1. Chapter 20: The Heart Biol 141 A& P R.L. Brashear-Kaulfers

2. How are the cardiovascular system and heart organized?

3. Organization of the Cardiovascular System
PLAY
The Heart: Anatomy
Figure 20–1

4. The Pulmonary Circuit
Carries blood to and from gas exchange surfaces of lungs
The Systemic Circuit
Carries blood to and from the body
Alternating Circuits
Blood alternates between pulmonary circuit and systemic circuit

5. 3 Types of Blood Vessels Arteries: Veins: Capillaries:
carry blood away from heart
Veins:
carry blood to heart
Capillaries:
networks between arteries and veins

6. Capillaries Also called exchange vessels
Exchange materials between blood and tissues
Dissolved gases, nutrients, wastes

7. 4 Chambers of the Heart 2 for each circuit: Right atrium:
left and right: ventricles and atria
Right atrium:
collects blood from systemic circuit
Right ventricle:
pumps blood to pulmonary circuit

8. 4 Chambers of the Heart Left atrium: Left ventricle:
collects blood from pulmonary circuit
Left ventricle:
pumps blood to systemic circuit

9. Anatomy of the Heart Located directly behind sternum PLA Y
Figure 20–2a

10. Anatomy of the Heart Great veins and arteries at the base
Pointed tip is apex
Figure 20–2c

11. Relation to Thoracic Cavity
Surrounded by pericardial sac
Between 2 pleural cavities
In the mediastinum
Figure 20–2b

12. The Pericardium
Double lining of the pericardial cavity
Figure 20–2c

13. 2 Layers of Pericardium Parietal pericardium: Visceral pericardium:
outer layer
forms inner layer of pericardial sac
Visceral pericardium:
inner layer of pericardium

14. Structures of Pericardium
Pericardial cavity:
Is between parietal and visceral layers
contains pericardial fluid
Pericardial sac:
fibrous tissue
surrounds and stabilizes heart
Pericarditis
An infection of the pericardium

15. Superficial Anatomy of the Heart
4 cardiac chambers
Atria - Thin-walled
Expandable outer auricle
Coronary sulcus:
divides atria and ventricles
Anterior and posterior interventricular sulci:
separate left and right ventricles
contain blood vessels of cardiac muscle
Figure 20–3

16. The Heart Wall
Figure 20–4

17. 3 Layers of the Heart Wall
Epicardium:- outer layer
Visceral pericardium , Covers the heart
Myocardium: middle layer, Muscular wall
Concentric layers of cardiac muscle tissue
Atrial myocardium wraps around great vessels
2 divisions of ventricular myocardium
Endocardium: inner layer

18. Cardiac Muscle Cells Intercalated discs:
interconnect cardiac muscle cells
secured by desmosomes
linked by gap junctions
convey force of contraction
propagate action potentials
Figure 20–5

19. Characteristics of Cardiac Muscle Cells
Small size
Single, central nucleus
Branching interconnections between cells
Intercalated discs

20. Cardiac Cells vs. Skeletal Fibers
Table 20-1

21. What is the path of blood flow through the heart, and what are the major blood vessels, chambers, and heart valves?

22. Internal Anatomy
PLAY
3D Panorama of the Heart
Figure 20–6a

23. Atrioventricular (AV) Valves
Connect right atrium to right ventricle and left atrium to left ventricle
Permit blood flow in 1 direction:
atria to ventricles
Septa –
Interatrial septum:
separates atria
Interventricular septum:
separates ventricles

24. The Vena Cava Delivers systemic circulation to right atrium
Superior vena cava:
receives blood from head, neck, upper limbs, and chest
Inferior vena cava:
receives blood from trunk, and viscera, lower limbs
Coronary Sinus
Cardiac veins return blood to coronary sinus
Coronary sinus opens into right atrium

25. Foramen Ovale Before birth, is an opening through interatrial septum
Connects the 2 atria
Seals off at birth, forming fossa ovalis

