Cardiovascular+Physiology Circuitry%2C+Hemodynamics%2C+Electrophysiology
Transcript of Cardiovascular+Physiology Circuitry%2C+Hemodynamics%2C+Electrophysiology
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Cardiovascular Physiology:
Circuitry, Hemodynamics, Electrophysiology
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Overview: Cardiovascular System
Functions of CV system Deliver blood to tissues
Provides nutrients to cells for metabolism
Removes wastes from cells
Components: Blood Vessels
Heart
Blood vessels: Arteries
Arterioles
Capillaries
Venules
Veins
Divisions:
Systemic circulation:
Left heart
Left ventricle pumps blood to all organs EXCEPT lungs
Pulmonary circulation:
Right heart
Right ventricle pumps blood to lungs
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Overview: The Heart
Two functional halves Atria
Ventricles
Wall of heart
Myocardium Cardiac muscle
Inside pericardium
Valves Atrioventricular:
Tricuspid valve (right)
Bicuspid valve (left)
Semilunar: Pulmonary valve (right)
Aortic valve (left)
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Circuitry
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Circuitry of Blood Flow
Sequential blood flow: Left heartsystemic circulationright
heartpulmonary circulationleft heart
Blood oxygenated in lungs returns to leftatrium via pulmonary vein
Blood flows from left atrium to leftventricle through mitral valve (AV valve)
Oxygenated blood fills left ventricle
Blood leaves left ventricle through aorticvalve into aorta
Blood flows through arterial system
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Circuitry of Blood Flow
Cariac output distributed among organs
Blood flow from organs collected in veinsvenacava
Vena cava carriers blood to right heart
Right atrium fills with blood (venous return)
Venous blood flows from fight atrium to rightventricle via tricuspid valve (AV valve)
Blood ejected from right ventricle into pulmonary
artery through pulmonary valve
Blood flows through pulmonary artery to lungs,where blood is oxygenated (CO2 removed)
Oxygenated blood returned to left atrium viapulmonary veins
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Left and Right Heart
Cardiac output
Rate blood is pumped from either ventricle
Cardiac output of left ventricle = cardiac output of rightventricle
Venous return
Rate blood is returned to atria from veins
Venous return to left heart = venous return to right heart
Cardiac output from heart = venous return to heart
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Hemodynamics
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Blood Flow, Pressure, & Resistance
Similar to current, voltage, and resistance in electricalcircuits Ohms Law: I = V/R
Q = P/R Q = flow (mL/min)
P = pressure difference (mm Hg)
R = resistance (mm Hg/mL/min)
Direction of blood flow determined by direction of pressuregradient (high to low pressure)
Major mechanism for changing blood flow: changing R in
blood vessels R = P/Q
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Resistance to Blood Flow
Poiseuille equation: R = resistance
= viscosity of blood
L = length of blood
vessel r4 = most important
relationship to R
Q =Pr4
8nl
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Series Resistance
Arteries, arterioles, capillaries, venules, and
veins are arranged in series
Total R = sum of individual Rs
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Parallel Resistance
Arteries branch to servemany organs Each organ can regulate its
own blood flow
Total R in parallel < anyindividual Rs
Flow through each organ isa fraction of total flow
Adding another R to circuitdecrease in total R
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Viscosity of Blood
Primarily due to RBCs
Hematocrit
% of blood that is cells
Greater %greater viscosity
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Laminar Flow
Laminar flow:
Parabolic profile of velocity
Layer of blood next to wall adheres to it
Velocity of flow at vessel wall is 0, velocity flow at center is maximal
Turbulent flow
Irregularity in blood vessel
Requires more energy to move
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Reynolds Number
Predicts whether blood flow
will be turbulent
= blood density
d = blood vessel diameter
v = blood flow velocity
= blood viscosity
If NR< 2000
laminar flow
Example: Anemia
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Pressure Profile of Vasculature Aorta: high P
Cardiac output
Low compliance of arterial wall
Large arteries: high P High elastic recoil of arterial walls
Small arteries: decreasing arterial P
Arterioles: dramatic decrease in P High resistance to flow
