Transcript 9.Cardiac Physiology

Chapter 9
Cardiac Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Circulatory System
• Three basic components
– Heart
• Serves as pump that establishes the pressure gradient
needed for blood to flow to tissues
– Blood vessels
• Passageways through which blood is distributed from
heart to all parts of body and back to heart
– Blood
• Transport medium within which materials being
transported are dissolved or suspended
Chapter 9 Cardiac Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Circulatory System
• Pulmonary circulation
– Closed loop of vessels
carrying blood between
heart and lungs
• Systemic circulation
– Circuit of vessels
carrying blood between
heart and other body
systems
Chapter 9 Cardiac Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Circulatory System
• Anatomy of the heart
– Hollow, muscular organ about the size of a
clenched fist
– Positioned between two bony structures –
sternum and vertebrae
• Position makes it physically possible to manually drive
blood from heart when it is not pumping effectively
(CPR)
Chapter 9 Cardiac Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Circulatory System
• Heart
• Dual pump
– Right and left sides of heart function as two
separate pumps
– Divided into right and left halves and has four
chambers
• Atria
– Upper chambers
– Receive blood returning to heart and transfer it to lower
chambers
• Ventricles
– Lower chambers which pump blood from heart
Chapter 9 Cardiac Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Circulatory System
• Heart
– Arteries
• Carry blood away from ventricles to tissues
– Veins
• Vessels that return blood from tissues to the atria
– Septum
• Continuous muscular partition that prevents mixture of
blood from the two sides of heart
Chapter 9 Cardiac Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Circuit of Blood Flow
• The venae cavae are veins returning blood to
the right atrium. Oxygen has been extracted
from this blood. Carbon dioxide has been added
to it. This blood is pumped from the right
ventricle through the pulmonary artery to the
lungs.
• The lungs add oxygen to this blood received
from the right side of the heart. Carbon dioxide
is removed from this blood. This blood flows
through pulmonary veins to the left atrium of the
heart. This oxygen rich blood is pumped from
the left ventricle through the aorta, a large artery.
Chapter 9 Cardiac Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Blood Flow Through and Pump Action of the Heart
Chapter 9 Cardiac Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Heart Valves
• Atrioventricular (AV) valves
– Right and left AV valves are positioned between
atrium and ventricle on right and left sides
– Prevent backflow of blood from ventricles into
atria during ventricular emptying
– Right AV valve
• Also called tricuspid valve
– Left AV valve
• Also called bicuspid valve or mitral valve
– Chordae tendinae
• Fibrous cords which prevent valves from being everted
• Papillary muscles
Chapter 9 Cardiac Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Heart Valves
• Semilunar valves
– Aortic and pulmonary valves
– Lie at juncture where major arteries leave
ventricles
– Prevented from everting by anatomic structure
and positioning of cusps
• No valves between atria and veins
– Reasons
• Atrial pressures usually are not much higher than
venous pressures
• Sites where venae cavae enter atria are partially
compressed during atrial contraction
Chapter 9 Cardiac Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Heart Valves
Chapter 9 Cardiac Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Heart Wall
• Consists of three distinct layers
– Endothelium
• Thin inner tissue
• Epithelial tissue which lines entire circulatory system
– Myocardium
• Middle layer
• Composed of cardiac muscle
• Constitutes bulk of heart wall
– Epicardium
• Thin external layer which covers the heart
Chapter 9 Cardiac Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Cardiac Muscle Fibers
• Interconnected by intercalated discs and form
functional syncytia
• Within intercalated discs – two kinds of membrane
junctions
– Desmosomes
– Gap junctions
Chapter 9 Cardiac Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
• Heart is enclosed by pericardial sac
• Pericardial sac has two layers
– Tough, fibrous covering
– Secretory lining
• Secretes pericardial fluid
– Provides lubrication to prevent friction between
pericardial layers
• Pericarditis
– Inflammation of pericardial sac
Chapter 9 Cardiac Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Electrical Activity of Heart
• Heart beats rhythmically as result of action
potentials it generates by itself (autorhythmicity)
• Two specialized types of cardiac muscle cells
– Contractile cells
• 99% of cardiac muscle cells
• Do mechanical work of pumping
• Normally do not initiate own action potentials
– Autorhythmic cells
• Do not contract
• Specialized for initiating and conducting action
potentials responsible for contraction of working cells
Chapter 9 Cardiac Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Electrical Activity of Heart
• Locations of noncontractile cells capable of autorhymicity
– Sinoatrial node (SA node)
• Specialized region in right atrial wall near opening of superior
vena cava
• Pacemaker of the heart
– Atrioventricular node (AV node)
• Small bundle of specialized cardiac cells located at base of
right atrium near septum
– Bundle of His (atrioventricular bundle)
• Cells originate at AV node and enters interventricular septum
• Divides to form right and left bundle branches which travel
down septum, curve around tip of ventricular chambers,
travel back toward atria along outer walls
– Purkinje fibers
• Small, terminal fibers that extend from bundle of His and
spread throughout ventricular myocardium
Chapter 9 Cardiac Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Specialized Conduction System of Heart
Chapter 9 Cardiac Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Electrical Activity of Heart
• Cardiac impulse originates at SA node
• Action potential spreads throughout right and left atria