26. Right Atrioventricular (AV) Valve
Cusps - Fibrous flaps that form bicuspid (2) and tricuspid (3) valves- Prevent valve from opening backward
Right Atrioventricular (AV) Valve
Also called tricuspid valve
Opening from right atrium to right ventricle
Has 3 cusps
Prevents backflow

27. The Pulmonary Circuit
Conus arteriosus (superior right ventricle) leads to pulmonary trunk
Pulmonary trunk divides into left and right pulmonary arteries
Blood flows from right ventricle to pulmonary trunk through pulmonary valve
Pulmonary valve has 3 semilunar cusps

28. Return from Pulmonary Circuit
Blood gathers into left and right pulmonary veins
Pulmonary veins deliver to left atrium
Blood from left atrium passes to left ventricle through left atrioventricular (AV) valve
2-cusp bicuspid valve or mitral valve

29. The Left Ventricle Holds same volume as right ventricle
Is larger; muscle is thicker, and more powerful
Similar internally to right ventricle, but does not have moderator band
Systemic circulation:
blood leaves left ventricle through aortic valve into ascending aorta
ascending aorta turns (aortic arch) and becomes descending aorta

30. Left and Right Ventricles
Have significant structural differences
Right ventricle wall is thinner, develops less pressure than left ventricle
Right ventricle is pouch-shaped, left ventricle is round
Figure 20–7

31. The Heart Valves One-way valves prevent backflow during contraction
(AV) Valves- between atria and ventricles
Blood pressure closes valve cusps during ventricular contraction
Papillary muscles tense chordae tendineae:
prevent valves from swinging into atria
Regurgitation -Failure of valves
Causes backflow of blood into atria
Figure 20–8

32. Semilunar Valves Pulmonary and aortic tricuspid valves
Prevent backflow from pulmonary trunk and aorta into ventricles
Have no muscular support
3 cusps support like tripod

33. Aortic Sinuses - at base of ascending aorta
Prevent valve cusps from sticking to aorta
Origin of right and left coronary arteries
Carditis - An inflammation of the heart
Can result in valvular heart disease (VHD): e.g., rheumatic fever

34. KEY CONCEPT The heart has 4 chambers:
2 for pulmonary circuit:
right atrium and right ventricle
2 for systemic circuit:
left atrium and left ventricle
Left ventricle has a greater workload
Is much more massive than right ventricle, but the two chambers pump equal amounts of blood
AV valves prevent backflow from ventricles into atria
Semilunar valves prevent backflow from aortic and pulmonary trunks into ventricles

35. Connective Tissue Fibers of the Heart
Physically support cardiac muscle fibers
Distribute forces of contraction
Add strength and prevent overexpansion of heart
Elastic fibers return heart to original shape after contraction

36. Blood Supply to the Heart
Coronary circulation
Figure 20–9

37. Coronary Circulation Coronary arteries-Left and right
Originate at aortic sinuses
High blood pressure, elastic rebound force blood through coronary arteries between contractions
cardiac veins
Supplies blood to muscle tissue of heart

38. Right Coronary Artery Supplies blood to: right atrium
portions of both ventricles
cells of sinoatrial (SA) and atrioventricular nodes
marginal arteries (surface of right ventricle)
posterior interventricular artery

39. Left Coronary Artery Supplies blood to: 2 main branches:
left ventricle
left atrium
interventricular septum
2 main branches:
circumflex artery
anterior interventricular artery

40. Cardiac Veins Great cardiac vein: Anterior cardiac vein:
drains blood from area of anterior interventricular artery into coronary sinus
Anterior cardiac vein:
empties into right atrium
Posterior cardiac vein, middle cardiac vein, and small cardiac vein:
empty into great cardiac vein or coronary sinus

41. The Cardiac Cycle The Heartbeat A single contraction of the heart
The entire heart contracts in series:
first the atria
then the ventricles
Figure 20–11

42. 2 Types of Cardiac Muscle Cells
Conducting system:
controls and coordinates heartbeat
Contractile cells:
produce contractions
* The Cardiac Cycle begins with action potential at SA node
transmitted through conducting system
produces action potentials in cardiac muscle cells (contractile cells)
Electrical events in the cardiac cycle can be recorded on an electrocardiogram (ECG)

