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Biol 155 Human Physiology

VIEWS: 9 PAGES: 96

									                 Cardiac Muscle

   Found only in heart
   Striated
   Each cell usually has one nucleus
   Has intercalated disks and gap junctions
   Autorhythmic cells
   Action potentials of longer duration and longer
    refractory period
   Ca2+ regulates contraction
                        Cardiac Muscle




   Elongated, branching cells containing 1-2 centrally located nuclei
   Contains actin and myosin myofilaments
   Intercalated disks: Specialized cell-cell contacts
   Desmosomes hold cells together and gap junctions allow action potentials
   Electrically, cardiac muscle behaves as single unit
Cardiac myocyte action potential:
              Refractory Period

   Absolute: Cardiac muscle cell completely
    insensitive to further stimulation
   Relative: Cell exhibits reduced sensitivity to
    additional stimulation
   Long refractory period prevents tetanic
    contractions
AP-contraction relationship:
               AP in skeletal muscle is very
                short-lived
                   AP is basically over before an
                    increase in muscle tension can
                    be measured.


               AP in cardiac muscle is very
                long-lived
                   AP has an extra component,
                    which extends the duration.
                   The contraction is almost over
                    before the action potential has
                    finished.
          Functions of the Heart
   Generating blood pressure
   Routing blood
       Heart separates pulmonary and systemic
        circulations
   Ensuring one-way blood flow
       Heart valves ensure one-way flow
   Regulating blood supply
       Changes in contraction rate and force match
        blood delivery to changing metabolic needs
Orientation of cardiac muscle fibres:
                       Unlike skeletal muscles,
                        cardiac muscles have to
                        contract in more than
                        one direction.
                       Cardiac muscle cells are
                        striated, meaning they
                        will only contract along
                        their long axis.
                       In order to get
                        contraction in two axis,
                        the fibres wrap around.
Circulation circuits:
                  Heart Wall

   Three layers of tissue
     Epicardium: This serous membrane of smooth
      outer surface of heart
     Myocardium: Middle layer composed of cardiac
      muscle cell and responsibility for heart
      contracting
     Endocardium: Smooth inner surface of heart
      chambers
Valve function:
Coronary circulation:
Cardiac conducting system:
Pacemaker potential:
EKG:
Heart sounds:
                    Heart Sounds

   First heart sound or “lubb”
       Atrioventricular valves and surrounding fluid vibrations
        as valves close at beginning of ventricular systole
   Second heart sound or “dupp”
       Results from closure of aortic and pulmonary semilunar
        valves at beginning of ventricular diastole, lasts longer
   Third heart sound (occasional)
       Caused by turbulent blood flow into ventricles and
        detected near end of first one-third of diastole
          Cardiac Arrhythmias

   Tachycardia: Heart rate in excess of 100bpm
   Bradycardia: Heart rate less than 60 bpm
   Sinus arrhythmia: Heart rate varies 5% during
    respiratory cycle and up to 30% during deep
    respiration
   Premature atrial contractions: Occasional
    shortened intervals between one contraction
    and succeeding, frequently occurs in healthy
    people
                 Cardiac Cycle

   Heart is two pumps that work together, right
    and left half
   Repetitive contraction (systole) and relaxation
    (diastole) of heart chambers
   Blood moves through circulatory system
    from areas of higher to lower pressure.
       Contraction of heart produces the pressure
Pressure relationships:
    Mean Arterial Pressure (MAP)
   Average blood pressure in aorta
   MAP=CO x PR
       CO is amount of blood pumped by heart per minute
            CO=SV x HR
                 SV: Stroke volume of blood pumped during each heart beat
                 HR: Heart rate or number of times heart beats per minute
            Cardiac reserve: Difference between CO at rest and
             maximum CO
       PR is total resistance against which blood must be
        pumped
Factors Affecting MAP
          Regulation of the Heart
   Intrinsic regulation: Results from normal functional
    characteristics, not on neural or hormonal regulation
       Starling’s law of the heart
   Extrinsic regulation: Involves neural and hormonal
    control
       Parasympathetic stimulation
            Supplied by vagus nerve, decreases heart rate, acetylcholine
             secreted
       Sympathetic stimulation
            Supplied by cardiac nerves, increases heart rate and force of
             contraction, epinephrine and norepinephrine released
              Heart Homeostasis
   Effect of blood pressure
       Baroreceptors monitor blood pressure
   Effect of pH, carbon dioxide, oxygen
       Chemoreceptors monitor
   Effect of extracellular ion concentration
       Increase or decrease in extracellular K+ decreases heart
        rate
   Effect of body temperature
       Heart rate increases when body temperature increases,
        heart rate decreases when body temperature decreases
Baroreceptor and Chemoreceptor
           Reflexes
  Cardian
innervation:
               Pacemaker regulation:




