
Blood in
ventricle
Ventricle
Figure 18.7 The atrioventricular (AV) valves.

33. © 2013 Pearson Education, Inc.
Heart Valves
• Two semilunar (SL) valves
– Prevent backflow into ventricles when
ventricles relax
– Open and close in response to pressure
changes
– Aortic semilunar valve
– Pulmonary semilunar valve

34. © 2013 Pearson Education, Inc.
As ventricles contract
and intraventricular
pressure rises, blood
is pushed up against
semilunar valves,
forcing them open.
As ventricles relax
and intraventricular
pressure falls, blood
flows back from
arteries, filling the
cusps of semilunar
valves and forcing
them to close.
Aorta
Pulmonary
trunk
Semilunar valves open
Semilunar valves closed
Figure 18.8 The semilunar (SL) valves.

35. © 2013 Pearson Education, Inc.
Figure 18.6a Heart valves.
Pulmonary valve
Aortic valve
Area of cutaway
Mitral valve
Tricuspid valve
Myocardium
Mitral
(left atrioventricular)
valve
Tricuspid
(right atrioventricular)
valve
Aortic valve
Pulmonary valve
Anterior
Cardiac
skeleton

36. © 2013 Pearson Education, Inc.
Figure 18.6b Heart valves.
Pulmonary valve
Aortic valve
Area of cutaway
Mitral valve
Tricuspid valve
Myocardium
Mitral
(left atrioventricular)
valve
Tricuspid
(right atrioventricular)
valve
Aortic valve
Pulmonary valve

37. © 2013 Pearson Education, Inc.
Figure 18.6c Heart valves.
Pulmonary valve
Aortic valve
Area of cutaway
Mitral valve
Tricuspid valve
Chordae tendineae attached
to tricuspid valve flap
Papillary
muscle

38. © 2013 Pearson Education, Inc.
Figure 18.6d Heart valves.
Pulmonary valve
Aortic valve
Area of cutaway
Mitral valve
Tricuspid valve
Opening of inferior
vena cava
Tricuspid valve
Myocardium
of right
ventricle
Papillary
muscles
Mitral valve
Chordae
tendineae
Interventricular
septum
Myocardium
of left ventricle

39. Video Review of Blood Flow Through the
Heart and Heart Anatomy
© 2013 Pearson Education, Inc.
http://www.youtube.com/watch?v=7XaftdE_h60

40. © 2013 Pearson Education, Inc.
Homeostatic Imbalance
• Two conditions severely weaken heart:
– Incompetent or insufficient valve
• Blood backflows so heart repumps same blood
over and over
– Valvular stenosis
• Stiff flaps – constrict opening  heart must exert
more force to pump blood
• Valves become stiff due to calcium salt deposits or
scar tissue.
• Valve replaced with mechanical, animal,
or cadaver valve

41. © 2013 Pearson Education, Inc.
Pathway of Blood Through the Heart
• Pulmonary circuit
– Right atrium  tricuspid valve  right
ventricle
– Right ventricle  pulmonary semilunar valve
 pulmonary trunk  pulmonary arteries 
lungs
– Lungs  pulmonary veins  left atrium

42. © 2013 Pearson Education, Inc.
PLAYPLAY Animation: Rotatable heart (sectioned)
Pathway of Blood Through the Heart
• Systemic circuit
– Left atrium  mitral valve  left ventricle
– Left ventricle  aortic semilunar valve 
aorta
– Aorta  systemic circulation

