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Chapter 20: The Heart Biol 141 A

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Title: Chapter 20: The Heart Biol 141 A


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
The Heart Anatomy
PLAY
Figure 201
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
  • 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
  • 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
  • collects blood from pulmonary circuit
  • Left ventricle
  • pumps blood to systemic circuit

9
Anatomy of the Heart
  • Located directly behind sternum

Y
PLA
Figure 202a
10
Anatomy of the Heart
  • Great veins and arteries at the base
  • Pointed tip is apex

Figure 202c
11
Relation to Thoracic Cavity
Surrounded by pericardial sac Between 2 pleural
cavities In the mediastinum
Figure 202b
12
The Pericardium
  • Double lining of the pericardial cavity

Figure 202c
13
2 Layers of Pericardium
  • Parietal 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 203
16
The Heart Wall
Figure 204
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 205
19
Characteristics of Cardiac Muscle Cells
  1. Small size
  2. Single, central nucleus
  3. Branching interconnections between cells
  4. 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
3D Panorama of the Heart
PLAY
Figure 206a
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
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 207
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 208
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
  1. Physically support cardiac muscle fibers
  2. Distribute forces of contraction
  3. Add strength and prevent overexpansion of heart
  4. Elastic fibers return heart to original shape
    after contraction

36
Blood Supply to the Heart
  • Coronary circulation

Figure 209
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
  • left ventricle
  • left atrium
  • interventricular septum
  • 2 main branches
  • circumflex artery
  • anterior interventricular artery

40
Cardiac Veins
  • Great 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 2011
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 2012
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 80100 action potentials per
    minute
  • Parasympathetic stimulation slows heart rate
  • AV node generates 4060 action potentials per
    minute

49
Impulse Conduction through the Heart
Figure 2013
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 2014b
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
  • PR interval
  • from start of atrial depolarization
  • to start of QRS complex
  • QT 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 2015
60
Resting Potential
  • Of a ventricular 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
  • 250300 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
  • 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 2016
71
4 Phases of the Cardiac Cycle
  1. Atrial systole
  2. Atrial diastole
  3. Ventricular systole
  4. 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 2017
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
Heart Sounds
How do heart sounds relate to specific events in
the cardiac cycle?
Figure 2018b
79
4 Heart Sounds
  • S1
  • loud sounds
  • produced by AV valves
  • S2
  • loud sounds
  • 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 2018a
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 2019
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 2020 (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 2021 (Navigator)
87
Autonomic Pacemaker Regulation
Figure 2022
88
Autonomic Pacemaker Regulation
  • Sympathetic and parasympathetic stimulation
  • greatest at SA node (heart rate)
  • Membrane potential of pacemaker cellslower 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?
  • 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 2023 (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 2024
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 300500

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
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