Chapter 21 The Cardiovascular System Blood Vessels by kellena97

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									Chapter 21:

The Cardiovascular System:
Blood Vessels
Vessel Structure - General
 All vessels same basic
   structure
 3 wall layers (or tunics)
      Tunica adventitia (externa)
       - elastic and laminar fibers
      Tunica media
        thickest layer
        elastic fibers and smooth
         muscle fibers
      Tunica interna (intima)
          endothelium – non-stick
           layer
          basement membrane
          internal elastic lamina
 Lumen - opening
 Structure/function
   relationship changes
   as move through
   cardiovascular tree

 Tunic thickness and
   composition variable
   throughout
   cardiovascular tree
Vessel Structure – Elastic Arteries
                         Elastic
                          (conducting)
                          arteries
                           Near heart
                           Thick walls
                           More elastic
                             fiber, less smooth
                             muscle
                           Lose elasticity
                             with aging
Vessel Structure - Elastic Arteries
                      Aorta and elastic
                       arteries
                        Can vasoconstrict or
                          vasodilate
                        Large arteries expand,
                          absorb pressure wave
                          then release it with
                          elastic recoil -
                          Windkessel effect
                        Help to push blood along
                          during diastole
                        With aging have less
                          expansion and recoil
Vessel Structure – Muscular Arteries
                         Muscular
                          (distributing)
                          arteries
                           Deliver blood to
                             organs
                           More smooth
                             muscle
                           Less elastic
                             fibers
Vessel Structure - Arterioles
                         Arterioles
                              Distribution of
                               blood in organs
                              Composition varies
                               depending on
                               position - more
                               muscle, less
                               elasticity nearer
                               heart
                              Regulate flow from
                               arteries to
                               capillaries
                                  Flow = ΔP/R
                                  vary resistance
                                   by changing
                                   vessels size
                              Site of blood
                               pressure regulation
Vessel Structure - Capillaries
                      Microcirculation
                       connects arteries and
                       veins
                      Found in nearly every
                       tissue in body
                         Higher the metabolic
                           rate, more capillaries in
                           tissue
                         Muscle many caps
                           (>600/mm2)
                         Cartilage none
Vessel Structure - Capillaries




 Allow exchange of nutrients and wastes between blood
  and tissue
 Capillary structure - simple
    Basal lamina - connective tissue
    Endothelial cells
 Structure/function
Flow Regulation
                   Regulation by vessels with
                    smooth muscle
                     Metarterioles
                          connect arterioles to
                           venules through capillary
                           bed
                          allows flow through
                           capillary bed w/out flow
                           through caps
Flow Regulation
                   True capillaries
                     Pre-capillary sphincter
                        ring of smooth muscle
                        open/close to control
                         flow
                          regulated by chemicals
                     Intermittent vasomotion
                       – caps open for flow 5-
                       10X min
Types of Capillaries
                        3 types of capillaries

                          1.   Continuous capillaries
                                continuous endothelial
                                 cells except for cleft
                                 between cells
                                tight junctions between
                                 endothelial cells
                                 prevent most things
                                 from leaving caps
                                most capillaries in body
Types of Capillaries


                       2. Fenestrated capillaries
                           fenestrations (slits)
                            allow for filtration of
                            small substances
                           glomerular capillaries in
                            kidney
Types of Capillaries


                       3. Sinusoid capillaries
                           wider gaps between
                            endothelial cells
                            allowing RBC’s to exit
                            the caps
                           found in liver
Vessel Structure - Veins
                            Venules
                              Collect blood from
                                caps carry it to
                                veins
                              Structure changes
                                with position
                              Become more
                                vessel-like (walls)
                                as move from
                                capillaries
Vessel Structure – Veins
                            Veins
                              Interna thicker
                                than arteries
                              Media thinner, less
                                muscle
                              Externa thick
                              Valves
                              Pressure low
                              High compliance -
                                change volume
                                easily with small
                                change in pressure
                              Varicose veins
Vessel Structure - Histology
                  Very different morphology
                    under light microscopy
                  Tunica media thickness
                    differentiates artery from vein
Vein   Artery   Artery   Vein
Vessel Structure/Function
                        At rest
                            60% of blood located in
                             veins and venules
                            Serve as reservoirs for
                             blood, “storing” it until
                             needed
                            Particularly veins of
                             abdominal organs, skin
                        ANS regulates volume
                         distribution
                            Vasoconstrict
                            Vasodilate
                            Open areas of circulation
                             to be supplied with blood
                                veins at rest
                                caps during exercise
                            Can “shift” volumes to
                             other areas as needed
Vessel Structure/Function




