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					   Blood Vessels-Chps. 14-19
Powered by the pumping action of the heart
  Heart
  Arteries-
             Elastic
             muscular
  Arterioles
  Capillaries
  Venules
  veins



 • Transporting nutrients and oxygen to the tissues
 • Transporting waste products away from the tissues
 • Transporting hormones
                        Lecture outline
I. Review anatomy of vessels                III. Getting to know “Flow” better
    A. Arteries                                  A. Velocity
    B. Elastic                                   B. Control of flow
    C. Muscular                                        i. Autoregulation
    D. Arterioles- resistance vessels                  ii. Nervous system
    E. Capillaries- exchange vessels                   iii. Endocrine-kidney (unit 4)
    F. Veins- capacitance vessels
                                            IV. Exchange of extracellular fluid- the
II. Ohm’s law is flow = change in               microcirculation
    pressure/ resistance                        A. Starling Forces
    A. Blood Flow                                   i. Capillary hydrostatic pressure
          i. Laminar vs. turbulent                  ii. Interstitial hydrostatic pressure
    B. Pressure- blood pressure                     iii. Capillary colloid osmotic
          i. Mean arterial pressure (MAP)           pressure
          ii. Central venous pressure               iv. Interstitial colloid osmotic
          iii. Pulse pressure                       pressure
    C. Resistance                               B. Lymphatic drainage
          i. Factors of resistance-             C. Causes of edema
    Poiseuille’s law


                                                                                        2
• Branch and diverge
• Blood away from heart
• Walls have 3 tunics
                                   Arteries
   – Tunica intima-simple
     squamous endothelium

   – Tunica media-circular
     sheets of smooth muscle
     (vasodilation and
     vasoconstriction- diameter
     controlled by local factors
     and sympathetic NS)

   – Tunica adventitia-
     connective tissue with
     collagen and elastin in
     longitudinal arrangement



                                              3
                            Arteries
• Elastic- largest arteries near
  heart
   – Low resistance
   – More elastin interspersed with
     the tunica media
   – Can distend and recoil back
     to pump blood (maintain
     blood pressure)
• Muscular-
   – Supply organs
   – Can regulate diameter of
     artery to control blood supply
     to organ
   – Thick tunica media with more
     smooth muscle
   – External and internal elastic
     lamina.

                                       4
       Arterioles
• Smallest arteries-
  “resistance arteries”
• THICK tunica media- little
  compliance
• Diameter controlled by
  local factors (intrinsic) and
  sympathetic division
  (extrinsic) and long-term
  factors (hormones)
• Metarterioles- just
  upstream of capillary beds.
• Precapillary sphincters-
  controls blood reaching
  capillary bed.                  5
      Capillaries
• Smallest blood vessels
• Single layer of endothelial
  cells and basal lamina
• Renew interstitial fluid- pick
  up wastes, drop off nutrients,
  etc.
• Most cells only 20-30 µm
  away
• Over 10 billion of them.




                                   6
    Types of Capillaries
•    Continuous
      – Most common and least
        permeable
      – Intercellular clefts and
        transcellular cytosis allows for
        exchange of molecules
      – Abundant in skin and muscle
•    Fenestrated
      – “Holes” in the endothelial
        membrane
      – Found in kidney
•    Sinusoidal/ discontinuous
      – Most permeable and least
        common
      – Big ‘holes” in endothelial
        membranes
      – Big clefts between cells
      – Liver, spleen, and bone marrow
                                           7
        especially
        • Volume reservoir- “capacitance vessels” (60-70%)
          of blood
Veins   • Have vasomotor control.
        • Valves in abdominal veins prevent backflow
        • Skeletal muscle “pump” and respiratory pump




                                                       9
  Vascular Distensibility= is the fractional increase in
  volume for each mmHg rise in pressure times original volume- veins are
  8x more distensible

