The Heart - Napa Valley College

Transcription

Chapter
20
The Heart
PowerPoint® Lecture Slides
prepared by Jason LaPres
Lone Star College - North Harris
Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Copyright © 2009 Pearson Education, Inc.,
publishing as Pearson Benjamin Cummings
Introduction to Cardiovascular System
 The Pulmonary Circuit
 Carries blood to and from gas exchange surfaces of
lungs
 The Systemic Circuit
 Carries blood to and from the body
 Blood alternates between pulmonary circuit and
systemic circuit
 Three Types of Blood Vessels
 Arteries
 Carry blood away from heart
 Veins
 Carry blood to heart
 Capillaries
 Networks between arteries and veins
 Capillaries
 Also called exchange vessels
 Exchange materials between blood and
tissues
 Materials include dissolved gases, nutrients,
wastes
Figure 20–1 An Overview of the Cardiovascular System.
 Four Chambers of the Heart
 Right atrium
 Collects blood from systemic circuit
 Right ventricle
 Pumps blood to pulmonary circuit
 Left atrium
 Collects blood from pulmonary circuit
 Left ventricle
 Pumps blood to systemic circuit
Anatomy of the Heart
 Great veins and arteries at the base
 Pointed tip is apex
 Surrounded by pericardial sac
 Sits between two pleural cavities in the
mediastinum
Figure 20–2c
Figure 20–2a The Location of the Heart in the Thoracic Cavity
 The Pericardium
 Double lining of the pericardial cavity
 Parietal pericardium
 Outer layer
 Forms inner layer of pericardial sac
 Visceral pericardium
 Inner layer of pericardium
Figure 20–2c
 The Pericardium
 Pericardial cavity
 Is between parietal and visceral layers
 Contains pericardial fluid
 Pericardial sac
 Fibrous tissue
 Surrounds and stabilizes heart
Figure 20–2b The Location of the Heart in the Thoracic Cavity
Figure 20–c2 The Location of the Heart in the Thoracic Cavity
 Superficial Anatomy of the Heart
 Atria
 Thin-walled
 Expandable outer auricle (atrial appendage)
 Sulci
 Coronary sulcus: divides atria and ventricles
 Anterior interventricular sulcus and posterior
interventricular sulcus:
– separate left and right ventricles
– contain blood vessels of cardiac muscle
Figure 20–3a The Superficial Anatomy of the Heart
Figure 20–3a The Superficial Anatomy of the Heart
Figure 20–3b The Superficial Anatomy of the Heart
Figure 20–3c The Superficial Anatomy of the Heart
 The Heart Wall
 Epicardium (outer layer)
 Visceral pericardium
 Covers the heart
 Myocardium (middle layer)
 Muscular wall of the heart
 Concentric layers of cardiac muscle tissue
 Atrial myocardium wraps around great vessels
 Two divisions of ventricular myocardium
 Endocardium (inner layer)
 Simple squamous epithelium
Figure 20–4 The Heart Wall
 Cardiac Muscle Tissue
 Intercalated discs
 Interconnect cardiac muscle cells
 Secured by desmosomes
 Linked by gap junctions
 Convey force of contraction
 Propagate action potentials
Figure 20–5 Cardiac Muscle Cells
 Characteristics of Cardiac Muscle Cells
 Small size
 Single, central nucleus
 Branching interconnections between cells
 Intercalated discs
 Internal Anatomy and Organization
 Interatrial septum: separates atria
 Interventricular septum: separates ventricles
 Atrioventricular (AV) valves
 Connect right atrium to right ventricle and left atrium to left
ventricle
 The fibrous flaps that form bicuspid (2) and tricuspid (3)
valves
 Permit blood flow in one direction: atria to ventricles
The Heart: Valves
 The Right Atrium
 Superior vena cava
 Receives blood from head, neck, upper limbs, and chest
 Inferior vena cava
 Receives blood from trunk, viscera, and lower limbs
 Coronary sinus
 Cardiac veins return blood to coronary sinus
 Coronary sinus opens into right atrium
 Foramen ovale
 Before birth, is an opening through interatrial
septum
 Connects the two atria