43. © 2013 Pearson Education, Inc.
Figure 18.9 The heart is a double pump, each side supplying its own circuit.
Both sides of the heart pump at the same time, but let’s
follow one spurt of blood all the way through the
system.
Oxygen-rich blood
Superior vena cava (SVC)
Inferior vena cava (IVC)
Coronary sinus
Right
atrium
Tricuspid
valve
Pulmonary
Semilunar
valveRight
ventricle
Pulmonary
trunk
SVC
IVC
Coronary
sinus
Right
atrium
Tricuspid
valve
Right
ventricle
Pulmonary
arteries
Pulmonary
trunk
Pulmonary
semilunar
valve
To heart
Oxygen-poor blood
returns from the body
tissues back to the heart.
Oxygen-poor blood is carried
in two pulmonary arteries to
the lungs (pulmonary circuit)
to be oxygenated.
To lungs
Systemic
capillaries
Pulmonary
capillaries
To body
Oxygen-rich blood is
delivered to the body
tissues (systemic circuit).
Oxygen-rich blood returns
to the heart via the four
pulmonary veins.
To heart
Pulmonary
veins
Left
atrium
Mitral
valve
Left
ventricle
Aorta
Aortic
semilunar
valve
Aortic
Semilunar
valve
Mitral
valve
Aorta
Left
ventricle
Left
atrium
Four
pulmonary
veins
Oxygen-poor blood
Slide 1

44. © 2013 Pearson Education, Inc.
Oxygen-poor blood
Oxygen-rich blood
Superior vena cava (SVC)
Inferior vena cava (IVC)
Coronary sinus
SVC
IVC
Coronary
sinus
Slide 2Figure 18.9 The heart is a double pump, each side supplying its own circuit.

45. © 2013 Pearson Education, Inc.
Slide 3Figure 18.9 The heart is a double pump, each side supplying its own circuit.
Oxygen-poor blood
Oxygen-rich blood
Superior vena cava (SVC)
Inferior vena cava (IVC)
Coronary sinus
Right
atrium
SVC
IVC
Coronary
sinus
Right
atrium

46. © 2013 Pearson Education, Inc.
Figure 18.9 The heart is a double pump, each side supplying its own circuit. Slide 4
Oxygen-poor blood
Oxygen-rich blood
Superior vena cava (SVC)
Inferior vena cava (IVC)
Coronary sinus
Right
atrium
Tricuspid
valve Right
ventricle
SVC
IVC
Coronary
sinus
Right
atrium
Tricuspid
valve
Right
ventricle

47. © 2013 Pearson Education, Inc.
Figure 18.9 The heart is a double pump, each side supplying its own circuit. Slide 5
Oxygen-poor blood
Oxygen-rich blood
Superior vena cava (SVC)
Inferior vena cava (IVC)
Coronary sinus
Right
atrium
Tricuspid
valve
Pulmonary
Semilunar
valveRight
ventricle
Pulmonary
trunk
SVC
IVC
Coronary
sinus
Right
atrium
Tricuspid
valve
Right
ventricle
Pulmonary
arteries
Pulmonary
trunk
Pulmonary
semilunar
valve

48. © 2013 Pearson Education, Inc.
Figure 18.9 The heart is a double pump, each side supplying its own circuit. Slide 6
Oxygen-poor blood
Oxygen-rich blood
Superior vena cava (SVC)
Inferior vena cava (IVC)
Coronary sinus
Right
atrium
Tricuspid
valve
Pulmonary
Semilunar
valveRight
ventricle
Pulmonary
trunk
SVC
IVC
Coronary
sinus
Right
atrium
Tricuspid
valve
Right
ventricle
Pulmonary
arteries
Pulmonary
trunk
Pulmonary
semilunar
valve
Oxygen-poor blood is carried
in two pulmonary arteries to the
lungs (pulmonary circuit)
to be oxygenated.
To lungs
Pulmonary
capillaries

49. © 2013 Pearson Education, Inc.
Oxygen-poor blood
Oxygen-rich blood
Pulmonary
veins
Four
pulmonary
veins
Slide 7Figure 18.9 The heart is a double pump, each side supplying its own circuit.

