Blood Flow and Blood Pressure

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					Blood Flow and Blood

Dr. Jena Hamra
            Blood Vessels
 Components
  Fibrous connective tissue
  Smooth muscle
  Elastic connective tissue
     Type of epithelium

     Important in regulating blood pressure,
      vessel growth and absorption
 Proportion of components varies among
 different vessels
    Vascular Smooth Muscle
 Smooth  muscle of blood vessels
 Arranged in circular or spiral layers
 Responsible for vasoconstriction and
 Has muscle tone
   Modulated by
      Neurotransmitters
      Hormones

      Paracrines
     Arteries and Arterioles
 Smooth     muscle with elastic and fibrous
 Pattern of blood flow
   Arteries  Arterioles  Metarterioles 
 Arterioles
   Less elastic
 Metarterioles
   Blood can go to capillaries or venous
        Allows WBCs to go directly to venules
 Smallest  vessels
 Lack smooth muscle, elastic and fibrous
 Leaky junctions between cells
   Permeability of capillaries determined by
 Where exchange of oxygen, nutrients and
  wastes takes place
          Venules and Veins
 Venules
  Convergent flow pattern
  Smooth muscle in larger venules
 Veins
  Larger diameter than arteries
  Hold more that half of circulating blood
  Thinner walls
  Less elastic
     Expand easily
 Development of new blood vessels
   Children: normal development
   Adults: wound healing
   Endurance training
 Control of:
   Growth factors:
        Vascular endothelial growth factor
        Fibroblast growth factor

        Produced by smooth muscles or pericytes

     Antiangiogenic cytokines:
        Angiostatin

        Endostatin
              Blood Pressure
 Created byventricular contraction
  Sustained by elastic recoil of arteries
        Pushes blood forward
 Highest in arteries, lowest in veins
 Highest pressure is in aorta
  Highest during ventricular systole
        Systolic pressure
  Lowest during ventricular diastole
     Diastolic pressure
             Blood Pressure
 Pulse
    Rapid pressure increase when ventricles push
     blood into aorta
    Decreases over distance
 Pulse pressure
    Measure of amplitude of pulse pressure wave
    Pulse pressure = systolic pressure – diastolic
 Venous pressure
    Low
    One-way valves prevent backward flow
     Arterial Blood Pressure
 Pulsatile
 Mean arterial pressure (MAP)
  MAP = Diastolic P + 1/3 (Systolic P-
   Diastolic P)
 Measured by sphygmomanometry
  Increase pressure with cuff until greater
   than BP
      Sound heard when blood flows past
      First sound: systolic pressure

      Sound disappears: diastolic pressure
    Mean Arterial Pressure
 Major determinant of blood flow
 Function of:
  Cardiac output
       Flow into arteries
  Peripheral resistance
     Arterioles

     Flow out of arteries

  Balance of flow in and flow out
  Total blood volume
  Distribution of systemic blood
 Blood Volume and Blood Pressure
 Blood volume   affects blood pressure
  Blood volume increases  blood
    pressure increases
  Decreased blood volume  decreased
    blood pressure
 Compensatory mechanisms
        Vasoconstriction
     Water conservation
 Arterioles main     source of vascular
   Smooth muscle in walls
 Control of arteriolar resistance
   Myogenic autoregulation
        Vascular smooth muscle autoregulates
         degree of contraction
          • Degree of stretch
 Control ofarteriolar resistance
        Vasodilators
          • Nitric oxide, H+, K+, CO2,
            Prostaglandins, Histamine, pO2
        Change with state of metabolic activity
          • Active hyperemia
          • Reactive hyperemia
 Reflex Control of Vascular Smooth

 Sympathetic input
  Tonic input maintains myogenic tone
     Norepinephrine

         • Alpha receptors = Vasoconstriction
       Epinephrine
         • Alpha receptors = vasoconstriction
         • Beta-2 receptors = vasodilatation
            • Heart, liver, skeletal muscle
           Blood Distribution
 Dependenton metabolic needs
  Governed by:
     Number of vessels supplying organ/tissue
     Blood flow

         • Resistance
       Local and reflex control
              Capillary Exchange
 Exchange function of:
   Thin walls and pores of capillaries
      Allow movement of gases, water, dissolved
      Move by passive diffusion

 Types of capillaries
   Continuous
          Muscle, connective tissues, neural tissue
        Tight junctions
     Fenestrated
        Large pores

        Associated with absorptive epithelia
       Capillary Exchange
 Mechanisms:
  Passive diffusion
     Concentration gradient

     Proteins and other large molecules

  Bulk flow
     Mass movement of water and dissolved
      solutes between blood and ECF
        • Filtration
        • Absorption
       Regulation of Bulk Flow
   Hydrostatic Pressure
     Decreases as travel down capillary
     Forces water out of capillary
          Pores
   Osmotic Pressure
     Due to solute differences
          Plasma proteins
     Water moves into capillaries
     Constant all along capillary
   Net flow
     Determined by difference between hydrostatic
      and osmotic pressure
 Net filtration at arterial end.
Net absorption at venous end.
        Lymphatic System
 Function:
  Return filtered fluids and proteins to
     circulatory system
   Transfer fat from small intestine to
     circulatory system
   Trap pathogens for immune system
 One way movement of ECF from tissues
  to circulatory system
   Lymph capillaries lie close to blood
   Lymph vessel walls thin
 Lymph vessels
   Anchored to surrounding connective tissue
   Large gaps allow bulk flow
   Fluid inside = lymph
 Lymph flow dependent on:
   Contractile fibers in endothelial cells
   Smooth muscle in walls
   One-way valves
   External compression
         Skeletal muscles
 Causes
  Inadequate drainage of lymph
     Obstruction of lymph flow

  Capillary filtration > capillary
     Increase in capillary hydrostatic pressure
        • Increased venous pressure
     Decrease in plasma protein concentration

     Increase in interstitial proteins (ECF)
    Regulation of Blood Pressure
   Brain
     Medullary cardiovascular control center
     Modulation by:
        Hypothalamus
        Cerebral cortex

   Systemic
      Baroreceptors
        Stretch sensitive mechanoreceptors
        Monitor blood pressure

        Baroreceptor reflex

     Arterial chemoreceptors
        Low blood O2
    Orthostatic Hypotension
 Decrease in blood pressure upon standing
 Triggers baroreceptor reflex
  Decreased baroreceptor firing
  Signal to CVCC
  Decreased parasympathetic, increased
    sympathetic activity
  Results in increased blood pressure
  Skeletal muscle pump helps
       Cardiovascular Disease
   Coronary artery disease
     Atherosclerosis
          Coronary arteries blocked with cholesterol and Ca++
     Mechanism
        Macrophages ingest LDL-cholesterol

           • Form fatty streaks under endothelial lining
        Macrophage paracrines attract smooth muscle cell

           • Form “plaques”
        Unstable plaques rupture and trigger formation of
         blood clots
           • Blocks flow of blood to heart
        Role of Cholesterol
 Cholesterol not soluble in plasma
 Cholesterol carrier proteins
   High density lipoprotein (HDL)
   Low density lipoprotein (LDL)
 High LDL levels associated with heart
   Excess LDL moves into arterial walls
   Ingested by macrophages
 Chronically elevated blood
 Primary hypertension (>90%)
  No clear cause
        Increased peripheral resistance
  Adaptation of baroreceptors
  Contributes to atherosclerosis
  Can lead to congestive heart failure
     Ca++ channel blockers

     Beta blockers

     ACE inhibitors

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