Functional Human Physiology for the Exercise and Sport Sciences The Cardiovascular System: Cardiac Function

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Functional Human Physiologyfor the Exercise and
Sport Sciences The Cardiovascular System
Cardiac Function

• Jennifer L. Doherty, MS, ATC
• Department of Health, Physical Education, and
  Recreation
• Florida International University

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Overview of the Cardiovascular System

• 3 components
• The Heart
• Blood Vessels
• Blood

• The Heart
• Atria
• Ventricles
• Interatrial Septum
• Interventricular Septum
• Atrioventricular valves
• Semilunar valves

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Overview of the Cardiovascular System

• Blood Vessels
• Arteries
• Arterioles
• Capillaries
• Venules
• Veins

• Blood
• Erythrocytes
• Leukocytes
• Platelets
• Plasma

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The Path of Blood Flow Through the Heart and
Vasculature

• Pulmonary Circuit
• Blood flow between the lungs and heart
• Supplied by the Right side of the heart

• Systemic Circuit
• Blood flow between the rest of the body and heart
• Supplied by the Left side of the heart

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The Path of Blood Flow Through the Heart and
Vasculature

• Right Atrium
• Receives deoxygenated blood from the body
• Blood passes through the Right AV (tricuspid)
  valve
• Enters the Right Ventricle
• Right Ventricle
• Pumps blood into the Pulmonary Circuit
• Blood passes through the Pulmonary Semilunar
  valve
• Enters the Pulmonary Trunk ? Pulmonary arteries ?
  Lungs

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The Path of Blood Flow Through the Heart and
Vasculature

• Left Atrium
• Receives oxygenated blood from the Lungs
• Blood passes through the Left AV (bicuspid) valve
  
• Enters the Left Ventricle
• Left Ventricle
• Pumps blood into the systemic circuit
• Blood passes through the Aortic Semilunar valve
• Enters the Aorta ? Arteries ? Arterioles ?
  Capillaries ? Venules ? Veins

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The Conduction System of the Heart

• Autorhythmicity
• Ability of the heart to generate electrical
  signals that trigger cardiac muscle contractions
  in a periodic manner
• Autorhythmic cells (2 types)
• Coordinate and provide a rhythmic heartbeat
• Repeatedly and spontaneously depolarize neurons
• Do not rely on external nervous stimulation
• Pacemaker Cells
• Initiate action potentials, which establish the
  heart rhythm
• Conduction Fibers
• Transmit action potentials throughout the heart

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The Conduction System of the Heart

• Conduction pathways
• Depolarization spreads throughout the heart very
  rapidly facilitating a coordinated contraction
  pattern
• Intercalated disks
• Form junctions between adjacent cardiac muscle
  fibers
• Contain a high concentration of gap junctions for
  rapid transmission of the action potential

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Initiation and Conduction of an Impulse During a
Heartbeat

• Action Potential is initiated at the Sinoatrial
  (SA) Node
• Sinoatrial (SA) Node
• Small cluster of cells in the right atrial wall,
  just inferior to the entrance of the superior
  vena cava
• Fastest spontaneous depolarization rate
• Approximately 70 - 80 bpm (normal resting
  heartbeat)
• Establishes the normal pacemaker of the heart
• Called Sinus rhythm

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Initiation and Conduction of an Impulse During a
Heartbeat

• Action Potential travels from the SA Node toward
  the AV Node
• Travel along Internodal pathways
• System of conduction fibers that run along the
  walls of the atria to the AV Node
• Travel along Interartrial pathways
• System of conduction fibers that run along the
  walls of the atria to the cardiac muscle

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Initiation and Conduction of an Impulse During a
Heartbeat

• The impulse is conducted to the cells of the AV
  Node
• Atrioventricular (AV) Node
• Located in the interatrial septum just above the
  tricuspid valve.
• Spontaneously depolarizes
• AV delay
• Slight delay in conduction due to the smaller
  diameter of these conduction fibers
• Allows the atria to finish contracting before the
  ventricles depolarize and contraction

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Initiation and Conduction of an Impulse During a
Heartbeat

• Impulse travels from the AV Node through the
  Atrioventricular (AV) Bundle
• Compact bundle of muscle fibers
• Located in the interventricular septum
• Also called the Bundle of His
• After the slight AV delay, the action potential
  passes rapidly through the AV bundle since it has
  large fibers
• The depolarization then passes to the bundle
  branches

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Initiation and Conduction of an Impulse During a
Heartbeat

• The impulse travels to the Right and Left Bundle
  Branches
• Located in the interventricular septum
• Conduct the impulse to the right and left
  ventricles
• They pass the depolarization impulse rapidly to
  the Purkinje fibers.

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Initiation and Conduction of an Impulse During a
Heartbeat

• The impulse travels from the Bundles Branches to
  the Purkinje Fibers
• Purkinje Fibers
• Large diameter, rapid conduction fibers
• Spread the impulse to the ventricular myocardium
• Responsible for approximately simultaneous
  excitation of the ventricles which is essential
  for efficient pumping
• Total time elapsed between excitation of SA node
  and ventricular depolarization is about 0.22 sec

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Electrical Activity in the Heart

• Cardiac Contractile Cells
• Resting membrane potential in cardiac cells is
  approximately -90 mV
• Cardiac action potentials
• Depolarization causes the opening of Ca
  voltage-gated channels
• Affects membrane potential
• Triggers cardiac muscle contraction
• Special K voltage-gated channels close in
  response to depolarization
• Reduces membrane permeability to potassium

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Spread of Action Potentials through the heart
Phases of the Action Potential

• Phase 0 Depolarization
• Causes Na voltage-gated channels to open
• Increases permeability to Na
• Na ions follow their electrochemical gradient
  into the cell
• Membrane potential becomes more positive