   Once the pacemaker cells reach threshold, the
    magnitude and duration of the AP is always the same.
   In order to change the frequency, the time between
    APs must vary.
       The interval can only be changed in two ways.
            The rate of depolarization can be changed
            The amount of depolarization required to reach threshold can be
             changed.
Vascular physiology:
    Peripheral Circulatory System
   Systemic vessels
       Transport blood through most all body parts
        from left ventricle and back to right atrium
   Pulmonary vessels
       Transport blood from right ventricle through
        lungs and back to left atrium
   Blood vessels and heart regulated to ensure
    blood pressure is high enough for blood flow
    to meet metabolic needs of tissues
          Blood Vessel Structure
   Arteries
       Elastic, muscular, arterioles
   Capillaries
     Blood flows from arterioles to capillaries
     Most of exchange between blood and interstitial
      spaces occurs across the walls
     Blood flows from capillaries to venous system

   Veins
       Venules, small veins, medium or large veins
Structure of Arteries and Veins
                   Three layers except for
                    capillaries and venules
                   Tunica intima (interna)
                       Endothelium
                   Tunica media
                       Vasoconstriction
                       Vasodilation
                   Tunica adventitia (externa)
                       Merges with connective
                        tissue surrounding blood
                        vessels
                       Note mistake on figure
              Structure of Arteries

   Elastic or conducting arteries
       Largest diameters, pressure high and fluctuates
   Muscular or medium arteries
       Smooth muscle allows vessels to regulate blood
        supply by constricting or dilating
   Arterioles
       Transport blood from small arteries to capillaries
              Structure of Veins
   Venules and small veins
       Tubes of endothelium on delicate basement
        membrane
   Medium and large veins
   Valves
       Allow blood to flow toward heart but not in
        opposite direction
   Atriovenous anastomoses
       Allow blood to flow from arterioles to small
        veins without passing through capillaries
Blood Vessel Comparison:
        Capillaries:
   Capillary wall consists
    mostly of endothelial
    cells
   Types classified by
    diameter/permeability
       Continuous
            Do not have fenestrae
       Fenestrated
            Have pores
       Sinusoidal
            Large diameter with large
             fenestrae
Capillary Network:
              Blood flows from
               arterioles through
               metarterioles, then
               through capillary
               network
              Venules drain network
              Smooth muscle in
               arterioles, metarterioles,
               precapillary sphincters
               regulates blood flow
Muscular contractions aid venous return:
          Pulmonary Circulation

   Moves blood to and from the lungs
   Pulmonary trunk
       Arises from right ventricle
   Pulmonary arteries
       Branches of pulmonary trunk which project to
        lungs
   Pulmonary veins
       Exit each lung and enter left atrium
     Systemic Circulation: Arteries

   Aorta
     From which all arteries are derived either directly or
      indirectly
     Parts
            Ascending, descending, thoracic, abdominal
   Coronary arteries
       Supply the heart
     Systemic Circulation: Veins
   Return blood from body to right atrium
   Major veins
     Coronary sinus (heart)
     Superior vena cava (head, neck, thorax, upper
      limbs)
     Inferior vena cava (abdomen, pelvis, lower limbs)

   Types of veins
       Superficial, deep, sinuses
    Dynamics of Blood Circulation

   Interrelationships between
     Pressure
     Flow

     Resistance

     Control mechanisms that regulate blood pressure

     Blood flow through vessels
               Blood Pressure

   Measure of force exerted by blood against the
    wall
   Blood moves through vessels because of blood
    pressure
   Measured by listening for Korotkoff sounds
    produced by turbulent flow in arteries as
    pressure released from blood pressure cuff
Pressure and Resistance
                 Blood pressure averages
                  100 mm Hg in aorta and
                  drops to 0 mm Hg in the
                  right atrium
                 Greatest drop in
                  pressure occurs in
                  arterioles which regulate
                  blood flow through
                  tissues
                 No large fluctuations in
                  capillaries and veins
Blood Pressure Measurement
Pulse Pressure
            Difference between
             systolic and diastolic
             pressures
            Increases when stroke
             volume increases or
             vascular compliance
             decreases
            Pulse pressure can be
             used to take a pulse to
             determine heart rate
             and rhythmicity
     Blood Flow, Poiseuille’s Law
            and Viscosity
   Blood flow                         Poiseuille’s Law
       Amount of blood moving             Flow decreases when
        through a vessel in a               resistance increases
        given time period                  Flow resistance
                                            decreases when vessel
       Directly proportional to            diameter increases
        pressure differences,
        inversely proportional to      Viscosity
        resistance                         Measure of resistance of
                                            liquid to flow
                                           As viscosity increases,
                                            pressure required to
                                            flow increases
    Critical Closing Pressure,
  Laplace’s Law and Compliance
Critical closing pressure            Vascular compliance
      Pressure at which a blood           Tendency for blood
       vessel collapses and blood           vessel volume to
       flow stops                           increase as blood
                                            pressure increases
                                           More easily the vessel
Laplace’s Law                               wall stretches, the
      Force acting on blood                greater its compliance
       vessel wall is proportional         Venous system has a
       to diameter of the vessel            large compliance and
       times blood pressure                 acts as a blood reservoir
        Physiology of Systemic
             Circulation
   Determined by
     Anatomy of circulatory system
     Dynamics of blood flow