50. © 2013 Pearson Education, Inc.
Figure 18.9 The heart is a double pump, each side supplying its own circuit. Slide 8
Pulmonary
veins
Left
atrium
Left
atrium
Four
pulmonary
veins
Blood Flow Through the Heart
Oxygen-poor blood
Oxygen-rich blood
Right
ventricle

51. © 2013 Pearson Education, Inc.
Figure 18.9 The heart is a double pump, each side supplying its own circuit. Slide 9
Oxygen-poor blood
Oxygen-rich blood
Pulmonary
veins
Left
atrium
Mitral
valve
Left
ventricle
Mitral
valveLeft
ventricle
Left
atrium
Four
pulmonary
veins

52. © 2013 Pearson Education, Inc.
Figure 18.9 The heart is a double pump, each side supplying its own circuit. Slide 10
Oxygen-poor blood
Oxygen-rich blood
Right
ventricle
Pulmonary
veins
Left
atrium
Mitral
valve
Left
ventricle
Aorta
Aortic
semilunar
valve
Aortic
Semilunar
valve
Mitral
valve
Aorta
Left
ventricle
Left
atrium
Four
pulmonary
veins

53. © 2013 Pearson Education, Inc.
Figure 18.9 The heart is a double pump, each side supplying its own circuit. Slide 11
Blood Flow Through the Heart
Systemic
capillaries
To body
Oxygen-rich blood is
delivered to the body
tissues (systemic
circuit).
Pulmonary
veins
Left
atrium
Mitral
valve
Left
ventricle
Aorta
Aortic
semilunar
valve
Aortic
Semilunar
valve
Mitral
valve
Aorta
Left
ventricle
Left
atrium
Four
pulmonary
veins
Oxygen-poor blood
Oxygen-rich blood

54. © 2013 Pearson Education, Inc.
Figure 18.9 The heart is a double pump, each side supplying its own circuit. Slide 12
Both sides of the heart pump at the same time, but let’s
follow one spurt of blood all the way through the
system.
Oxygen-rich blood
Superior vena cava (SVC)
Inferior vena cava (IVC)
Coronary sinus
Right
atrium
Tricuspid
valve
Pulmonary
Semilunar
valveRight
ventricle
Pulmonary
trunk
SVC
IVC
Coronary
sinus
Right
atrium
Tricuspid
valve
Right
ventricle
Pulmonary
arteries
Pulmonary
trunk
Pulmonary
semilunar
valve
To heart
Oxygen-poor blood
returns from the body
tissues back to the heart.
Oxygen-poor blood is carried
in two pulmonary arteries to
the lungs (pulmonary circuit)
to be oxygenated.
To lungs
Systemic
capillaries
Pulmonary
capillaries
To body
Oxygen-rich blood is
delivered to the body
tissues (systemic circuit).
Oxygen-rich blood returns
to the heart via the four
pulmonary veins.
To heart
Pulmonary
veins
Left
atrium
Mitral
valve
Left
ventricle
Aorta
Aortic
semilunar
valve
Aortic
Semilunar
valve
Mitral
valve
Aorta
Left
ventricle
Left
atrium
Four
pulmonary
veins
Oxygen-poor blood

55. © 2013 Pearson Education, Inc.
Pathway of Blood Through the Heart
• Equal volumes of blood pumped to pulmonary
and systemic circuits
• Pulmonary circuit short, low-pressure circulation
• Systemic circuit long, high-friction circulation;
encounters 5X more resistance to blood flow
than the pulmonary circulation.
• Anatomy of ventricles reflects differences
– Left ventricle walls 3X thicker than right
• Pumps with greater pressure

56. © 2013 Pearson Education, Inc.
Figure 18.10 Anatomical differences between the right and left ventricles.
Right
ventricle
Interventricular
septum
Left
ventricle

57. © 2013 Pearson Education, Inc.
Coronary Circulation
• Functional blood supply to heart muscle
itself
– Delivered when heart relaxed
– Left ventricle receives most blood supply
• Arterial supply varies among individuals
• Contains many anastomoses (junctions)
– Provide additional routes for blood delivery
– Cannot compensate for coronary artery
occlusion

58. © 2013 Pearson Education, Inc.
Coronary Circulation: Arteries
• Arteries arise from base of aorta
• Left coronary artery branches  anterior
interventricular artery and circumflex artery
– Supplies interventricular septum, anterior ventricular
walls, left atrium, and posterior wall of left ventricle
• Right coronary artery branches  right
marginal artery and posterior interventricular
artery
– Supplies right atrium and most of right ventricle

59. © 2013 Pearson Education, Inc.
Aorta
Superior
vena cava
Anastomosis
(junction of
vessels)
Right
atrium
Right
coronary
artery
Right
ventricle
Right
marginal
artery
Posterior
interventricular
artery
Anterior
interventricular
artery
Left
ventricle
Circumflex
artery
Left
coronary
artery
Left atrium
Pulmonary
trunk
The major coronary arteries
Figure 18.11a Coronary circulation.