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Spread of Action Potentials through the heart
Phases of the Action Potential

• Phase 1 Repolarization
• Na voltage-gated channel inactivation gates
  close
• Decreases permeability to Na
• K voltage-gated channels close (in response to
  depolarization)
• Decreases the flow of K out of the cell
• Ca voltage-gated channels open
• Increases permeability to Ca
• Ca flows into the cell

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Spread of Action Potentials through the heart
Phases of the Action Potential

• Phase 2 Plateau
• K channels stay closed
• Ca channels stay open
• Ca influx prolongs depolarization
• Membrane remains depolarized
• The purpose of the plateau phase is to prevent
  tetany (prolonged contractions) that would
  interfere with the pumping ability of the heart

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Spread of Action Potentials through the heart
Phases of the Action Potential

• Phase 3 Repolarization
• K voltage-gated channels open
• Increases permeability to K
• K flows out of cell
• Results in repolarization
• Ca channels begin to close
• Ca is pumped back into the SR
• Ca is pumped out of cell into the extracellular
  fluid

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Spread of Action Potentials through the heart
Phases of the Action Potential

• Phase 4 Resting
• Resting potential is re-established at -90 mV

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Excitation-Contraction Coupling in Cardiac Muscle
Fibers

• Action potential spreads along the cell membrane
  and down T-tubules
• Causes Ca voltage-gated channels to open
• SR Ca voltage-gated channels release Ca into
  the cytosol
• Membrane Ca voltage-gated channels allow Ca
  from extracellular fluid to enter cell

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Excitation-Contraction Coupling in Cardiac Muscle
Fibers

• Cardiac muscle has less extensive SRs compared to
  skeletal muscle
• Therefore, cardiac muscle contraction depends
  heavily on Ca influx from the extracellular
  fluid
• When depolarization occurs, Ca voltage-gated
  channels open
• Allows influx of Ca from the extracellular
  fluid
• The strength of cardiac muscle contraction is
  directly related to the amount of Ca that
  enters the cell from the extracellular fluid
• Unlike skeletal muscle cells because it is able
  to store large amounts of Ca in the SR

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Excitation-Contraction Coupling in Cardiac Muscle
Fibers

• In cardiac muscle, the SR releases more Ca with
  each action potential
• Called Calcium-induced calcium release
• Ca binds to troponin shifting tropomyosin off
  of the myosin-binding sites on actin
• Cross-bridge cycling occurs
• The all-or-none law applies to the entire
  functional syncytium in cardiac muscle, not to
  individual muscle fibers as in skeletal muscle

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Excitation-Contraction Coupling in Cardiac Muscle
Fibers

• For cardiac muscle to relax, Ca must be removed
  from the cytosol
• Ca is removed from troponin and tropomyosin
  shifts back over the myosin-binding sites on
  action
• The muscle fiber then relaxes

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Recording the Electrical Activity of the Heart
with Electrocardiograms

• Electrocardiogram (ECG or EKG)
• A recording of the electrical changes that occur
  in the myocardium during the cardiac cycle
• A graphic representation of the electrical
  activity of the heart obtained by electrodes on
  the surface of the skin
• Body fluids conduct the electrical activity that
  can be detected by the electrodes.

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Recording the Electrical Activity of the Heart
with Electrocardiograms

• Einthovens triangle
• Imaginary triangle formed by the leads of the EKG
• Each lead has a () and (-) electrode
• Detects the difference in surface electrical
  potential between the positive and negative
  electrodes

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Waveforms of a Normal EKG

• P wave
• P-R interval
• QRS complex
• T wave

• Only electrical events of the heart, such as
  arrhythmias or conduction blocks, can be detected
  on an EKG
• No information about the mechanical events of the
  heart are revealed by the EKG

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Waveforms of a Normal EKG

• P wave
• Marks depolarization of the atria
• Includes the time in which the SA node sends the
  electrical impulse toward the AV node
• This depolarization spreads as a wave of impulses
  across both atria, causing them to contract

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Waveforms of a Normal EKG

• P-R interval
• Includes the time required for the electrical
  impulse to spread from the atria, through the AV
  node, to the ventricles

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Waveforms of a Normal EKG

• QRS complex
• Represents depolarization of the ventricles
• Leads to ventricular contraction
• The wave is large because the ventricles have
  thicker walls and therefore produce a greater
  electrical impulse

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Waveforms of a Normal EKG

• T wave
• Occurs as the ventricles slowly repolarize

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Waveforms of a Normal EKG

• Repolarization of the atria
• Occurs during ventricular depolarization and is
  obscured by the QRS complex

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The Cardiac Cycle

• Includes all events associated with the flow of
  blood through the heart during a single, complete
  heartbeat
• During the cardiac cycle, pressure changes occur
  as the atria and ventricles alternately contract
  and relax
• When a chamber of the heart contracts, there is
  an increase in blood pressure inside the chamber
• When a chamber of the heart relaxes, there is a
  decrease in blood pressure inside the chamber
• Blood always flows from regions of high pressure
  to low pressure

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The Cardiac Cycle

• Mechanical events of the cardiac cycle are
  associated with changes in pressure and blood
  volume in the heart
• The pressure differences cause opening and
  closing of heart valves that allow one-way blood
  flow through heart
• Changes in pressure and blood volume correspond
  with electrical events on the EKG

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The Cardiac Cycle 5 Aspects

• Pump Cycle
• Phases of the pumping action of the heart
• Periods of valve opening and closure
• Changes in pressure within the atria and
  ventricles
• Changes in ventricular volume
• Reflect the amount of blood entering and leaving
  the ventricle during each heartbeat
• Heart sounds