43. The Conducting System
Figure 20–12

44. The Conducting System A system of specialized cardiac muscle cells:
initiates and distributes electrical impulses that stimulate contraction
Automaticity:
cardiac muscle tissue contracts automatically

45. Structures of the Conducting System
Sinoatrial (SA) node
Atrioventricular (AV) node
Conducting cells

46. Conducting Cells Interconnect SA and AV nodes
Distribute stimulus through myocardium
In the atrium:
internodal pathways
In the ventricles:
AV bundle and bundle branches

47. Prepotential Also called pacemaker potential
Resting potential of conducting cells:
gradually depolarizes toward threshold
SA node depolarizes first, establishing heart rate

48. Heart Rate SA node generates 80–100 action potentials per minute
Parasympathetic stimulation slows heart rate
AV node generates 40–60 action potentials per minute

49. Impulse Conduction through the Heart
Figure 20–13

50. The Sinoatrial (SA) Node
In posterior wall of right atrium
Contains pacemaker cells
Connected to AV node by internodal pathways
Begins atrial activation (Step 1)

51. The Atrioventricular (AV) Node
In floor of right atrium
Receives impulse from SA node (Step 2)
Delays impulse (Step 3)
Atrial contraction begins

52. The AV Bundle In the septum
Carries impulse to left and right bundle branches:
which conduct to Purkinje fibers (Step 4)
And to the moderator band:
which conducts to papillary muscles
4. The Purkinje Fibers
Distribute impulse through ventricles (Step 5)
Atrial contraction is completed
Ventricular contraction begins

53. Abnormal Pacemaker Function
Bradycardia:
abnormally slow heart rate
Tachycardia:
abnormally fast heart rate
Ectopic Pacemaker:
Abnormal cells
Generate high rate of action potentials
Bypass conducting system
Disrupt ventricular contractions

54. The Electrocardiogram
Figure 20–14b

55. Electrocardiogram (ECG or EKG)
A recording of electrical events in the heart
Obtained by electrodes at specific body locations
Abnormal patterns diagnose damage
Features of an ECG :
P wave: atria depolarize
QRS complex: ventricles depolarize
T wave: ventricles repolarize

56. Time Intervals P–R interval: Q–T interval: Cardiac Arrhythmias –
from start of atrial depolarization
to start of QRS complex
Q–T interval:
from ventricular depolarization
to ventricular repolarization
Cardiac Arrhythmias –
Abnormal patterns of cardiac electrical activity

57. KEY CONCEPT Heart rate is normally established by cells of SA node
Rate can be modified by autonomic activity, hormones, and other factors
From the SA node, stimulus is conducted to AV node, AV bundle, bundle branches, and Purkinje fibers before reaching ventricular muscle cells
Electrical events associated with the heartbeat can be monitored in an electrocardiogram (ECG)

58. What events take place during an action potential in cardiac muscle?

59. Action Potentials in Skeletal and Cardiac Muscle
Figure 20–15

60. Resting Potential Of a ventricular cell: Of an atrial cell:
about —90 mV
Of an atrial cell:
about —80 mV

61. 3 Steps of Cardiac Action Potential
Rapid depolarization:
voltage-regulated sodium channels (fast channels) open

62. 3 Steps of Cardiac Action Potential
As sodium channels close:
voltage-regulated calcium channels (slow channels) open
balance Na+ ions pumped out
hold membrane at 0 mV plateau

63. 3 Steps of Cardiac Action Potential
Repolarization:
plateau continues
slow calcium channels close
slow potassium channels open
rapid repolarization restores resting potential

64. The Refractory Periods
Absolute refractory period:
long
cardiac muscle cells cannot respond
Relative refractory period:
short
response depends on degree of stimulus

65. Timing of Refractory Periods
Length of cardiac action potential in ventricular cell:
250–300 msecs
30 times longer than skeletal muscle fiber
long refractory period prevents summation and tetany