60. © 2013 Pearson Education, Inc.
Coronary Circulation: Veins
• Cardiac veins collect blood from capillary beds
• Coronary sinus empties into right atrium;
formed by merging cardiac veins
– Great cardiac vein of anterior interventricular sulcus
– Middle cardiac vein in posterior interventricular
sulcus
– Small cardiac vein from inferior margin
• Several anterior cardiac veins empty directly
into right atrium anteriorly

61. © 2013 Pearson Education, Inc.
Figure 18.11b Coronary circulation.
Superior
vena cava
Anterior
cardiac
veins
Small
cardiac vein Middle cardiac vein
Coronary
sinus
Great
cardiac
vein
The major cardiac veins

62. © 2013 Pearson Education, Inc.
Figure 18.5d Gross anatomy of the heart.
Aorta
Left pulmonary artery
Left pulmonary veins
Auricle of left atrium
Left atrium
Great cardiac vein
Posterior vein of
left ventricle
Left ventricle
Apex
Superior vena cava
Right pulmonary artery
Right pulmonary veins
Right atrium
Inferior vena cava
Coronary sinus
Right coronary artery
(in coronary sulcus)
Posterior interventricular
artery (in posterior
interventricular sulcus)
Middle cardiac vein
Right ventricle
Posterior surface view

63. © 2013 Pearson Education, Inc.
Homeostatic Imbalances
• Angina pectoris
– Thoracic pain caused by fleeting deficiency in
blood delivery to myocardium
– Cells weakened
• Myocardial infarction (heart attack)
– Prolonged coronary blockage
– Areas of cell death repaired with
noncontractile scar tissue

64. © 2013 Pearson Education, Inc.
Microscopic Anatomy of Cardiac Muscle
• Cardiac muscle cells striated, short,
branched, fat, interconnected,
1 (perhaps 2) central nuclei
• Connective tissue matrix (endomysium)
connects to cardiac skeleton
– Contains numerous capillaries
• T tubules wide, less numerous; SR
simpler than in skeletal muscle
• Numerous large mitochondria (25–35% of
cell volume)

65. © 2013 Pearson Education, Inc.
Figure 18.12a Microscopic anatomy of cardiac muscle.
Nucleus
Intercalated
discs
Cardiac
muscle cell Gap junctions Desmosomes

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Microscopic Anatomy of Cardiac Muscle
• Intercalated discs - junctions between
cells - anchor cardiac cells
– Desmosomes prevent cells from separating
during contraction
– Gap junctions allow ions to pass from cell to
cell; electrically couple adjacent cells
• Allows heart to be functional syncytium
– Behaves as single coordinated unit

67. © 2013 Pearson Education, Inc.
Figure 18.12b Microscopic anatomy of cardiac muscle.
Cardiac muscle
cell
Intercalated
disc
Mitochondrion Nucleus
Mitochondrion
T tubule
Sarcoplasmic
reticulum Z disc
I band A band I band
Nucleus
Sarcolemma

68. Cardiac Conduction System
• is a group of specialized cardiac muscle
cells in the walls of the heart that send
signals to the heart muscle causing it to
contract. The main components of the
cardiac conduction system are the SA
node, AV node, bundle of His, bundle
branches, and Purkinje fibers.
© 2013 Pearson Education, Inc.