     Regulatory mechanisms that control heart and
      blood vessels
   Blood volume
     Most in the veins
     Smaller volumes in arteries and capillaries
Laminar and Turbulent Flow
                 Laminar flow
                     Streamlined
                     Outermost layer
                      moving slowest and
                      center moving fastest
                 Turbulent flow
                     Interrupted
                     Rate of flow exceeds
                      critical velocity
                     Fluid passes a
                      constriction, sharp turn,
                      rough surface
Aging of the Arteries

                Arteriosclerosis
                    General term for
                     degeneration changes in
                     arteries making them
                     less elastic
                Atherosclerosis
                    Deposition of plaque
                     on walls
        Capillary Exchange and
        Interstitial Fluid Volume
               Regulation
   Blood pressure, capillary permeability, and
    osmosis affect movement of fluid from
    capillaries
   A net movement of fluid occurs from blood into
    tissues. Fluid gained by tissues is removed by
    lymphatic system.
Fluid Exchange Across
    Capillary Walls
    Vein Characteristics and
    Effect of Gravity on Blood
             Pressure
Vein Characteristics       Effect of Gravity
 Venous return to heart    In a standing position,
  increases due to           hydrostatic pressure
  increase in blood          caused by gravity
  volume, venous tone,       increases blood
  and arteriole dilation     pressure below the
                             heart and decreases
                             pressure above the
                             heart
        Control of Blood Flow by
                 Tissues
   Local control
       In most tissues, blood flow is proportional to
        metabolic needs of tissues
   Nervous System
       Responsible for routing blood flow and
        maintaining blood pressure
   Hormonal Control
       Sympathetic action potentials stimulate
        epinephrine and norepinephrine
           Local Control of Blood Flow
                   by Tissues




   Blood flow can increase 7-8 times as a result of vasodilation of
    metarterioles and precapillary sphincters in response to increased
    rate of metabolism
       Vasodilator substances produced as metabolism increases
       Vasomotion is periodic contraction and relaxation of precapillary
        sphincters
Nervous Regulation of
   Blood Vessels
        Short-Term Regulation of
             Blood Pressure
   Baroreceptor reflexes
       Change peripheral resistance, heart rate, and stroke
        volume in response to changes in blood pressure
   Chemoreceptor reflexes
       Sensory receptors sensitive to oxygen, carbon dioxide,
        and pH levels of blood
   Central nervous system ischemic response
       Results from high carbon dioxide or low pH levels in
        medulla and increases peripheral resistance
Baroreceptor Reflex Control
Local mechanisms affect MAP:
Effects of pH and Gases
         Long-Term Regulation
           of Blood Pressure
   Renin-angiotensin-aldosterone mechanism
   Vasopressin (ADH) mechanism
   Atrial natriuretic mechanism
   Fluid shift mechanism
   Stress-relaxation response
General control of MAP:
Renin-Angiotensin-Aldosterone
        Mechanism
Vasopressin (ADH)
   Mechanism
          Long Term Mechanisms
         Which Lower Blood Volume
                                       Fluid shift
   Atrial natriuretic factor              Movement of fluid
       Hormone released from               from interstitial spaces
        cardiac muscle cells when           into capillaries in
        atrial blood pressure               response to decrease in
        increases, simulating an            blood pressure to
        increase in urinary                 maintain blood volume
        production, causing a          Stress-relaxation
        decrease in blood volume           Adjustment of blood
        and blood pressure                  vessel smooth muscle to
                                            respond to change in
                                            blood volume
Chemoreceptor Reflex Control
                             Shock
   Inadequate blood flow throughout body
   Three stages
       Compensated: Blood pressure decreases only a moderate
        amount and mechanisms able to reestablish normal blood
        pressure and flow
       Progressive: Compensatory mechanisms inadequate and
        positive feedback cycle develops; cycle proceeds to next stage
        or medical treatment reestablishes adequate blood flow to
        tissues
       Irreversible: Leads to death, regardless of medical treatment
Fetal circulation:

								
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