66. Contraction of a cardiac muscle cell is produced by an increase in calcium ion concentration around myofibrils
20% of calcium ions required for a contraction:
calcium ions enter cell membrane during plateau phase
Arrival of extracellular Ca2+:
triggers release of calcium ion reserves from sarcoplasmic reticulum

67. Intracellular and Extracellular Calcium
As slow calcium channels close:
intracellular Ca2+ is absorbed by the SR
or pumped out of cell
Cardiac muscle tissue:
very sensitive to extracellular Ca2+ concentrations

68. The Cardiac Cycle
The period between the start of 1 heartbeat and the beginning of the next
Includes both contraction and relaxation
2 Phases of the Cardiac Cycle:
Within any 1 chamber:
systole (contraction)
diastole (relaxation)

69. Blood Pressure In any chamber: Blood flows from high to low pressure:
rises during systole
falls during diastole
Blood flows from high to low pressure:
controlled by timing of contractions
directed by one-way valves

70. Phases of the Cardiac Cycle
Figure 20–16

71. 4 Phases of the Cardiac Cycle
Atrial systole
Atrial diastole
Ventricular systole
Ventricular diastole

72. Cardiac Cycle and Heart Rate
At 75 beats per minute:
cardiac cycle lasts about 800 msecs
When heart rate increases:
all phases of cardiac cycle shorten, particularly diastole

73. Pressure and Volume in the Cardiac Cycle
8 steps in the cardiac cycle
Figure 20–17

74. 8 Steps in the Cardiac Cycle
Atrial systole:
atrial contraction begins
right and left AV valves are open
Atria eject blood into ventricles:
filling ventricles
Atrial systole ends:
AV valves close
ventricles contain maximum volume
end-diastolic volume (EDV)
Ventricular systole:
isovolemic ventricular contraction
pressure in ventricles rises
AV valves shut

75. 8 Steps in the Cardiac Cycle
Ventricular ejection:
semilunar valves open
blood flows into pulmonary and aortic trunks
Stroke volume (SV) = 60% of end-diastolic volume
Ventricular pressure falls:
semilunar valves close
ventricles contain end-systolic volume (ESV), about 40% of end-diastolic volume

76. 8 Steps in the Cardiac Cycle
Ventricular diastole:
ventricular pressure is higher than atrial pressure
all heart valves are closed
ventricles relax (isovolumetric relaxation)
Atrial pressure is higher than ventricular pressure:
AV valves open
passive atrial filling
passive ventricular filling
cardiac cycle ends

77. Heart Failure
Lack of adequate blood flow to peripheral tissues and organs due to ventricular damage

78. How do heart sounds relate to specific events in the cardiac cycle?
Figure 20–18b

79. 4 Heart Sounds S1: S2: S3, S4: loud sounds produced by AV valves
produced by semilunar valves
S3, S4:
soft sounds
blood flow into ventricles and atrial contraction

80. Positioning the Stethoscope
To detect sounds of each valve
Heart Murmur-
Sounds produced by regurgitation through valves
Figure 20–18a

81. Aerobic Energy of Heart
From mitochondrial breakdown of fatty acids and glucose
Oxygen from circulating hemoglobin
Cardiac muscles store oxygen in myoglobin

82. Stroke Volume
Volume (ml) of blood ejected per beat
Figure 20–19

83. Cardiac Output Cardiac output (CO) ml/min =
Heart rate (HR) beats/min 
Stroke volume (SV) ml/beat

84. Overview: Control of Cardiac Output
Figure 20–20 (Navigator)

85. Adjusting to Conditions
Cardiac output:
adjusted by changes in heart rate or stroke volume
Heart rate:
adjusted by autonomic nervous system or hormones
Stroke volume:
adjusted by changing EDV or ESV

86. What variables influence heart rate? Autonomic Innervation
Figure 20–21 (Navigator)

87. Autonomic Pacemaker Regulation
Figure 20–22

88. Autonomic Pacemaker Regulation
Sympathetic and parasympathetic stimulation:
greatest at SA node (heart rate)
Membrane potential of pacemaker cells:lower than other cardiac cells
Rate of spontaneous depolarization depends on:
resting membrane potential
rate of depolarization
ACh (parasympathetic stimulation):
slows the heart
NE (sympathetic stimulation):
speeds the heart