69. © 2013 Pearson Education, Inc.
Heart Physiology: Electrical Events
• Heart depolarizes and contracts without
nervous system stimulation
– Rhythm can be altered by autonomic nervous
system

70. © 2013 Pearson Education, Inc.
Heart Physiology: Setting the Basic Rhythm
• Coordinated heartbeat is a function of
– Presence of gap junctions
– Intrinsic cardiac conduction system
• Network of noncontractile (autorhythmic) cells
• Initiate and distribute impulses  coordinated
depolarization and contraction of heart

71. © 2013 Pearson Education, Inc.
Pacemaker (Autorhythmic) Cells
• Have unstable resting membrane potentials
(pacemaker potentials or prepotentials) due to
opening of slow Na+
channels
– Continuously depolarize
• At threshold, Ca2+
channels open
• Explosive Ca2+
influx produces the rising phase
of the action potential
• Repolarization results from inactivation of Ca2+
channels and opening of voltage-gated
K+
channels

72. © 2013 Pearson Education, Inc.
Action Potential Initiation by Pacemaker
Cells
• Three parts of action potential:
– Pacemaker potential
• Repolarization closes K+
channels and opens slow
Na+
channels  ion imbalance 
– Depolarization
• Ca2+
channels open  huge influx  rising phase
of action potential
– Repolarization
• K+
channels open  efflux of K+

73. © 2013 Pearson Education, Inc.
Figure 18.14 Pacemaker and action potentials of pacemaker cells in the heart. Slide 1
1
2
3
2
3
1
Membranepotential(mV)
+10
0
–10
–20
–30
–40
–50
–60
–70
Time (ms)
Action
potential
Threshold
Pacemaker
potential
1
2
3
Pacemaker potential This
slow depolarization is due to both
opening of Na+
channels and
closing of K+
channels. Notice
that the membrane potential is
never a flat line.
Depolarization The action
potential begins when the
pacemaker potential reaches
threshold. Depolarization is due
to Ca2+
influx through Ca2+
channels.
Repolarization is due to
Ca2+
channels inactivating and
K+
channels opening. This allows
K+
efflux, which brings the
membrane potential back to its
most negative voltage.

74. © 2013 Pearson Education, Inc.
Figure 18.14 Pacemaker and action potentials of pacemaker cells in the heart. Slide 2
1 1
+10
0
–10
–20
–30
–40
–50
–60
–70
Time (ms)
Action
potential
Threshold
Pacemaker
potential
1 Pacemaker potential This
slow depolarization is due to both
opening of Na+
channels and
closing of K+
channels. Notice
that the membrane potential is
never a flat line.
Membranepotential(mV)

75. © 2013 Pearson Education, Inc.
Figure 18.14 Pacemaker and action potentials of pacemaker cells in the heart. Slide 3
1
2 2
1
+10
0
–10
–20
–30
–40
–50
–60
–70
Time (ms)
Action
potential
Threshold
Pacemaker
potential
1
2
Pacemaker potential This
slow depolarization is due to both
opening of Na+
channels and
closing of K+
channels. Notice
that the membrane potential is
never a flat line.
Depolarization The action
potential begins when the
pacemaker potential reaches
threshold. Depolarization is due
to Ca2+
influx through Ca2+
channels.
Membranepotential(mV)

76. © 2013 Pearson Education, Inc.
Figure 18.14 Pacemaker and action potentials of pacemaker cells in the heart. Slide 4
1
2
3
2
3
1
Membranepotential(mV)
+10
0
–10
–20
–30
–40
–50
–60
–70
Time (ms)
Action
potential
Threshold
Pacemaker
potential
1
2
3
Pacemaker potential This
slow depolarization is due to both
opening of Na+
channels and
closing of K+
channels. Notice
that the membrane potential is
never a flat line.
Depolarization The action
potential begins when the
pacemaker potential reaches
threshold. Depolarization is due
to Ca2+
influx through Ca2+
channels.
Repolarization is due to
Ca2+
channels inactivating and
K+
channels opening. This allows
K+
efflux, which brings the
membrane potential back to its
most negative voltage.