Capillaries: further decease in P Frictional resistance to flow
Filtration of fluid out
Venules & veins: further decrease in P High compliance and large diameters
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Cardiac Electrophysiology
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Cardiac Muscle
All contractile cardiac muscle cells contract onevery heart beat
Excitable
Excitation-contraction coupling
Innervation Sympathetic
Innervates entire heart
Releases norepinephrine Binds B receptors
Parasympathetic Innervates only specific parts of heart
Releases ACh Binds muscarininc Rs
Blood supply: Coronary blood supply (from systemic arteries)
Cardiac muscle as a syncytium
Gap junctions: cells so
interconnected that when one cell
becomes excited, the AP spreads to
all of them
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Cardiac Electrophysiology:General Review
Heart as a pumpventriclesmust be electrically activated tocontract:
Initiation of action potentials fromSA node
APs then conducted to entire
myocardium
Contraction
Cardiac muscle as a syncytium
Gap junctions: cells so
interconnected that when one cell
becomes excited, the AP spreads to
all of them
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Cardiac Action Potentials
Two kinds of heart cells:1. Contractile
Atria and ventricles
APs lead tocontraction and
generation offorce/pressure
2. Conducting SA node, AV node,
bundle of His, Purkinje
system Rapidly spread APs
over entiremyocardium
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Sequence of Excitation
Pathway of action potentials in heart:
1. SA node Where AP is initiated
Self-excitable
Pacemaker
2. Internodal tracts Conducts impulse from SA node to AV node and
throughout atria
3. AV node Slow conductiondelay
Diminished number of gap junctions
4. Bundle of His Conducts impulse from atria to ventricles
5. Purkinje system Conducts impulse to all parts of ventricles
Fast conduction
Increased gap junctions
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Normal Sinus Rhythm
Three requirements
AP must originate in SA node
SA nodal impulses must occur regularly at a rate of
60-100 impulses per minute
Activation of myocardium must occur in correct
sequence and with correct timing
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APs in Ventricles and Atria
Long duration
Long refractory period
Stable resting membranepotential
Plateau Sustained period of
depolarization
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Phases of Action Potentials:Ventricles and Atria
Phase O, Upstroke Rapid depolarization
Na+ inward current through fast Na+ channels
Phase 1, Initial Repolarization Inactivation gates close on fast Na+ channels
K+ moves out due to electrochemical gradient(leak channels)
Phase 2, Plateau Activation of slow Ca2+ channels
Ca2+ moving in balances K+ moving out
Phase 3, Repolarization Inactivation of slow Ca2+ channels
Opening of voltage-gated K+ channels
Phase 4, Resting Membrane Potential Voltage-gated K+ channels close
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Action Potentials in SA Node Differences:
Automaticity
Unstable resting membrane potential
No sustained plateau
Phases: Phase 0: upstroke
Activation of voltage-gated Ca2+ channels
Phase 3: repolarization Opening of voltage-gated K+ channels
Inactivation of voltage-gated Ca2+ channels
Phase 4: spontaneous depolarization(Pacemaker potential)
Slow closing of voltage-gated K+ channels
Inward Na+ current = If (slow movement of Na+to inside) The rate of Phase 4 sets
the heart rate
Na+ Ca2+ K+
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Latent Pacemakers
Automaticity (phase 4 depolarization) AV node
Bundle of His
Purkinje fibers
Overdrive suppression SA node has fastest firing rate
SA node drives other firing rates
Spontaneous depolarization is suppressed
Ectopic pacemaker: SA node firing rate decreases or stops
Latent pacemaker firing rate increases
Conduction of APs from SA node is blocked
Location Firing Rate
(impulses/min)
SA Node 70-80
AV node 40-60
Bundle of His 40
Purkinje fibers 15-20
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Excitation-
Contraction Coupling
AP initiated in myocardial cell membrane
Depolarization spreads to interior of cell viaT-tubules
Inward Ca2+ current from T-tubules (throughL-type channels)
Calcium-Induced Calcium Release: Inward Ca2+ current Initiates release of more
Ca2+ from SR Through Ca2+ release channels (ryanodine
receptors)
Ca2+ binds troponin Ctropomyosin movedcross-bridge formation
Cross-bridge cycling Continues as long as there is enough intracellular
Ca2+