                       0 mmHg                              100 mmHg


     Artery                                                     100 ml




       Vein                                                800 ml



In hemodynamics, it’s more valuable to know the total quantity of blood that can be
stored in a given portion of the circulation for each mmHg pressure rise.
Capacitance = increase in volume/increase in pressure                              10
The capacitance of veins is 24 times that of arteries.
                     Ohm’s Law
• Q=P/R
• Flow (Q) through a blood
  vessel is determined by:
• 1) The pressure
  difference (P) between
  the two ends of the
  vessel
   – Directly related to flow
• 2) Resistance (R) of the
  vessel
   – Inversely related to flow

• Can you rearrange the
  equation above and solve
  for P? Solve for R?            11
                Blood Flow (L/min)
• Blood flow is the quantity of
  blood that passes a given
  point in the circulation in a
  given period of time.
• Unit of blood flow is usually
  expressed as milliliters (ml) or
  Liters (L) per minute.
• Overall flow in the circulation
  of an adult is 5 liters/min
  which is the cardiac output.
• CO= HR X SV
• 70 b/min x 70 ml/beat
  =4900ml/min                        12
   Characteristics of Blood
           Flow
• Blood usually flows in streamlines with each layer
  of blood remaining the same distance from the
  wall, this type of flow is called laminar flow.
   – When laminar flow occurs, the velocity of blood in
     the center of the vessel is greater than that toward
     the outer edge creating a parabolic profile.
                                               Laminar flow




                                                            13
                  Blood Vessel
      Laminar Vs. Turbulent Blood Flow
                  Causes of turbulent blood flow:
                     • high velocities
                     • sharp turns in the circulation
                     • rough surfaces in the circulation
                     • rapid narrowing of blood vessels


Turbulent flow




• Laminar flow is silent, whereas turbulent flow tend to cause murmurs.
• Murmurs or bruits are important in diagnosing vessels stenosis, vessel shunts, and
cardiac valvular lesions.
                                                                                 14
Effect of Wall Stress on Blood Vessels
Turbulent flow increases resistance and wall stress
Nitric oxide released by endothelial cells to reduce the stress




                                                          15
Aortic Aneurysm                      Atherosclerosis
  Blood Pressure—
  The driving force               Stephen Hales
                                  1733
• Blood pressure (hydrostatic
  pressure) is the force
  exerted by the blood against
  any unit area of vessel wall.
• Measured in millimeters of
  mercury (mmHg). A pressure
  of 100 mmHg means the
  force of blood was sufficient
  to push a column of mercury
  100mm high.
• All vessels have it – but
  we’re usually addressing
  arteries when we refer to it.
                                           16
               Ejected Blood

contracted


             When the LV contracts more blood enters the
             arterial system than gets pushed onward.
             This causes the arteries to stretch and
             pressure within them to rise. The highest
             pressure achieved is known as the systolic
             pressure.
                                                       17
                         Recoil of the elastic artery
relaxed


          As the LV relaxes, the stretched arterial walls recoil
          and push the contained blood onward through the
          system. As they recoil, the amount of blood
          contained decreases as does pressure. The lowest
          pressure achieved just before the next contraction is
          the diastolic pressure.
                                                               18
    Mean Arterial Pressure (MAP)
 FLOW = arterial - venous pressure (P)   100 mmHg
                     resistance (R)

• Is an average, but not a simple
                                                       A
  arithmetic average                        0 mmHg
• Heart spends longer in diastole              R = .1mmHg/ml/min
  than systole
                                           FLOW = 1000 ml/min
• Value is significant- why?
• The difference between the mean
  arterial pressure and the pressure       100 mmHg
  in the venous system drives the
  blood through the capillary beds.                       B
• MAP= .4 (systolic) + .6 (diastolic)=    20 mmHg
  96mmHg                                        R = .1mmHg/ml/min
• Venous pressure is about 2mmHg
                                          FLOW = 800 ml/min   19
            Central Venous Pressure
•   Pressure in the right atrium is called
    central venous pressure.
•   determined by the balance of the heart
    pumping blood out of the right atrium
    and flow of blood from the large veins
    into the right atrium.
•   normally 0 mmHg, but can be as high as
    20-30 mmHg.
•   More vigorous heart contraction (lower
    CVP).
•    Less heart contraction (higher CVP)
•   Factors that increase CVP:
    -    increased blood volume
    -    increased venous tone (peripheral
    pressure)
    -    dilation of arterioles                 Figure 15-9; Guyton and Hall
    -    decreased right ventricular function
    -    Skeletal and respiratory pumps