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The Pump Cycle

• One complete cardiac cycle includes both
  contraction and relaxation of the atria and
  ventricles
• Two main stages
• Systole
• Contraction of a heart chamber forcing blood out
• Diastole
• Relaxation of a heart chamber allowing blood
  filling

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Phases of the Pump Cycle Phase 1 Mid-to-late
Diastole

• Two components
• Ventricular Filling
• Atrial Contraction

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Phases of the Pump Cycle Phase 1 Mid-to-late
Diastole

• Ventricular filling
• Ventricles are relaxed
• Intraventricular pressure is low
• AV valves are open
• Semilunar valves are closed
• Most ventricular filling is passive
• Passive blood flow from the atria into the
  ventricles accounts for about 70 - 80 of
  ventricular filling

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Phases of the Pump Cycle Phase 1 Mid-to-late
Diastole

• Atrial contraction
• Occurs following SA node depolarization
• Relatively little contribution to ventricular
  filling in normal, resting heart
• Atria contract and compress blood in the atria
• Slight rise in atrial pressure
• Last squirt of blood into ventricles
• Atria relax and are in atrial diastole for the
  rest of the cardiac cycle

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Phases of the Pump Cycle Phase 2 Systole

• Two components
• Isovolumetric Contraction
• Ventricular Ejection
• Atria are relaxed
• Ventricles are contracting
• Increase in ventricular pressure
• Pressure gradient exists between the ventricles
  and atria

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Phases of the Pump Cycle Phase 2 Systole

• Isovolumetric Contraction
• Ventricular contraction
• Increased ventricular pressure
• All four heart valves are momentarily closed
• When ventricular pressure exceeds atrial
  pressure, the AV valves close
• The semilunar valves remain closed until the
  ventricular pressure exceeds the pressure in the
  pulmonary trunk or aorta
• Once the ventricular pressure exceeds the
  pressure in the pulmonary trunk and aorta, the
  semilunar valves open
• Blood is ejected from the ventricles

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Phases of the Pump Cycle Phase 2 Systole

• Ventricular Ejection
• Begins when the semilunar valves open
• Blood is pumped out of the ventricles and into
  the pulmonary trunk and aorta
• Ventricular volume decreases

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Phases of the Pump Cycle Phase 3 Early Diastole

• Begins as ventricular contraction stops
• Two components
• Isovolumetric Relaxation
• Ventricular Filling Phase

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Phases of the Pump Cycle Phase 3 Early Diastole

• Isovolumetric relaxation
• Begins with ventricular relaxation
• Decreased ventricular pressure
• Semilunar valves close
• During this time, atria have been in diastole
• Filling with blood
• Increased atrial pressure

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Phases of the Pump Cycle Phase 3 Early Diastole

• Ventricular Filling
• In early diastole, the atrial blood pressure
  begins to exceed the pressure in the ventricles
• The AV valves open
• Blood flows from the atria into the ventricles
• Ventricular filling begins
• Mid-to-late Diastole (discussed earlier)
• Ventricles are relaxed
• AV valves are open
• Semilunar valves are closed

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Other Features of the Cardiac Cycle

• Quiescent period
• Follows ventricular systole
• The entire heart is relaxed for 0.4 sec
• Atrial systole lasts 0.1 sec
• Ventricular systole lasts 0.3 sec
• Note that pressure gradients keep blood moving
  one-way through heart and cause valve
  opening/closing

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Heart Sounds

• The heart sounds are triggered by valve closure
  and blood passing through the heart
• "Lub-Dup" produced by vibrations and turbulence
  created by blood flow inside the heart
• First sound is lub.
• Longer and louder
• Reflects AV valve closure
• Indicates the beginning of ventricular systole
• Second sound is dup.
• Shorter and sharp
• Reflects semilunar valve closure
• Indicates the beginning of ventricular diastole

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Cardiac Output and its Control

• Heart Rate (HR)
• The number of ventricular contractions per minute
• Stroke Volume (SV)
• The amount of blood pumped out of the ventricle
  with each contraction
• Stroke volume is usually about 80ml/beat at rest.

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Cardiac Output and its Control

• Cardiac Output (CO)
• The volume of blood pumped by each ventricular
  contraction per minute
• CO SV x HR
• Example (normal resting adult)
• SV 70 ml/beat and HR 72 bpm
• CO 70 ml/beat x 72 bpm 5,040 ml/min or about
  5 L/min
• At rest, CO is 5 L/min
• During stress such as exercise, the normal heart
  has the capacity to increase CO by 4 - 5 times
  that of resting
• 20 25 L/min
• Athletes can increase CO by as much as 7 times
  that of resting
• 35 L/min,
• This is known as the Cardiac Reserve

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Variables that Determine CO

• CO may be altered by changes in SV and/or HR
• Direct Relationship
• Heart Rate
• ? HR ? CO ? HR ? CO
• Stroke Volume
• ? SV ? CO ? SV ? CO

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Variables that Determine CO

• Force of heart muscle contraction (contractility)
• Factors that affect heart rate and contractility
• Extrinsic control Factors from outside of the
  heart
• Neural Input
• Circulating hormones (drugs, neurotransmitters,
  etc.)
• Intrinsic control Factors from within the heart
• Starlings Law of the Heart

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Factors Affecting CO Changes in HR

• Autonomic Control of HR
• Heart rate is influenced by 3 types of factors
• Sympathetic control
• Parasympathetic control
• Hormonal control
• Fibers of the ANS project to almost every part of
  the heart
• SA node
• AV node
• Ventricular myocardium
• The ANS regulates both HR and SV (contractility)

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Factors Affecting CO Changes in HR

• Sympathetic nervous system activation causes
• ? HR
• ? SV (contractility)
• Sympathetic input to the heart
• Sympathetic cardiac nerves emerge from the
  sympathetic trunk from thoracic region of spinal
  cord
• Provides innervations to the
• SA node
• AV node
• Ventricular myocardium
• Neurotransmitter is norepinephrine