77. © 2013 Pearson Education, Inc.
Sequence of Excitation
• Cardiac pacemaker cells pass impulses,
in order, across heart in ~220 ms
– Sinoatrial node 
– Atrioventricular node 
– Atrioventricular bundle 
– Right and left bundle branches 
– Subendocardial conducting network
(Purkinje fibers)

78. © 2013 Pearson Education, Inc.
Heart Physiology: Sequence of Excitation
• Sinoatrial (SA) node
– Pacemaker of heart in right atrial wall
• Depolarizes faster than rest of myocardium
– Generates impulses about 75X/minute (sinus
rhythm)
• Inherent rate of 100X/minute tempered by extrinsic
factors
• Impulse spreads across atria, and to AV
node

79. © 2013 Pearson Education, Inc.
Heart Physiology: Sequence of Excitation
• Atrioventricular (AV) node
– In inferior interatrial septum
– Delays impulses approximately 0.1 second
• Because fibers are smaller diameter, have fewer
gap junctions
• Allows atrial contraction prior to ventricular
contraction
– Inherent rate of 50X/minute in absence of
SA node input

80. © 2013 Pearson Education, Inc.
Heart Physiology: Sequence of Excitation
• Atrioventricular (AV) bundle
(bundle of His)
– In superior interventricular septum
– Only electrical connection between atria and
ventricles
• Atria and ventricles not connected via gap
junctions

81. © 2013 Pearson Education, Inc.
Heart Physiology: Sequence of Excitation
• Right and left bundle branches
– Two pathways in interventricular septum
– Carry impulses toward apex of heart

82. © 2013 Pearson Education, Inc.
Heart Physiology: Sequence of Excitation
• Subendocardial conducting network
– Complete pathway through interventricular
septum into apex and ventricular walls
– More elaborate on left side of heart
– AV bundle and subendocardial conducting
network depolarize 30X/minute in absence of
AV node input
• Ventricular contraction immediately follows
from apex toward atria

83. © 2013 Pearson Education, Inc.
Figure 18.15a Intrinsic cardiac conduction system and action potential succession during one heartbeat.
The sinoatrial (SA)
node (pacemaker)
generates impulses.
1
The impulses
pause (0.1 s) at the
atrioventricular
(AV) node.
2
The
atrioventricular
(AV) bundle
connects the atria
to the ventricles.
3
The bundle branches
conduct the impulses
through the
interventricular septum.
4
The subendocardial
conducting network
depolarizes the contractile
cells of both ventricles.
5
Superior vena cava Right atrium
Left atrium
Subendocardial
conducting
network
(Purkinje fibers)
Inter-
ventricular
septum
Anatomy of the intrinsic conduction system showing the sequence of
electrical excitation
Internodal pathway
Slide 1

84. © 2013 Pearson Education, Inc.
Figure 18.15a Intrinsic cardiac conduction system and action potential succession during one heartbeat.
The sinoatrial (SA)
node (pacemaker)
generates impulses.
1
Superior vena cava Right atrium
Left atrium
Subendocardial
conducting
network
(Purkinje fibers)
Inter-
ventricular
septum
Anatomy of the intrinsic conduction system showing the sequence of
electrical excitation
Slide 2
Internodal pathway

85. © 2013 Pearson Education, Inc.
Figure 18.15a Intrinsic cardiac conduction system and action potential succession during one heartbeat.
The sinoatrial (SA)
node (pacemaker)
generates impulses.
1
The impulses
pause (0.1 s) at the
atrioventricular
(AV) node.
2
Superior vena cava Right atrium
Left atrium
Subendocardial
conducting
network
(Purkinje fibers)
Inter-
ventricular
septum
Anatomy of the intrinsic conduction system showing the sequence of
electrical excitation
Slide 3
Internodal pathway

86. © 2013 Pearson Education, Inc.
Figure 18.15a Intrinsic cardiac conduction system and action potential succession during one heartbeat.
The sinoatrial (SA)
node (pacemaker)
generates impulses.
1
The impulses
pause (0.1 s) at the
atrioventricular
(AV) node.
2
The
atrioventricular
(AV) bundle
connects the atria
to the ventricles.
3
Superior vena cava Right atrium
Left atrium
Subendocardial
conducting
network
(Purkinje fibers)
Inter-
ventricular
septum
Anatomy of the intrinsic conduction system showing the sequence of
electrical excitation
Slide 4
Internodal pathway