                                                                               20
Arterial Pulsations and Pulse Pressure
• The height of the pressure pulse is the
  systolic pressure (120mmHg), while the
  lowest point is the diastolic pressure
  (80mmHg).
• The difference between systolic and diastolic
  pressure is called the pulse pressure
  (40mmHg). Systolic Pressure


                               }    Pulse Pressure

                                                     21
                   Diastolic Pressure
Factors Affecting Pulse Pressure
• Stroke volume —increases in
stroke volume increase pulse
pressure, conversely decreases
in stroke volume decrease
pulse pressure.

• Arterial compliance —decreases in
compliance increases pulse
pressure; increases in compliance     Figure 15-5; Guyton and Hall
decrease pulse pressure.


                                                                     22
             Stroke
             volume

                                                  Stroke
  Cardiac                                         volume
  output              Systolic Pressure

         Mean
         Pressure                            }
                                             Pulse Pressure


                      Diastolic                   Arterial
Total                 Pressure        Time       compliance
Peripheral
resistance

             HR x SV = CO = MAP/ TPR
             MAP= (0.4 SP) + (0.6 DP)
             PP= SP- DP                                23
   Damping of Pulse                         What’s an anatomical reason for
   Pressures in the                         why the pressure fluctuation
                                            disappears here?
   Peripheral Arteries
• The intensity of pulsations
becomes progressively less in the
smaller arteries.
• The degree of damping is
proportional to the resistance of
small vessels and arterioles and the
compliance of the larger vessels.
•Elastic arteries:
     • large radii, low resistance, some
     pressure reservoir
•Muscular arteries
     •Smaller radii
     •Little more resistance
     •More pressure reservoir
•Arterioles
     •Thick tunica media vs. radius        Figure 15-6; Guyton and Hall   24
    •major pressure reservoir
Blood Pressure Profile in the Circulatory
               System
            120




                                                                                   Pulmonary arteries
            100




                                                                                                                      Pulmonary veins
 Pressure
 (mmHg)



             80




                                                                   Large veins
                                                     Small veins
                             Capillaries




                                                                                                        Capillaries
                                           Venules
             60
             40
             20
              0
                      Systemic                                                   Pulmonary
Circulatory pressure- averages 100mmHg
    Arterial blood pressure-100-35mmHg
    Capillary pressure- 35mmHg at beginning and 10-15mmHg at end
    Venous pressure-15-0mmHg
•Large pressure drop across the arteriolar-capillary junction                                                                           25
                                                     R = ΔP = mmHg
                         Resistance                       Q ml/min

• Resistance is the impediment
  to blood flow in a vessel.
• Can not be measured directly

How Would a Decrease in Vascular Resistance Affect
Blood Flow?


     FLOW =               P
                     RESISTANCE
                              FLOW =                P
Conversely,
                                               RESISTANCE
   Therefore, flow and resistance are inversely related!             26
    Resistance makes a difference for the two
               sides of the heart!
• Let’s say the CO (flow) is roughly          100 mmHg
  100ml/sec (easier math).
• To calculate systemic resistance vs.
  pulmonary resistance we need to              16
  know pressure differences.                   mmHg
• Pulmonary resistance is 16-2/100                    2mmHg
• Systemic resistance is 100/100
• So, CO is same on each side of         0mmHg
  heart (has to be!), but right side
  generates less pressure due to lower
  resistance (1/7th than systemic).


                                         R = ΔP = mmHg
                                              Q ml/min
                                                              27
                Factors of Resistance


      Poiseuille’s Law =   Q =_Pr4
                               8l
   • Blood viscosity
   • Total vessel length
   • Vessel diameter
• Resistance 
  (length)(viscosity)
    (radius)4

                                        28
      Viscosity
• What are the major
  contributors to blood
  viscosity?
• As viscosity                                    Figure 14-11; Guyton and Hall
  increases, resistance
  will…
• An increase in plasma
  EPO will cause
  resistance to…

                          Figure 14-12; Guyton and Hall
                                                                                  29
       Total Vessel Length
• Longer the vessel.....more
  opportunity for resistance.