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Factors Affecting CO Changes in HR

• Parasympathetic nervous system activation causes
• ? HR
• ? SV (contractility)
• Parasympathetic input to the heart
• The vagus nerve (X) emerges from the medulla
  oblongata
• Primarily innervates the
• SA node
• AV node
• Neurotransmitter is acetylcholine

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Sympathetic Control of HR

• Increased sympathetic activity
• Increases action potential frequency
• Action potential is transmitted faster
• Reduced delay of impulse conduction between the
  atria and ventricles
• Shortens the time it takes for action potentials
  to travel through the ventricles
• ? HR
• ? CO

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Parasympathetic Control of HR

• Increased parasympathetic activity
• Vagus Nerve Stimulation
• Decreases depolarization
• Decreases action potential frequency
• Action potential is transmitted slower
• Decreased conduction between atria and ventricles
  
• Lengthens the time it takes action potentials to
  travel through the ventricles
• ? HR
• ? CO

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Hormonal Control of HR

• Epinephrine (Catecholemines)
• Secreted by the adrenal medulla, usually in
  response to sympathetic nervous stimulation
• Travels through the bloodstream to the heart
• Exerts minute-by-minute control
• Increases the frequency of action potentials
  generated by the SA node, thus ? HR
• Increases speed of action potential conduction
  through heart, thus ? HR

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Hormonal Control of HR

• Thyroid Hormones (Thyroxine)
• Causes proliferation of adrenergic receptors, the
  binding sites for catecholamines resulting in
• ? HR
• ? SV
• ? CO
• Decreased total peripheral resistance (when
  present in very large amounts)
• Inadequate thyroid function can produce decreased
  HR, SV, and CO

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Integration of Heart Rate Control

• Three influences are active at all times
• Sympathetic
• Parasympathetic
• Hormonal
• Parasympathetic nervous control dominates the
  heart at rest
• Parasympathetic fibers are connected to the heart
  by the vagus nerve, which exerts beat-by-beat
  control of the SA and AV nodes
• Parasympathetic fibers release acetylcholine
• Vagal tone (suppressive effect)
• Acetylcholine inhibits the SA node and AV node
• Results in ? HR
• Decreased parasympathetic input
• Allows sympathetic input to dominate
• Results in ? heart rate

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Other Factors that Influence HR

• Age.
• HR is fastest in fetus (140 - 160 bpm)
• HR gradually decreases through childhood and most
  of adult life
• The elderly commonly develop tachycardia
• Gender.
• HR is faster in women (72 - 80 bpm) compared to
  men (64 - 72 bpm)
• Physical fitness.
• Highly-fit individuals have lower resting HR due
  to increased vagal tone and decreased sympathetic
  tone
• Body temperature.
• Increased body temperature (hyperthermia) as in
  fever or strenuous exercise increases HR
• Decreased body temperature (hypothermia)
  decreases HR
• Both conditions are associated with changes in
  metabolic rate of the myocardium

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Factors Affecting CO Changes in SV

• Ventricular Contractility
• The capacity of the ventricles to produce force
• Preload
• Also called End Diastolic Volume (EDV)
• The amount of blood in the heart at the end of
  ventricular filling
• Afterload
• Also called End Systolic Volume (ESV)
• The pressure the ventricles must overcome to
  eject blood out of the left ventricle

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The Influence of Ventricular Contractility on SV

• Contractility
• Any factor that causes an ? in contractility ?
  SV (? CO)
• Any factor that causes a ? in contractility ?
  SV (?CO)
• Control of Ventricular Contractility
• Sympathetic nervous system
• Hormonal

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The Influence of Ventricular Contractility on SV

• Sympathetic Nervous System Control
• Stimulation of cardiac muscle cells by
  sympathetic fibers results in the release of
  norepinephrine
• Norepinephrine
• Binds to beta adrenergic receptors on cardiac
  muscle cell membrane
• Stimulates a second messenger (cyclic AMP) to
  open Ca channels on the membrane
• ? Ca ? ventricular contractility
• ? SV
• ? CO

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The Influence of Ventricular Contractility on SV

• Hormonal Control
• Epinephrine circulating in the bloodstream binds
  to beta adrenergic receptors on cardiac muscle
  cells
• Epinephrine
• Stimulates second messengers (cyclic AMP) to open
  Ca channels on the membrane
• ? Ca ? ventricular contractility
• ? SV
• ? CO

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The Influence of Ventricular Contractility on SV

• Summary
• Contractility refers to force of contraction at
  any given preload
• The more blood in the ventricles at beginning of
  systole
• The greater the force of contraction
• the more blood ejected by the ventricles
• Results
• ? SV and ? CO
• ? Afterload (ESV)

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The Influence of Preload (EDV) on SV

• Starlings Law of the Heart
• When the rate at which blood flows into the heart
  from the veins (venous return) changes, the heart
  automatically adjusts its output to match the
  inflow.
• Starlings Law is based on the observed changes
  that occur in EDV and preload as a result of
  venous return
• This observation is called the Starling Effect

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Starlings Law of the Heart

• End diastolic volume (EDV)
• Determined by venous return, which is the amount
  of blood returned to the heart
• Influenced by central venous pressure
• ? EDV ? force of contraction (contractility)
• ? EDV ? SV
• ? EDV ? CO

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Starlings Law of the Heart

• Preload
• The amount of tension, or stretch, on the
  ventricular myocardium
• The cardiac muscle fibers are stretched due to
  the blood filling the chambers
• The effect of stretching ventricular walls ?
  force of ventricular contraction
• This is an example of intrinsic control of the
  heart