87. © 2013 Pearson Education, Inc.
Figure 18.15a Intrinsic cardiac conduction system and action potential succession during one heartbeat.
The sinoatrial (SA)
node (pacemaker)
generates impulses.
1
The impulses
pause (0.1 s) at the
atrioventricular
(AV) node.
2
The
atrioventricular
(AV) bundle
connects the atria
to the ventricles.
3
The bundle branches
conduct the impulses
through the
interventricular septum.
4
Superior vena cava Right atrium
Left atrium
Subendocardial
conducting
network
(Purkinje fibers)
Inter-
ventricular
septum
Anatomy of the intrinsic conduction system showing the sequence of
electrical excitation
Slide 5
Internodal pathway

88. © 2013 Pearson Education, Inc.
Figure 18.15a Intrinsic cardiac conduction system and action potential succession during one heartbeat.
The sinoatrial (SA)
node (pacemaker)
generates impulses.
1
The impulses
pause (0.1 s) at the
atrioventricular
(AV) node.
2
The
atrioventricular
(AV) bundle
connects the atria
to the ventricles.
3
The bundle branches
conduct the impulses
through the
interventricular septum.
4
The subendocardial
conducting network
depolarizes the contractile
cells of both ventricles.
5
Superior vena cava Right atrium
Left atrium
Subendocardial
conducting
network
(Purkinje fibers)
Inter-
ventricular
septum
Anatomy of the intrinsic conduction system showing the sequence of
electrical excitation
Slide 6
Internodal pathway

89. © 2013 Pearson Education, Inc.
Mechanical Events: The Cardiac Cycle
• Cardiac cycle
– Blood flow through heart during one complete
heartbeat: atrial systole and diastole followed
by ventricular systole and diastole
– Systole—contraction
– Diastole—relaxation
– Series of pressure and blood volume changes

90. © 2013 Pearson Education, Inc.
Phases of the Cardiac Cycle
• 1. Ventricular filling—takes place in mid-
to-late diastole
– AV valves are open; pressure low
– 80% of blood passively flows into ventricles
– Atrial systole occurs, delivering remaining
20%
– End diastolic volume (EDV): volume of
blood in each ventricle at end of ventricular
diastole

91. © 2013 Pearson Education, Inc.
Phases of the Cardiac Cycle
• 2. Ventricular systole
– Atria relax; ventricles begin to contract
– Rising ventricular pressure  closing of AV
valves
– Isovolumetric contraction phase (all valves
are closed)
– In ejection phase, ventricular pressure
exceeds pressure in large arteries, forcing SL
valves open
– End systolic volume (ESV): volume of blood
remaining in each ventricle after systole

92. © 2013 Pearson Education, Inc.
Phases of the Cardiac Cycle
• 3. Isovolumetric relaxation - early
diastole
– Ventricles relax; atria relaxed and filling
– Backflow of blood in aorta and pulmonary
trunk closes SL valves
• Causes dicrotic notch (brief rise in aortic
pressure as blood rebounds off closed valve)
• Ventricles totally closed chambers
– When atrial pressure exceeds that in
ventricles  AV valves open; cycle begins
again at step 1

93. © 2013 Pearson Education, Inc.
Electrocardiogram
Heart sounds
Left heart
QRS
P T P
1st 2nd
Dicrotic notch
120
Aorta
Left ventricle
Left atriumAtrial systole
80
40
0
Pressure(mmHg)
EDV
SV
ESV
120
50
Ventricular
volume(ml)
Atrioventricular valves
Aortic and pulmonary valves
Phase
Open Closed Open
Closed Open Closed
1 2a 2b 3 1
Left atrium
Right atrium
Left ventricle
Right ventricle
Ventricular
filling
Atrial
contraction
Isovolumetric
contraction phase
Ventricular
ejection phase
Isovolumetric
relaxation
Ventricular
filling
Ventricular filling
(mid-to-late diastole)
Ventricular systole
(atria in diastole)
Early diastole
1 2a 2b 3
Figure 18.21 Summary of events during the cardiac cycle.