         Radius




                                30
               So, lets review:
      Blood Flow is volume flowing/time
     • Ohm’s Law                                        • Increase pressure-
     • Blood Flow (Q) = Δ P/ R                            increase blood flow
                                                        • Decrease
             Blood flow in center is fastest-
             because that is the area of least
                                                          resistance-
             resistance                                   increase blood flow
                                                        • Increase
                                                          resistance-
P1                                               P2
                                                          decrease blood
                                                          flow
                                                              –   Vessel diameter
                          ΔP= P1-P2                           –   Viscosity
                                                              –   length
                                                              –   Turbulence (usually
•    As resistance decreases, flow will…                          result of an occlusion
•    As the pressure gradient increases, flow will…               reducing vessel
                                                                  diameter unevenly)
•    Which does the heart influence more: pressure gradient
     or resistance?                                                                    31
Flow (amount of blood/time) MUST
  be the same through vessels in
             series!
 If a pipe’s diameter changes over its length, a fluid will flow through
 narrower segments faster than it flows through wider segments
 because the volume of flow per second must be constant throughout
 the entire pipe.

 Flow (volume/time) vs. velocity (distance/time) are NOT synonyms!




                                                                     32
     If capillaries have such a small diameter,
     why is the velocity of blood flow so slow?
     Aorta >Arterioles > Small veins >Capillaries




We need slow blood flow in the capillaries—the exchange vessels   33
     Control of blood flow through
    vessels- Why is this important?
• Perfusion vs. ischemia vs.
  hypoxia vs. anoxia vs.
  infarction
• Tissue Perfusion
  Dependent on:
   – Cardiac output
   – Peripheral resistance
   – Blood pressure
• Regulation of perfusion
  dependent on:
   – Autoregulation (Acute, local,
     intrinsic)                      http://www.flometrics.com/services/artery/
   – Neural mechanisms (acute)
   – Endocrine mechanisms (long-
     term)


                                                                          34
 Autoregulation  the automatic adjustment of blood flow to
  each tissue in proportion to the tissue’s requirements at any
     instant even over a wide range of arterial pressures
   Working          Tissue temp. rises
   Muscle                                          Arterioles
    Tissue          Tissue CO2 levels rise       serving tissue
active hyperemia:
                                                 vasodilate and
   when tissues     Tissue O2 levels fall         precapillary
 become active,
    blood flow
                                                sphincters relax
                    Lactic acid levels rise
    increases.
Aka: intrinsic
metabolic                                      Increased blood
vasodilation                                    flow to tissue
                        CO2 removed
  Now arterioles
  will                  Lactic acid removed
  vasoconstrict
  and
  precapillary                  Heat removed   O2 delivered
  sphincters                                                       35
  contract
Autoregulation of Blood Flow to specific
                tissues
                       • Vasodilator agents
                            Histamine
                            Nitric oxide
                            Elevated temperatures
                            Potassium/hydrogen ions
                            Lactic acid
                            Carbon dioxide
                            Adenosine/ ADP
                       • Vasoconstrictors
                            Norepinephrine and
                              epinephrine
                            Angiotensin
                            Vasopressin (ADH)
                            Thromboxane


                                                 36
Other ways to ultimately change blood flow throughout the body is to change
Pressure and Resistance
 Arterial Pressure = Cardiac Output x Total Peripheral Resistance




                                         Short term BP control- nervous

                                                                   37
                                       Long Term BP control- hormonal
     Brain Centers involved in Short
            Term BP Control
• Vasomotor
   – Adjusts peripheral
     resistance by adjusting
     sympathetic output to the
     arterioles


• Cardioinhibitory- transmits
  signals via vagus nerve to
  heart to decrease heart rate.
  (parasympathetic)
• Cardioacceleratory/
  contractility-sympathetic
  output                               38
    Vasomotor control: Sympathetic Innervation
                of Blood Vessels
• Sympathetic nerve fibers
  innervate all vessels except
  capillaries and precapillary
  sphincters (precapillary
   sphincters follow local control)
• Innervation of small arteries
  and arterioles allow                Figure 18-2; Guyton and Hall

  sympathetic nerves to increase
  vascular resistance.
• Large veins and the heart are
  also sympathetically innervated.