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Starlings Law of the Heart

• Starling Curves
• Within normal limits, any factor that increases
  venous return will result in
• ? preload (EDV)
• ? force of contraction
• Ultimately, ? SV

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Starlings Law of the Heart

• Starling Curves
• ? sympathetic input ? SV
• ? sympathetic input ? SV

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The Influence of Afterload (ESV) on SV

• Afterload
• The pressure the left ventricle must exceed
  before the aortic valve opens
• Indicates how hard the cardiac muscle must work
  to push blood into the arterial system
• Must push blood against the mean (average)
  arterial pressure
• ? mean arterial pressure ? afterload (ESV)
• Must push blood against the total peripheral
  resistance
• ? total peripheral resistance ? afterload (ESV)
• An Increased afterload (ESV) results in
• ? SV
• ? CO

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Heart Rate Abnormalities

• Tachycardia
• HR gt 100 bpm
• Causes
• Fever
• SNS stimulation
• Exercise
• Certain hormones
• Certain drugs

• Bradycardia
• HR lt 60 bpm
• Common in endurance-trained individuals
• Causes
• Hypothermia
• PNS stimulation
• Certain drugs

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Functional Human Physiologyfor the Exercise and
Sport Sciences The Cardiovascular System Blood

• Jennifer L. Doherty, MS, ATC
• Department of Health, Physical Education, and
  Recreation
• Florida International University

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The Functions of Blood

• Distribution and transport
• Delivers oxygen from lungs and nutrients from
  gastrointestinal tract to entire body
• Transfers metabolic waste products from cells to
  elimination sites (lungs and kidneys)
• Transports hormones from endocrine glands to
  target organs
• Maintenance of body temperature
• Absorbing and distributing metabolic heat
• Blood maintains temperature homeostasis with
  variable blood flow through the skin
• Regulation and maintenance of normal pH
• Buffers (proteins and ions)
• Maintenance of water content of cells with blood
  osmotic pressure
• Components of blood are involved in clot
  formation, thus preventing excessive blood/fluid
  loss
• Protection
• Blood carries components of the immune system to
  prevent infection

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Overview The Composition of Blood

• Blood is a fluid connective tissue composed of
• Organic (living) portion
• Cells or formed elements
• Erythrocytes
• Leukocytes
• Platelets
• Plasma proteins
• Inorganic (non-living) fluid matrix
• Plasma

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Plasma

• The liquid part of the blood
• Composed of water and a mixture of organic and
  inorganic substances
• 92 water
• 7 plasma proteins
• lt 1 other material
• Electrolytes, buffers, nutrients, gases,
  hormones, wastes, etc.
• Functions of plasma
• Transports nutrients and gases
• Regulates fluid and electrolyte balance
• Helps maintain stable pH

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Plasma

• Very similar to interstitial fluid, except with
  far more proteins
• Proteins remain in the plasma and cannot easily
  move into the interstitial space because of the
  structure of blood vessels
• Serum
• Plasma without plasma proteins

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Plasma Proteins

• Functions
• Maintain plasma osmotic pressure
• Very important for maintaining blood volume
• Maintain proper blood pH
• Accomplished through buffering action
• Able to take on and give up hydrogen ions
• Clotting
• Immunity

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Plasma Proteins - 3 Groups

• Albumins
• Comprise 55 of plasma proteins
• Functions
• Maintain osmotic pressure
• Transport hormones and fatty acids in the blood
• Globulins
• Comprise 36 of plasma proteins
• Functions
• Transport iron, fats, and fat-soluble vitamins in
  the blood.
• Gamma globulins function as antibodies in
  providing immunity
• Fibrinogen
• Comprises 7 of plasma proteins
• The largest plasma proteins, but least numerous
• Function
• Clotting

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Formed Elements

• All blood cells are the formed elements
• Erythrocytes (RBC)
• Leukocytes (WBC)
• Platelets
• Synthesized in bone marrow
• In children, the marrow of all bones produce
  blood cells
• In adults, only the marrow of the flat bones of
  the skull, sternum, pelvis, and the long bones of
  the upper limbs produce blood cells

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Erythrocytes (RBC)

• The RBC is one of the most specialized cell type
  in the body
• Adapted exclusively to produce and carry
  hemoglobin (Hb)
• Hb comprises 1/3 of the RBCs total weight
• In an adult male, there are 5 - 6 million
  RBCs/mm3
• 30 trillion RBCs circulating in blood
• Women and children have about 4.5 - 5 million
  RBCs/mm3

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Erythrocytes (RBC) - Characteristics

• Tiny size (8 microns) and flexible
• Able to pass through the narrow lumen of the
  smallest blood vessels
• Flexible, biconcave disks
• Thinner in the center than around edges
• Provides a large surface area, which aids gas
  diffusion in and out of the RBC
• No nucleus or other organelles
• Unable to synthesize proteins, grow, or reproduce
  
• Glucose is the only fuel source for RBCs
• Do not use any of the oxygen they carry

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Hemoglobin (Hb)

• Hb is the oxygen carrying component of RBCs
• Hb binds reversibly to oxygen
• Hemoglobin is found in two forms
• Oxyhemoglobin
• Gives blood its bright red color.
• Hb O2 gt HbO2
• Deoxyhemoglobin
• Has a dark red color and gives veins a bluish
  tint
• HbO2 gt Hb O2

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Hemoglobin (Hb)

• Hb is composed of 4 globin molecules
• Each globin molecule contains a heme group
• Globin Molecule
• The protein portion of the Hb molecule
• Composed of four polypeptide chains
• Each of the 4 globin chains is bound to a heme
  group
• Heme Group
• The non-protein pigment containing iron Fe2
• Heme is the red part of red blood cells
• Each heme can bind reversibly with one oxygen
  molecule
• Thus, each Hb molecule can carry four molecules
  of O2