89. Atrial Reflex Also called Bainbridge reflex
Adjusts heart rate in response to venous return
Stretch receptors in right atrium:
trigger increase in heart rate
through increased sympathetic activity

90. Hormonal Effects on Heart Rate
Increase heart rate (by sympathetic stimulation of SA node):
epinephrine (E)
norepinephrine (NE)
thyroid hormone

91. Factors Affecting Stroke Volume
What variables influence stroke volume?
Factors Affecting Stroke Volume
Changes in EDV or ESV
2 Factors Affect EDV-
1. Filling time:
duration of ventricular diastole
2. Venous return:
rate of blood flow during ventricular diastole
Figure 20–23 (Navigator)

92. Preload
The degree of ventricular stretching during ventricular diastole
Directly proportional to EDV
Affects ability of muscle cells to produce tension

93. EDV, Preload, and Stroke Volume
At rest:
EDV is low
myocardium stretches less
stroke volume is low
With exercise:
EDV increases
myocardium stretches more
stroke volume increases
As EDV increases, stroke volume increases

94. Physical Limits Ventricular expansion is limited by:
myocardial connective tissue
the fibrous skeleton
the pericardial sac
End-Systolic Volume (ESV)
The amount of blood that remains in the ventricle at the end of ventricular systole is the ESV

95. 3 Factors that Affect ESV
Preload:
ventricular stretching during diastole
Contractility:
force produced during contraction, at a given preload
Afterload:
tension the ventricle produces to open the semilunar valve and eject blood

96. Contractility is affected by: autonomic activity & hormones :
Sympathetic stimulation:
NE released by postganglionic fibers of cardiac nerves
epinephrine and NE released by adrenal medullae
causes ventricles to contract with more force
increases ejection fraction and decreases ESV
Parasympathetic activity:
acetylcholine released by vagus nerves
reduces force of cardiac contractions

97. Hormones and Contractility
Many hormones affect heart contraction
Pharmaceutical drugs mimic hormone actions:
stimulate or block beta receptors
affect calcium ions e.g., calcium channel blockers

98. Afterload
Is increased by any factor that restricts arterial blood flow
As afterload increases, stroke volume decreases

99. Factors Affecting Heart Rate and Stroke Volume
Autonomic nervous system:
sympathetic and parasympathetic
Circulating hormones
Venous return and stretch receptors
Figure 20–24

100. Stroke Volume Control Factors
EDV:
filling time
rate of venous return
ESV:
preload
contractility
Afterload
Cardiac Reserve-
The difference between resting and maximal cardiac output

101. KEY CONCEPT Cardiac output:
the amount of blood pumped by the left ventricle each minute
adjusted by the ANS in response to:
circulating hormones
changes in blood volume
alterations in venous return
Most healthy people can increase cardiac output by 300–500%

102. The Heart and Cardiovascular System
Cardiovascular regulation:
ensures adequate circulation to body tissues
Cardiovascular centers:
control heart and peripheral blood vessels
Cardiovascular system responds to:
changing activity patterns
circulatory emergencies

103. SUMMARY (1) Organization of cardiovascular system:
pulmonary and systemic circuits
3 types of blood vessels:
arteries, veins, and capillaries
4 chambers of the heart:
left and right atria
left and right ventricles
Pericardium, mediastinum, and pericardial sac
Coronary sulcus and superficial anatomy of the heart
Structures and cells of the heart wall

104. SUMMARY (2) Internal anatomy and structures of the heart:
septa, muscles, and blood vessels
Valves of the heart and direction of blood flow
Connective tissues of the heart
Coronary blood supply
Contractile cells and the conducting system:
pacemaker calls, nodes, bundles, and Purkinje fibers

105. SUMMARY (3) Electrocardiogram and its wave forms
Refractory period of cardiac cells
Cardiac cycle:
atrial and ventricular
systole and diastole
Cardiodynamics:
stroke volume and cardiac output
Control of cardiac output