                                                                     39
     Anatomy of the Baroreceptors
• spray type nerve endings located in
  the walls of the carotid bifurcation
  called the carotid sinus and in the
  walls of the aortic arch-
  pressoreceptors that respond to
  stretch.
• Signals from the carotid sinus are
  transmitted by the glossopharyngeal
  nerves .
• Signals from the arch of the aorta are
  transmitted through the vagus into the
  NTS.
• Important in short term
  regulation of arterial pressure.
   – They are unimportant in long term
     control of arterial pressure because
     the baroreceptors adapt.
                                                                           40
                                            Figure 18-5; Guyton and Hall
       Response of the Baroreceptors to
              Arterial Pressure                                            Figure 18-7; Guyton and Hall



     Constrict                        Pressure at
  Common Carotids                   Carotid Sinuses



                                       Arterial Pressure




                                         •   Baroreceptors respond to changes in arterial
                                             pressure.

                     Constrictors        •   As pressure increases the number of impulses
                                             from carotid sinus increases which results in:
                                              1) inhibition of the vasoconstrictor
                                              2) activation of the vagal center
                                                                                                    41
Figure 18-5; Guyton and Hall
 Functions of the Baroreceptors
• Maintains relatively constant pressure despite
  changes in body posture.


                                           Decrease
 Supine               Standing           Venous return

       Sympathetic
      Nervous Activity
                                             Decrease
          Vasomotor                       Cardiac Output
           Center

                          Sensed By
                         Baroreceptors       Decrease
                                         Arterial Pressure   42
 BP rises
                       Decreased           Decreased NE
                                                                Vasodilation
                       vasomotor           release on
                       activity            arterioles
Detected by
baroreceptors in
aortic arch &
carotid sinus                                                          Decreased PR



Info sent to cardiac   Increased                 Increased vagus
                       cardioinhibitory                                    Decreased
and vasomotor                                    activity
                       activity                                            BP
centers

                                                 Increased ACh
                                                 release on heart

 Decreased                                                              Decreased CO
 cardioacceleratory     Decreased NE             Decreased SV
 activity               release on heart         and HR
               Carotid and Aortic
               Chemoreceptors
• Chemoreceptors are chemosensitive
  cells sensitive to oxygen lack, CO2
  excess, or H ion excess.
• Chemoreceptors are located in carotid
  bodies near the carotid bifurcation and
  on the arch of the aorta.
• Activation of chemosensitive receptors
  results in excitation of the vasomotor
  center.

                                            Figure 18-5; Guyton and Hall
   O2
   CO2                                         Sympathetic
             Chemoreceptors      VMC                                       BP
                                                activity
   pH                                                                      44
Nervous control also found in the heart-
          Bainbridge Reflex
• Prevents damming of blood in veins, atria and
  pulmonary circulation.
• Increase in atrial pressure increases heart
  rate.
• Stretch of atria sends signals to VMC via
  vagal afferents to increase heart rate and
  contractility.
Atrial     Vagal      Vasomotor           Heart rate
Stretch   afferents    Center             Contractility

                                                     45
The Microcirculation-chapter
                      16 of nutrients to
• Important in the transport
  tissues.
• Site of waste product removal.
• Over 10 billion capillaries with surface
  area of 500-700 square meters perform
  function of solute and fluid exchange.