• Impulse passes from atria into ventricles through AV node
(only point of electrical contact between chambers)
• Action potential briefly delayed at AV node (ensures atrial
contraction precedes ventricular contraction to allow complete
ventricular filling)
• Impulse travels rapidly down interventricular septum by
means of bundle of His
• Impulse rapidly disperses throughout myocardium by means
of Purkinje fibers
• Rest of ventricular cells activated by cell-to-cell spread of
impulse through gap junctions
Chapter 9 Cardiac Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Spread of Cardiac Excitation
Chapter 9 Cardiac Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Electrical Activity of Heart
• Atria contract as single unit followed after brief delay
by a synchronized ventricular contraction
• Action potentials of cardiac contractile cells exhibit
prolonged positive phase (plateau) accompanied by
prolonged period of contraction
– Ensures adequate ejection time
– Plateau primarily due to activation of slow L-type
Ca2+ channels
Chapter 9 Cardiac Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Electrical Activity of Heart
• Ca2+ entry through L-type channels in T tubules
triggers larger release of Ca2+ from sarcoplasmic
reticulum
– Ca2+ induced Ca2+ release leads to cross-bridge
cycling and contraction
Chapter 9 Cardiac Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
ExcitationContraction
Coupling in Cardiac
Contractile Cells
Chapter 9 Cardiac Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Electrical Activity of Heart
• Because long refractory period occurs in conjunction
with prolonged plateau phase, summation and
tetanus of cardiac muscle is impossible
– Ensures alternate periods of contraction and
relaxation which are essential for pumping blood
Chapter 9 Cardiac Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Relationship of an Action
Potential and the Refractory
Period to the Duration of the
Contractile Response in
Cardiac Muscle
Chapter 9 Cardiac Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Electrocardiogram (ECG)
• Record of overall spread of electrical activity through heart
• Represents
– Recording part of electrical activity induced in body fluids
by cardiac impulse that reaches body surface
• Not direct recording of actual electrical activity of heart
– Recording of overall spread of activity throughout heart
during depolarization and repolarization
• Not a recording of a single action potential in a single cell at a
single point in time
– Comparisons in voltage detected by electrodes at two
different points on body surface, not the actual potential
• Does not record potential at all when ventricular muscle is
either completely depolarized or completely repolarized
Chapter 9 Cardiac Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Electrocardiogram (ECG)
Different parts of ECG record can be correlated to specific cardiac
events
Chapter 9 Cardiac Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Abnormalities in Rate
• Tachycardia
– Rapid heart rate of more than 100 beats per
minute
• Bradycardia
– Slow heart rate of fewer than 60 beats per minute
Chapter 9 Cardiac Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Abnormalities in Rhythm
• Rhythm
– Regularity or spacing of ECG waves
• Arrhythmia
– Variation from normal rhythm and sequence of
excitation of the heart
– Examples
•
•
•
•
Atrial flutter
Atrial fibrillation
Ventricular fibrillation
Heart block
Chapter 9 Cardiac Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Cardiac Myopathies
• Damage of the heart muscle
– Myocardial ischemia
• Inadequate delivery of oxygenated blood to heart tissue
– Necrosis
• Death of heart muscle cells
– Acute myocardial infarction (heart attack)
• Occurs when blood vessel supplying area of heart
becomes blocked or ruptured
Chapter 9 Cardiac Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Representative Heart Conditions Detectable Through ECG
Chapter 9 Cardiac Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Cardiac Output
• Volume of blood ejected by each ventricle each
minute
• Determined by
heart rate times
stroke volume
Chapter 9 Cardiac Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Cardiac Output
• Heart rate is varied by altering balance of
parasympathetic and sympathetic influence on SA
node
– Parasympathetic stimulation slows heart rate
– Sympathetic stimulation speeds it up
Chapter 9 Cardiac Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Cardiac Output
• Stroke volume
– Determined by extent of venous return and by
sympathetic activity
– Influenced by two types of controls
• Intrinsic control
• Extrinsic control
– Both factors increase stroke volume by increasing
strength of heart contraction
Chapter 9 Cardiac Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Frank-Starling Law of the Heart
• States that heart normally pumps out during systole
the volume of blood returned to it during diastole
Chapter 9 Cardiac Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Nourishing the Heart Muscle
• Muscle is supplied with oxygen and nutrients by
blood delivered to it by coronary circulation, not from
blood within heart chambers
• Heart receives most of its own blood supply that
occurs during diastole
– During systole, coronary vessels are compressed
by contracting heart muscle
• Coronary blood flow normally varies to keep pace
with cardiac oxygen needs
Chapter 9 Cardiac Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Coronary Artery Disease (CAD)
• Pathological changes within coronary artery walls
that diminish blood flow through the vessels
• Leading cause of death in United States
• Can cause myocardial ischemia and possibly lead to
acute myocardial infarction
– Three mechanisms
• Profound vascular spasm of coronary arteries
• Formation of atherosclerotic plaques
• Thromboembolism
Chapter 9 Cardiac Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Possible Outcomes of Acute Myocardial Infarction (Heart Attack)
Chapter 9 Cardiac Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Cardiac Anatomy
Cardiac Cycle
Conduction