 Seals off at birth, forming fossa ovalis
 Pectinate muscles
 Contain prominent muscular ridges
 On anterior atrial wall and inner surfaces of right
auricle
Figure 20–6a-b The Sectional Anatomy of the Heart.
Figure 20–6a-b The Sectional Anatomy of the Heart.
 The Right Ventricle
 Free edges attach to chordae tendineae
from papillary muscles of ventricle
 Prevent valve from opening backward
 Right atrioventricular (AV) Valve
 Also called tricuspid valve
 Opening from right atrium to right ventricle
 Has three cusps
 Prevents backflow
 The Right Ventricle
 Trabeculae carneae
 Muscular ridges on internal surface of right (and
left) ventricle
 Includes moderator band:
– ridge contains part of conducting system
– coordinates contractions of cardiac muscle cells
 The Pulmonary Circuit
 Conus arteriosus (superior end of 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 three semilunar cusps
 The Left Atrium
 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
 A two-cusped bicuspid valve or mitral valve
 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
Figure 20–6c The Sectional Anatomy of the Heart.
 Structural Differences between the Left
and Right Ventricles
 Right ventricle wall is thinner, develops less
pressure than left ventricle
 Right ventricle is pouch-shaped, left ventricle
is round
Figure 20–7 Structural Differences between the Left and Right
Ventricles
Figure 20–7 Structural Differences between the Left and Right
Ventricles
 The Heart Valves
 Two pairs of one-way valves prevent backflow
during contraction
 Atrioventricular (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
Figure 20–8
 The Heart Valves
 Semilunar valves
 Pulmonary and aortic tricuspid valves
 Prevent backflow from pulmonary trunk and aorta
into ventricles
 Have no muscular support
 Three cusps support like tripod
Figure 20–8
 Aortic Sinuses
 At base of ascending aorta
 Sacs that prevent valve cusps from sticking to
aorta
 Origin of right and left coronary arteries
Figure 20–8a Valves of the Heart
Figure 20–8b Valves of the Heart
Figure 20–8c Valves of the Heart
 Connective Tissues and the Cardiac
(Fibrous) Skeleton
 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
 The Cardiac (Fibrous) Skeleton
 Four bands around heart valves and bases of
pulmonary trunk and aorta
 Stabilize valves
 Electrically insulate ventricular cells from atrial
cells
 The Blood Supply to the Heart = Coronary
Circulation
 Coronary arteries and cardiac veins
 Supplies blood to muscle tissue of heart
 The Coronary Arteries
 Left and right
 Originate at aortic sinuses
 High blood pressure, elastic rebound forces
blood through coronary arteries between
contractions
 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
 Left Coronary Artery
 Supplies blood to
 Left ventricle
 Left atrium
 Interventricular septum
 Two main branches of left coronary artery
 Circumflex artery
 Anterior interventricular artery
 Arterial Anastomoses
 Interconnect anterior and posterior interventricular
arteries
 Stabilize blood supply to cardiac muscle
 The Cardiac Veins
 Great cardiac vein
 Drains blood from area of anterior interventricular artery into
coronary sinus
 Anterior cardiac veins
 Empties into right atrium
 Posterior cardiac vein, middle cardiac vein, and
small cardiac vein
 Empty into great cardiac vein or coronary sinus
Figure 20–9a Coronary Circulation
Figure 20–9b Coronary Circulation
Figure 20–9c Coronary Circulation
Figure 20–10 Coronary Circulation and Clinical Testing
The Conducting System
 Heartbeat
 A single contraction of the heart
 The entire heart contracts in series
 First the atria
 Then the ventricles
 Two Types of Cardiac Muscle Cells
 Conducting system
 Controls and coordinates heartbeat
 Contractile cells
 Produce contractions that propel blood
 The Cardiac Cycle
