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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    2

    8

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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

    4

    8

    5

    6

    7

    3

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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+