                                        Figure 16-1;
                                        Guyton and Hall   46
  Most substances are
  exchanged via diffusion



Concentration
differences
across capillary
enhances
diffusion.                  47
        Determinants of Net Fluid Movement across
               Capillaries-Starling forces




       Figure 16-5; Guyton and Hall


• Capillary hydrostatic pressure (Pc)-tends to force fluid
  outward through the capillary membrane.
(30 mmHg arterial; 10mmHg venous- average 17.3mmHg)
• Interstitial fluid hydrostatic pressure (Pif)- opposes filtration
  when value is positive (but it’s not positive-- due to
  lymphatic drainage! – 3mmHg).
                                                                 48
     Determinants of Net Fluid Movement across
            Capillaries-Starling forces




      Figure 16-5; Guyton and Hall

• Plasma colloid osmotic pressure ( c)- opposes filtration
  causing osmosis of water inward through the membrane
    – Colloid osmotic pressure of the blood plasma. (28mmHg)
    – 75% from albumin; 25% from globulins
• Interstitial fluid colloid pressure ( if) promotes filtration by
  causing osmosis of fluid outward through the membrane
    – Colloid osmotic pressure of the interstitial fluid. (8mmHg)
    – 3gm%
                                                                      49
     Net Forces in Capillaries
Filtration= Kf X (Pc- Pif - c + if)                                 mmHg
 Mean forces tending to move fluid outward:
   Mean Capillary pressure                                           17.3
 Negative interstitial free fluid pressure                            3.0
   Interstitial fluid colloid osmotic pressure                        8.0
 TOTAL OUTWARD FORCE                                                 28.3
 Mean force tending to move fluid inward:
   Plasma colloid osmotic pressure                                   28.0
 TOTAL INWARD FORCE                                                  28.0
 Summation of mean forces:
   Outward                                                           28.3
   Inward                                                            28.0
 NET OUTWARD FORCE                                                    0.3
   Net filtration pressure of .3 mmHg which causes a net filtration rate of
   2ml/min for entire body (2-4 liters/day!)                                  50
If capillary BP is greater than capillary
OP, there will be net movement of fluid
out of the capillary.

                  Capillary BP

                Filtration
                                                                              Capillary OP
     Pressure




                                                                   Reabsorption



                     If capillary BP is less than capillary OP, there will be net movement of
                     fluid into the capillary.


                Arterial end                                              Venous end
                                Distance along the capillary

   Filtration= Kf X (Pc- Pif - c + if)
• Lymphatic vessels collect        2ml/min Excess
  lymph from loose connective      tissue fluid is
  tissue
   – Fluid flows only toward the   returned to the
     heart                         blood vessels via the
   – Collect excess tissue fluid   lymphatic system!
     and blood proteins and
     carry to great veins in the
     neck
   – All three tunics
   – NO pump!
   – Valves!
• contains plasma, water,
  ions, sugars, proteins,
  gases, amino acids- is
  colorless, but low in protein
  compared to blood
• Lymph can contain
  hormones, bacteria, viruses,
  cellular debris, traveling                               52
  cancer cells, macrophages
    Causes of Edema
 • Excessive accumulation of tissue
   fluid.
 • Edema may result from:
     – High arterial blood pressure.
     – Venous obstruction.
     – Leakage of plasma proteins
        into interstitial fluid.
     – Valve problems
     – Cardiac failure
     – Decreased plasma protein.
     – Obstruction of lymphatic
        drainage. Elephantiasis-
        Wuchereria bancrofli


I would see your homework packet and study page 303 of Guyton and Hall!   53
Unbalanced Ventricular Output




                                54
Unbalanced Ventricular Output




                                55
                                                    ISF
   Hypertension         capillary BP            formation

Starvation


  Lack of             in          capillary               ISF
  dietary          plasma             OP                 formation
  protein          albumin


 Histamine         Vasodilation          capillary BP



      capillary                        ISF
    permeability                     formation                  56
Burn/crush            capillary                        ISF
  injury            permeability          Cap OP
                                                     formation




      Backup of blood in            pulmonary        ISF
      pulmonary circuit            capillary BP    formation


L. Ventricle
   failure



        Decreased blood
                                      systemic        ISF
        flow in systemic                            formation
                                    capillary BP
             circuit                                       57

				
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