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Leukocytes (WBC)

• Represent only 1 of total blood volume
• But, WBCs are a crucial component of the immune
  system
• WBCs are similar to RBCs in the following ways
• Synthesized in bone marrow
• WBCs are unlike RBCs the following ways
• Contain a nucleus and organelles
• Do not contain hemoglobin
• Not always contained in blood vessels
• Diapedesis
• WBCs are able to move in and out of blood vessels
  with amoeboid motion
• Chemotaxis
• WBCs follow a chemical trail leading to the site
  of tissue damage

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Leukocytes (WBC) 2 Groups

• Classified based on structure and function
• Granulocytes
• Lobed nuclei
• Obvious cytoplasmic granules
• Very short average life span, about 12 hours
• Agranulocytes
• Spherical or oval nuclei
• Lack obvious cytoplasmic granules
• Relatively long life span, greater than 12 hours

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Platelets (Thrombocytes)

• Anucleate cell fragments
• Incomplete cells
• Formed from the fragments of a larger cell, a
  megakaryocyte
• Magakaryocytes are derived from stem cells in
  bone marrow
• Brief life span of about 10 days
• Contain many cytoplasmic granules
• These granules are loaded with enzymes
• Function
• Stop bleeding through the process of hemostasis

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Platelets and Hemostasis

• Stop bleeding in small blood vessels or in
  superficial cuts by
• Physically plugging breaks in blood vessel
  walls
• Releasing chemicals that promote blood clotting
• Involves 3 phases that occur in rapid sequence
• Vascular Spasm
• Platelet Plug Formation
• Formation of a Blood Clot

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Vascular Spasm (Vasospasm)

• The contraction of smooth muscle in the walls of
  small blood vessels resulting in vasoconstriction
  
• Lasts only short time, around 20 - 30 minutes at
  most
• Within 20 30 minutes, a platelet plug has
  formed
• Vasoconstriction results in
• Narrowing of the lumen
• Increased resistance to blood flow
• Reduced blood loss
• Vascular Spasm may be stimulated by
• Damage, breaking or cutting of a blood vessel
• The release of local pain receptors

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Platelet Plug Formation

• Normally, platelets do not stick to each other or
  to blood vessel walls
• Platelets do stick however, to the rough edges
  of a damaged blood vessel
• Platelets are attracted to the collagen in the
  vessel wall that is exposed when the vessel is
  damaged
• 2 components to platelet plug formation
• Platelet adhesion
• Platelet aggregation

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Platelet Plug Formation

• Platelet adhesion
• Platelets adhere to the rough edges or underlying
  endothelium of a damaged blood vessel
• Von Willebrand factor (vWf)
• Protein secreted by magakaryocytes, platelets,
  and endothelial cells lining blood vessels
• It is present in plasma and accumulates at the
  site of blood vessel damage
• It binds to the exposed collagen of a damaged
  blood vessel
• Causes platelets to attach to the damaged area as
  well
• Activates platelets
• Causes platelets to swell, become sticky, and
  develop spiky projections

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Platelet Plug Formation

• Platelet Aggregation
• Occurs as the platelets begin to release chemical
  mediators
• ADP, thromboxane A2, epinephrine, and serotonin
• ADP
• Causes the platelets to aggregate, forming a
  platelet plug
• Aggregated or accumulated platelets stimulate the
  secretion of more ADP, a positive feedback loop
• ADP also causes the release of thromboxane A2
• Thromboxane A2
• Formed from arachidonic acid, which is found in
  the membranes of platelets
• Slows blood flow and attract platelets to the
  area
• Epinephrine, serotonin, and thromboxane A2 act as
  vasoconstrictors to continue the vascular spasms.

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Platelet Plug Formation

• A positive feedback loop
• The cycle is initiated and results in rapid
  formation of a platelet plug
• Within one minute, enough platelets have
  accumulated at the injury site to form a platelet
  plug
• The platelet plug reduces blood loss from small
  blood vessels, but a large blood clot may be
  required to completely stop bleeding

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Formation of a Blood Clot

• Also called coagulation
• A blood clot is the result of many clotting
  factors
• Most clotting factors are plasma proteins
• There are 30 different clotting factors in the
  blood that affect the coagulation process
• Clot formation
• Depends on the balance between clotting factors
  that promote clotting (procoagulants) and those
  that inhibit clotting (anticoagulants)

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Formation of a Blood Clot

• Procoagulants
• Enhance blood clotting, or coagulation
• Mostly produced by the liver
• Anticoagulants
• Inhibit blood clotting
• Heparin
• Produced by basophils
• Inactivates thrombin or prostaglandin 12
• Prostaglandin I2 (PGI2) and nitric oxide (NO)
• Produced and continually released by healthy
  vascular endothelial cells.
• Repel platelets, thus preventing platelet
  adhesion
• Normally, anticoagulants dominate over
  procoagulants. But with vessel injury,
  procoagulant activity increases dramatically at
  the site of vascular damage resulting in blood
  clot formation.