                               0.75 L/min
   Rest




               CO = 5 L/min
Vessel Structure/Function

               CO = 25 L/min


 Heavy
 Exercise                         20 L/min




                                0.75 L/min
   Rest




               CO = 5 L/min
Physiology of Circulation
 Flow = ΔP/R
   or CO = MAP/R
   MAP - mean arterial pressure
   Higher pressure to lower pressure with resistance
     (R) factor
 Blood pressure
   Pressure of blood on vessel wall
   Measurement of pressure of a volume in a space
   Systole/diastole - 120/80
   BP falls progressively from aorta to O mm Hg at RA
Regulation of Blood Flow
 Resistance - opposition to blood flow from blood and
  vessel wall friction
 Factors that affect resistance (R)
   Viscosity - V R
      thickness of blood
     dehydration, polycythemia
   R proportional to vessel length
     garden hose vs. straw
     obesity
   Vessel diameter
     changes in diameter affect flow
            vessel wall drag – blood cells dragging against the wall
            laminar flow – layers of flow
        R inverse proportional to radius4
            decrease in r by 1/2 R 16X
            only important in vessels that can change their size actively
Regulation of Pressure, Resistance
                    Systemic vascular resistance
                      (Total Peripheral Resistance -
                      TPR)
                         All vascular resistance
                          offered by systemic vessels
                         Which vessels change size?
                         Resistance highest in
                          arterioles
                         Largest pressure drop occurs
                          in arterioles
                    Relationship of radius to
                      resistance in arterioles
                      important due to smooth
                      muscle in walls
Systemic Blood Pressure
 Arterial Blood Pressure
   Pulsatile in arteries due to
     pumping of heart
   Systolic/diastolic
   Pulse pressure = systolic
     (minus) diastolic
     Q - Windkessel effect on
        pulse pressure?
         A   - Decreases pulse
             pressure
     Q   - What is the effect of
         hardening of the arteries
         on pulse pressure?
         A   - Increases pulse
             pressure
Systemic Blood Pressure
                    Capillary Blood
                     Pressure
                      Relatively low blood
                          pressure
                      Low pressure good for
                          caps because:
                           caps are fragile - hi
                             pressure tears them
                             up
                           caps are very
                             permeable - hi
                             pressure forces a lot
                             of fluid out
Systemic Blood Pressure
                    Venous return
                      Volume of blood flowing
                          back to heart from
                          systemic veins
                      Depends on pressure
                          difference (ΔP) from
                          beginning of venules (16
                          mmHg) to heart (0
                          mmHg)
                      Any change in RA
                          pressure changes
                          venous return
 Help for venous return
   Skeletal muscle pump
      muscles squeeze veins
      force blood back to heart
        valves prevent back flow




   Respiratory pump
        inhaling pulls air into lungs
        helps to pull blood back into
         thorax
Velocity of Blood Flow
                     Velocity of blood flow -
                         inversely related to total
                         cross sectional area (CSA)
                         of vessels
                     Aorta
                            Total CSA 3-5 cm2
                            Velocity 40 cm/sec
                     Capillaries
                            Total CSA 4500-6000 cm2
                            Velocity 0.1 cm/sec
                     Vena Cava
                            Total CSA 14 cm2 in vena
                             cava
                            Velocity 5-20 cm/sec
Vessel Structure - Function
 Capillary Function
   Site of exchange between blood and tissues
   Delivery of nutrients and removal of wastes
   Slow flow allows time for exchange
 Mechanisms of nutrient exchange
   Diffusion - O2, CO2, glucose, AA's, hormones
    diffuse down [ ] gradients
   If lipid soluble, can travel through cell
   If water soluble, between cells
Capillary Fluid Exchange
                                        Fluid movement
                                           Fluid filtered and
                                             reabsorbed across
                                             capillary wall
                                           Starling’s law of the
                                             capillaries


 Forces driving the movement of fluid
    Hydrostatic pressure capillary (HPc)
    Hydrostatic pressure interstitial fluid (HPif)
    Osmotic pressure capillary(OPc)
    Osmotic pressure interstitial fluid (OPif)
 Net filtration pressure (NFP) is a sum of all
Capillary Fluid Exchange