94. © 2013 Pearson Education, Inc.
Homeostatic Imbalances
• Tachycardia - abnormally fast heart rate
(>100 beats/min)
– If persistent, may lead to fibrillation
• Bradycardia - heart rate slower than
60 beats/min
– May result in grossly inadequate blood
circulation in nonathletes
– May be desirable result of endurance training

95. © 2013 Pearson Education, Inc.
Homeostatic Imbalance
• Congestive heart failure (CHF)
– Progressive condition; CO is so low that blood
circulation inadequate to meet tissue needs
– Reflects weakened myocardium caused by
• Coronary atherosclerosis—clogged arteries
• Persistent high blood pressure
• Multiple myocardial infarcts
• Dilated cardiomyopathy (DCM)

96. © 2013 Pearson Education, Inc.
Homeostatic Imbalance
• Pulmonary congestion
– Left side fails  blood backs up in lungs
• Peripheral congestion
– Right side fails  blood pools in body organs
 edema
• Failure of either side ultimately weakens
other
• Treat by removing fluid, reducing
afterload, increasing contractility

97. © 2013 Pearson Education, Inc.
Developmental Aspects of the Heart
• Embryonic heart chambers
– Sinus venosus
– Atrium
– Ventricle
– Bulbus cordis

98. © 2013 Pearson Education, Inc.
Figure 18.24 Development of the human heart.
Day 20:
Endothelial
tubes begin
to fuse.
4a
4
3
2
1
Tubular
heart
Day 22:
Heart starts
pumping.
Arterial end
Ventricle
Ventricle
Venous end
Day 24: Heart
continues to
elongate and
starts to bend.
Arterial end
Atrium
Venous end
Day 28: Bending
continues as ventricle
moves caudally and
atrium moves cranially.
Aorta
Superior
vena cava
Inferior
vena cava
Ductus
arteriosus
Pulmonary
trunk
Foramen
ovale
Ventricle
Day 35: Bending is
complete.

99. © 2013 Pearson Education, Inc.
Developmental Aspects of the Heart
• Fetal heart structures that bypass
pulmonary circulation
– Foramen ovale connects two atria
• Remnant is fossa ovalis in adult
– Ductus arteriosus connects pulmonary trunk
to aorta
• Remnant - ligamentum arteriosum in adult
– Close at or shortly after birth

100. © 2013 Pearson Education, Inc.
Developmental Aspects of the Heart
• Congenital heart defects
– Most common birth defects; treated with
surgery
– Most are one of two types:
• Mixing of oxygen-poor and oxygen-rich blood, e.g.,
septal defects, patent ductus arteriosus
• Narrowed valves or vessels  increased workload
on heart, e.g., coarctation of aorta
– Tetralogy of Fallot
• Both types of disorders present

101. © 2013 Pearson Education, Inc.
Figure 18.25 Three examples of congenital heart defects.
Occurs in
about 1 in every
500 births
Ventricular septal defect.
The superior part of the
inter-ventricular septum fails
to form, allowing blood to mix
between the two ventricles.
More blood is shunted from
left to right because the left
ventricle is stronger.
Narrowed
aorta
Occurs in
about 1 in every
1500 births
Coarctation of the aorta.
A part of the aorta is
narrowed, increasing the
workload of the left ventricle.
Occurs in
about 1 in every
2000 births
Tetralogy of Fallot.
Multiple defects (tetra =
four): (1) Pulmonary trunk
too narrow and pulmonary
valve stenosed, resulting in
(2) hypertrophied right
ventricle; (3) ventricular
septal defect; (4) aorta
opens from both ventricles.

102. © 2013 Pearson Education, Inc.
Age-Related Changes Affecting the Heart
• Sclerosis and thickening of valve flaps
• Decline in cardiac reserve
• Fibrosis of cardiac muscle
• Atherosclerosis