 Begins with action potential at SA node
 Transmitted through conducting system
 Produces action potentials in cardiac muscle cells (contractile
cells)
 Electrocardiogram (ECG)
 Electrical events in the cardiac cycle can be recorded on an
electrocardiogram (ECG)
Figure 20–11 An Overview of Cardiac Physiology
 A system of specialized cardiac muscle
cells
 Initiates and distributes electrical impulses
that stimulate contraction
 Automaticity
 Cardiac muscle tissue contracts automatically
 Structures of the Conducting System
 Sinoatrial (SA) node - wall of right atrium
 Atrioventricular (AV) node - junction between
atria and ventricles
 Conducting cells - throughout myocardium
 Conducting Cells
 Interconnect SA and AV nodes
 Distribute stimulus through myocardium
 In the atrium
 Internodal pathways
 In the ventricles
 AV bundle and the bundle branches
 Prepotential
 Also called pacemaker potential
 Resting potential of conducting cells
 Gradually depolarizes toward threshold
 SA node depolarizes first, establishing heart
rate
Figure 20–12 The Conducting System of the Heart
 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
 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)
Figure 20–13 Impulse Conduction through the Heart
 The Atrioventricular (AV) Node
 In floor of right atrium
 Receives impulse from SA node (Step 2)
 Delays impulse (Step 3)
 Atrial contraction begins
 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
 Purkinje Fibers
 Distribute impulse through ventricles (Step 5)
 Atrial contraction is completed
 Ventricular contraction begins
 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
 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
 Time Intervals Between ECG Waves
 P–R interval
 From start of atrial depolarization
 To start of QRS complex
 Q–T interval
 From ventricular depolarization
 To ventricular repolarization
Figure 20–14a An Electrocardiogram: Electrode Placement for
Recording a Standard ECG
Figure 20–14b An Electrocardiogram: An ECG Printout
 Contractile Cells
 Purkinje fibers distribute the stimulus to the
contractile cells, which make up most of the
muscle cells in the heart
 Resting Potential
 Of a ventricular cell: about –90 mV
 Of an atrial cell: about –80 mV
Figure 20–15 The Action Potential in Skeletal and Cardiac Muscle
Figure 20–15 The Action Potential in Skeletal and Cardiac Muscle
 Refractory Period
 Absolute refractory period
 Long
 Cardiac muscle cells cannot respond
 Relative refractory period
 Short
 Response depends on degree of stimulus
 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
 The Role of Calcium Ions in Cardiac
Contractions
 Contraction of a cardiac muscle cell is
produced by an increase in calcium ion
concentration around myofibrils
Contractions
 20% of calcium ions required for a contraction
 Calcium ions enter plasma membrane during plateau phase
 Arrival of extracellular Ca2+
 Triggers release of calcium ion reserves from sarcoplasmic
reticulum
Contractions
 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
 The Energy for Cardiac Contractions
 Aerobic energy of heart
 From mitochondrial breakdown of fatty acids and
glucose
 Oxygen from circulating hemoglobin
 Cardiac muscles store oxygen in myoglobin
The Cardiac Cycle
 Cardiac cycle = The period between the
start of one heartbeat and the beginning of
the next
 Includes both contraction and relaxation
The Cardiac Cycle
 Phases of the Cardiac Cycle
 Within any one chamber
 Systole (contraction)
 Diastole (relaxation)
The Cardiac Cycle
Figure 20–16 Phases of the Cardiac Cycle
The Cardiac Cycle
 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
The Cardiac Cycle
 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
The Cardiac Cycle
Eight Steps in the Cardiac Cycle
1. Atrial systole