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Formation of a Blood Clot A 6 step process

• Step 1. Prothrombin Activation
• Prothrombin activation may be accomplished via 2
  pathways
• Extrinsic pathway
• It is a rapid, shortcut pathway that occurs
  within seconds if damage is severe
• Coagulation factor III is released by damaged
  vessels
• Cascade of coagulation factors are activated,
  ultimately leading to the activation of thrombin
• Intrinsic pathway
• It occurs slowly, requiring several minutes
• Coagulant factor XII (also called Hageman factor)
  is activated
• Cascade of coagulation factors are activated,
  ultimately leading to the activation of thrombin
• This is usually the slowest step in the clotting
  process

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Formation of a Blood ClotA 6 step process

• Step 2. Conversion of Prothrombin to Thrombin
• Prothrombin activator
• An enzyme that catalyzes a series of chemical
  reactions that convert prothrombin to thrombin
• Prothrombin
• An inactive plasma protein produced in the liver
• Thrombin
• The active from of an enzyme that converts
  fibrinogen to fibrin

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Formation of a Blood ClotA 6 step process

• Step 3. Conversion of Fibrinogen to Fibrin
• Occurs in a chemical reaction catalyzed by
  thrombin
• Fibrinogen
• A soluble plasma protein that forms blood clots
  when activated by thrombin
• Fibrin
• An insoluble, elastic protein composed of many
  fibrinogen units joined end to end
• Fibrin forms a network of long threads, forming
  the blood clot
• Fibrin threads trap blood cells, platelets, and
  plasma to strengthen and stabilize the clot

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Formation of a Blood ClotA 6 step process

• Step 4. Clot Retraction
• After clot formation, the platelets begin to
  contract
• Platelets contain actin and myosin
• Retraction draws the injured edges of the blood
  vessel into close proximity
• Prevents further blood loss
• Retraction squeezes serum out of the platelets
• Platelets shrink after the blood clot forms

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Formation of a Blood ClotA 6 step process

• Step 5. Repair
• While the clot is retracting, platelets release
  Platelet Derived Growth Factor (PDGF)
• PDGF stimulate fibroblasts and endothelial cells
• Fibroblasts and endothelial cells in the vessel
  wall are stimulated by PDGF to
• Reproduce
• Repair the damaged blood vessel wall
• Ultimately, the clot dissolves as the tissue heals

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Formation of a Blood ClotA 6 step process

• Step 6. Fibrinolysis
• Clot breakdown
• Coincides with repair of the blood vessel wall
• Tissue plasminogen activator (tPA)
• Released by blood cells or endothelial cells
• Converts plasminogen to its active form, plasmin
• Plasminogen
• An inactive plasma protein enzyme
• Plasmin
• Breaks down fibrin
• Inactivates certain coagulation factors
• Dissolves the blood clot
• Occurs usually within a few days after the blood
  clot forms

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Functional Human Physiologyfor the Exercise and
Sport Sciences The Cardiovascular System Blood
Vessels, Blood Flow, and Blood Pressure

• Jennifer L. Doherty, MS, ATC
• Department of Health, Physical Education, and
  Recreation
• Florida International University

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Physical Laws Governing Blood Flow and Blood
Pressure

• The goal of the cardiovascular system is to
  maintain adequate blood flow through peripheral
  tissues and organs
• General principles govern how pressure gradients
  and resistance affect blood flow

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Pressure Gradients

• Pressure Gradient
• Defined as the difference in pressure from one
  region of the vascular system to another
• Specifically, it is the force exerted (per unit
  area) by the blood against the inner walls of the
  blood vessels
• Blood always flows from regions of high pressure
  to regions of low pressure
• If there is no pressure gradient, no blood will
  flow
• Blood pressure is directly generated by the
  pumping action of the heart.

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Pressure Gradients

• Systemic Blood Pressure
• Expressed in terms of millimeters of mercury (mm
  Hg)
• Blood pressure of 120 mm Hg would be equal to the
  pressure exerted by a column of mercury 120 mm
  high
• Systolic blood pressure (SBP)
• The maximum blood pressure generated during
  ventricular contraction (systole)
• Diastolic blood pressure (DBP)
• The lowest blood pressure that remains in the
  arteries during ventricular relaxation (diastole)

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Pressure Gradients

• Pulse
• A physical event due to alternating expansion and
  contraction of the arteries
• The pulse can be palpated at certain places on
  the body where the arteries are close to the
  surface
• Pulse pressure (PP)
• The arithmetic difference between SBP and DBP
• PP SBP - DBP
• It is a calculated figure not a physical event

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Pressure Gradients

• Mean Arterial Pressure (MAP)
• The driving pressure in the arterial system that
  keeps blood flowing
• A weighted average of systemic blood pressure to
  account for the heart spending more time in
  diastole
• NOT the arithmetic average of SBP and DBP
• MAP DBP 1/3 (SBP - DBP)
• Changes in MAP occur due to
• Abnormal increases in blood volume
• Increased salt intake
• Abnormal decreases in blood volume
• Dehydration
• Hemorrhage

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Pressure Gradients

• Any factor that alters blood volume will affect
  BP
• The volume of the blood in the arteries is
  directly proportional to BP
• A hemorrhage causing a loss in blood volume will
  cause a decrease in BP
• The restoration of BP, such as during a blood
  transfusion, will increase the volume of blood
  thereby increasing BP

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Resistance in the Cardiovascular System

• Peripheral Resistance
• The force that opposes blood flow
• Caused by friction between the blood and the
  walls of the blood vessel
• In order for blood to flow, BP must be greater
  than the peripheral resistance
• BP decreases as the distance from the left
  ventricle increases
• The greatest decrease in BP occurs across the
  arterioles because these blood vessel offer the
  greatest resistance to blood flow
• Blood pressure continues to decrease as blood
  flows through capillaries and the venous system

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Sources of Peripheral Resistance

• 3 main sources of peripheral resistance
• Blood Viscosity
• Refers to the "stickiness" or thickness of the
  blood
• Vessel Length
• Vessel Radius

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Blood viscosity

• Blood viscosity is related to the density of
  blood cells in the plasma
• There is a direct relationship between blood
  viscosity and peripheral resistance
• ? viscosity ? peripheral resistance ?
  viscosity ? peripheral resistance
• There is an inverse relationship between blood
  viscosity and blood flow (impedes blood flow)
• ? viscosity ? blood flow ? viscosity ? blood
  flow
• In healthy people, blood viscosity varies little
• Any condition that increases or decreases the
  concentration of blood cells or plasma proteins
  may alter blood viscosity
• Anemia or hemorrhage ? blood viscosity
• High altitude or dehydration ? blood viscosity