 On average 85% of fluid filtered at arteriole end is
   reabsorbed at venular end
Maintaining Blood Pressure -
Short Term Mechanisms - CNS
 Neural Control - Cardiac centers in medulla
   Vasomotor center
     medullary area dedicated to control of blood vessels
     sends sympathetic output to blood vessels
              Vasoconstricts or vasodilates as needed
              tone - normal amount of vasoconstriction or vasodilation
              can vary tone which varies delivery of blood
          receives input from different sources
              baroreceptors
              chemoreceptors
Maintaining Blood
Pressure – Short term
mechanisms – CNS reflexes

 Baroreceptor initiated
  reflex
   Located at carotid sinus and
     aortic arch
   Monitor changes in blood
     pressure
   Regulate activity of
     Sympathetic Nervous
     System (vascular tone)
Maintaining Blood Pressure –       Short term
mechanisms – CNS reflexes
                             Chemoreceptor
                              initiated reflexes
                               Carotid bodies,
                                 aortic bodies
                               Monitors changes
                                 in chemicals (O2,
                                 CO2, [H+])
                                CO2,  H+,  O2
                                 (stresses) result in
                                  sympathetic
                                 activity and  BP
Maintaining Blood Pressure – Short
term mechanisms – CNS reflexes
 Influence of Higher Brain Centers (areas above
  medulla) - Cortex and Hypothalamus
   Not involved in minute to minute regulation
   Influence vasomotor center depending on conditions
       public speaking
       temperature regulation
Maintaining Blood Pressure -
Short Term Mechanisms - Hormones
                        Renin - Angiotensin -
                         Aldosterone
                          Renin
                             enzyme from kidney
                             results in formation of
                              Angiotensin II (AII)
                          AII
                             vasoconstrictor
                             stimulates ADH, thirst
                               stimulates aldosterone
                                - Na+ reabsorption
                          Why/how would these
                            things affect blood
                            pressure?
Maintaining Blood Pressure -
Short Term Mechanisms - Hormones
             Adrenal medulla - Epi and Norepi
                CO (HR,  SV)
               Constrict abdominal, cutaneous
                 arterioles/venules
               Dilate cardiac, skeletal muscle beds
             Why/how would this affect blood
              pressure?
Maintaining Blood Pressure -
Short Term Mechanisms - Hormones
                   Antidiuretic Hormone
                    (ADH)
                     Osmoreceptors in
                       hypothalamus
                     Retains fluid (inhibited by
                       alcohol)
                     Vasoconstriction at high
                       levels
                   Why/how would this affect
                    blood pressure?
Maintaining Blood Pressure -
Short Term Mechanisms - Hormones




 ANP (atrial natriuretic peptide)
   Released from atrial cells in response to BP
   Vasodilator, Na+ and water loss, opposes Aldosterone
 Why/how would this affect blood pressure?
Maintaining Blood Pressure -
Long Term Regulation
 Renal mechanism
   Volume in a space
   Regulate space in the
    short term – we just
    talked about it!
     nervous control
     hormones
   Regulate volume in the
    long term
   The kidneys!
      BP,  urine flow to 
       BP
      BP,  urine flow to 
       BP
Control of Blood Flow
 Autoregulation (local control) - local automatic
  adjustment of blood flow to match tissue
  needs
   Physical changes
        Warming -  vasodilation
        Cooling -  vasoconstriction
   Chemical changes - metabolic products
        Vasodilators
        Vasoconstrictors
 Myogenic control
   smooth muscle controls resistance
    stretch  contraction,  stretch  relaxation
Blood Flow in Special Areas
 Skeletal Muscle
   Wide variability in amount of flow
   Sympathetic regulation from brain in response to level of
    activity
     α receptors - vasoconstrict
     β receptors - vasodilate
   Metabolic regulation in tissue
     low O2  vasodilate to increase flow
     hi O2  vasoconstrict to decrease flow

 Brain
   Very little variability in flow
   Stores few nutrients so flow must be maintained!
   Metabolic regulation
Blood Flow in Special Areas
 Skin
   Supplies nutrients, aids in temperature regulation, provides
     a blood reservoir
   Metabolic and sympathetic regulation
 Lungs
   Low pressure (25/10), low resistance
   Flow regulated by O2 availability in the lungs
      hi O2  vasodilate to increase flow – opposite to muscle
      low O2  vasoconstrict to decrease flow – opposite to muscle

 Heart
   Variable flow depending on activity
   Metabolic and sympathetic regulation
Regulation of Blood Pressure




                        MAP MAP/R
                        CO = = CO x R

								
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