Atrial contraction begins

Right and left AV valves are open
2. Atria eject blood into ventricles

Filling ventricles
3. Atrial systole ends

AV valves close

Ventricles contain maximum blood volume

Known as end-diastolic volume (EDV)
The Cardiac Cycle
Figure 20–17 Pressure and Volume Relationships in the Cardiac Cycle
The Cardiac Cycle
4. Ventricular systole

Isovolumetric ventricular contraction

Pressure in ventricles rises

AV valves shut
5. Ventricular ejection

Semilunar valves open

Blood flows into pulmonary and aortic trunks

Stroke volume (SV) = 60% of end-diastolic volume
The Cardiac Cycle
The Cardiac Cycle
6. Ventricular pressure falls

Semilunar valves close

Ventricles contain end-systolic volume (ESV), about 40%
of end-diastolic volume
7. Ventricular diastole

Ventricular pressure is higher than atrial pressure

All heart valves are closed

Ventricles relax (isovolumetric relaxation)
The Cardiac Cycle
The Cardiac Cycle
8. Atrial pressure is higher than ventricular
pressure

AV valves open

Passive atrial filling

Passive ventricular filling

Cardiac cycle ends
The Heart: Cardiac Cycle
The Cardiac Cycle
The Cardiac Cycle
 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
The Cardiac Cycle
 Heart Murmur
 Sounds produced by regurgitation through
valves
The Cardiac Cycle
Figure 20–18 Heart Sounds
Cardiodynamics
 The movement and force generated by cardiac
contractions
 End-diastolic volume (EDV)
 End-systolic volume (ESV)
 Stroke volume (SV)
 SV = EDV – ESV
 Ejection fraction
 The percentage of EDV represented by SV
 Cardiac output (CO)
 The volume pumped by left ventricle in 1 minute
Cardiodynamics
Figure 20–19 A Simple Model of Stroke Volume
Cardiodynamics
 Cardiac Output
 CO = HR X SV
 CO = cardiac output (mL/min)
 HR = heart rate (beats/min)
 SV = stroke volume (mL/beat)
Cardiodynamics
 Factors Affecting Cardiac Output
 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
Cardiodynamics
Figure 20–20 Factors Affecting Cardiac Output
Cardiodynamics
 Factors Affecting the Heart Rate
 Autonomic innervation
 Cardiac plexuses: innervate heart
 Vagus nerves (X): carry parasympathetic preganglionic fibers
to small ganglia in cardiac plexus
 Cardiac centers of medulla oblongata:
– cardioacceleratory center controls sympathetic
neurons (increases heart rate)
– cardioinhibitory center controls parasympathetic
neurons (slows heart rate)
Cardiodynamics
 Autonomic Innervation
 Cardiac reflexes
 Cardiac centers monitor:
– blood pressure (baroreceptors)
– arterial oxygen and carbon dioxide levels
(chemoreceptors)
 Cardiac centers adjust cardiac activity
 Autonomic tone
 Dual innervation maintains resting tone by
releasing ACh and NE
 Fine adjustments meet needs of other systems
Cardiodynamics
Figure 20–21 Autonomic Innervation of the Heart
Cardiodynamics
 Effects on the SA Node
 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
Cardiodynamics
Figure 20–22 Autonomic Regulation of Pacemaker Function
Cardiodynamics
 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
Cardiodynamics
 Hormonal Effects on Heart Rate
 Increase heart rate (by sympathetic
stimulation of SA node)
 Epinephrine (E)
 Norepinephrine (NE)
 Thyroid hormone
Cardiodynamics
 Factors Affecting the Stroke Volume
 The EDV: amount of blood a ventricle contains at the
end of diastole
 Filling time:
– duration of ventricular diastole
 Venous return:
– rate of blood flow during ventricular diastole
Cardiodynamics
 Preload
 The degree of ventricular stretching during
ventricular diastole
 Directly proportional to EDV
 Affects ability of muscle cells to produce
tension
Cardiodynamics
 The EDV 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
Cardiodynamics
 The Frank–Starling Principle
 As EDV increases, stroke volume increases
 Physical Limits
 Ventricular expansion is limited by
 Myocardial connective tissue
 The cardiac (fibrous) skeleton
 The pericardial sac
Cardiodynamics
 End-Systolic Volume (ESV)
 The amount of blood that remains in the
ventricle at the end of ventricular systole is
the ESV
Cardiodynamics
 Three 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
Cardiodynamics
 Contractility
 Is affected by
 Autonomic activity
 Hormones
Cardiodynamics
 Effects of Autonomic Activity on Contractility
 Sympathetic stimulation
 NE released by postganglionic fibers of cardiac nerves
 Epinephrine and NE released by suprarenal (adrenal)
medullae
 Causes ventricles to contract with more force
 Increases ejection fraction and decreases ESV
Cardiodynamics
 Effects of Autonomic Activity on
Contractility
 Parasympathetic activity
 Acetylcholine released by vagus nerves
 Reduces force of cardiac contractions
Cardiodynamics
 Hormones
 Many hormones affect heart contraction
 Pharmaceutical drugs mimic hormone actions
 Stimulate or block beta receptors
 Affect calcium ions (e.g., calcium channel
blockers)
Cardiodynamics
 Afterload
 Is increased by any factor that restricts arterial
blood flow
 As afterload increases, stroke volume
decreases
Cardiodynamics
Figure 20–23 Factors Affecting Stroke Volume
Cardiodynamics
 Heart Rate Control Factors
 Autonomic nervous system
 Sympathetic and parasympathetic
 Circulating hormones
 Venous return and stretch receptors
Cardiodynamics
 Stroke Volume Control Factors
 EDV
 Filling time
 Rate of venous return
 ESV
 Preload
 Contractility
 Afterload
Cardiodynamics
 Cardiac Reserve
 The difference between resting and maximal
cardiac output
Cardiodynamics
 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
Cardiodynamics
Figure 20–24 A Summary of the Factors Affecting Cardiac Output

The Heart - Napa Valley College

Transcription

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