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Vessel Length

• There is a direct relationship between vessel
  length and resistance to blood flow
• The greatest effect of vessel length on
  peripheral resistance is found in the blood
  vessels of the systemic circuit
• Blood vessels in the pulmonary circuit are
  shorter (and more elastic)
• Therefore, resistance to blood flow in the
  pulmonary circuit is lower in comparison to the
  systemic circuit
• Vessel length does not vary much in adults

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Vessel Diameter

• Vessel diameter is associated with the amount of
  friction between the blood and the walls of blood
  vessel
• Blood flowing close to the wall of the blood
  vessel is slowed due to friction
• Blood flowing down the center of a blood vessel
  meets less friction, therefore blood flows faster
  
• Large-diameter vessels offer less resistance to
  blood flow
• More blood is able to flow down the center of the
  blood vessel
• Small-diameter vessels offer greater resistance
  to blood flow
• More blood is in contact with the wall of the
  blood vessel

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Central Venous Pressure

• Corresponds with the pressure in the right atrium
• Central venous pressure is measured in the right
  atrium because all of the veins in the systemic
  circuit empty into this heart chamber
• Blood pressure decreases as it flows out of the
  arterial circulation and into the venous
  circulation

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Central Venous Pressure

• Venous blood flow is maintained via
• Respiratory pump
• Depends on pressure changes in the ventral body
  cavity associated with breathing
• It helps to move blood upward toward the heart
• Muscle pump
• Even more important
• Skeletal muscle contractions function to milk
  blood back to heart

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Movement of Fluid Across Capillary Walls

• 2 purposes
• To exchange nutrients, gases, and metabolic
  byproducts between blood and cells
• This is impossible in arteries and veins because
  the vessel walls are too thick to allow rapid
  diffusion
• To maintain normal distribution of the
  extracellular fluid

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Movement of Fluid Across Capillary Walls

• Forces that drive movement of fluid in and out of
  capillaries are called, Starling Forces
• Capillary exchange is made possible by three
  forces at work simultaneously
• Diffusion
• Filtration
• Osmosis

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Diffusion

• The most important method of capillary exchange
• Accounts for the exchange of oxygen and most
  nutrients such as amino acids, fatty acids, and
  glucose, carbon dioxide, hormones, etc.
• Diffusion occurs along the entire length of the
  capillary bed
• Solutes move down their concentration gradient
  from areas of higher concentration to areas of
  lower concentration.
• For example, oxygen and nutrients diffuse from
  the blood into cells
• Conversely, carbon dioxide and metabolic waste
  products diffuse from the cells into the blood
• The direction and magnitude of water movement
  across capillary walls depends on the balance
  between hydrostatic pressures and osmotic
  pressures

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Filtration

• The movement of fluids through a capillary wall
  is due to hydrostatic pressure
• The force exerted by a fluid pushing against a
  wall
• In capillaries, hydrostatic pressure is the
  capillary BP
• Capillary BP is influenced by
• Arterial pressures
• Venous pressures
• Resistance in the pre- and post-capillary
  sphincters
• Filtration occurs primarily at the arterial end
  of the capillary where hydrostatic pressure is
  high, and decreases along the length of the
  capillary as hydrostatic pressure decreases
• Filtration is a passive process accounting for
  movement of solutes such as ions

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Osmosis

• Water movement from an area of lower solute
  concentration to an area of higher solute
  concentration
• Occurs in response to oncotic pressure
• Osmotic pressure exerted by proteins
• Plasma proteins (mainly albumin) are large, lipid
  insoluble particles that do not leave the blood
  in capillaries
• Osmotic pressure in capillaries does not change
  along the length of vessels
• Plasma proteins remain in the capillaries,
  exerting a fixed amount of osmotic pressure along
  its entire length
• Plasma proteins create an osmotic pressure
  greater than the osmotic pressure of the
  interstitial fluid
• Therefore, blood in the capillary has a greater
  attraction for water than does interstitial fluid

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Starling Forces

• Forces driving fluid into and out of the
  capillaries
• These forces are balanced and counteracted by
  high capillary hydrostatic pressure and osmotic
  pressures
• Net filtration pressure (NFP)
• The net effect of all the forces driving fluid
  across the capillary walls
• NFP (forces that promote filtration) - (forces
  that oppose filtration)

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Starling Forces

• Forces that promote filtration and drive fluids
  out of the capillary are
• Capillary hydrostatic pressure
• Interstitial fluid osmotic pressure
• Forces that promote fluid absorption and pull
  fluids into the capillary are
• Capillary osmotic pressure
• Interstitial fluid hydrostatic pressure
• Net Movement
• Usually more fluid leaves the capillary at the
  arterial end than returns at the venous end
• Excess fluid is collected by the lymphatic system
  and returned to the systemic circulation.

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The Lymphatic System

• A pump-less system that transports body fluids
• Functions
• Maintain fluid balance
• Drains tissue spaces of excess interstitial fluid
• Defend body against disease (immunity)
• Produces and maintains lymphocytes
• Transport dietary fats (digestion)
• Carries lipids (and lipid soluble vitamins) from
  their site of absorption in the GI tract to the
  blood

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Lymph and Lymphoid Tissue

• Lymph
• Tissue fluid that has entered a lymph capillary
• Contains mostly water
• Also contains other dissolved solutes that were
  diffused or filtrated out of the blood into the
  interstitial fluid
• Interstitial fluid forms when plasma is filtered
  out of capillaries at the arterial end of
  capillary bed
• Formation