PNB Vasculature

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PNB Vasculature
2013-02-20 08:12:33
artery vein capillary radius

PNB 2265
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  1. arteriole function:
    • will capillary bed receive blood (carry blood to tissue)
    • determines MAP by effect on TPR
  2. Arteriole Myogenic tone
    spontaneous contraction of smooth muscle in tunica muscle.

    • contract smooth muscle more-->VASOCONSTRICTION
    • relax of smooth muscle-->VASODILATION
  3. smaller the radius....
    • GREATER the friction
    • BIG increase in flow
    • Friction-main factor in resistance (R)
    • R-inverseley proportional to radius (exponential) R=1/r4
    • -SMALL Decrease radius=BIG increase in resistance=BIG decreased flow=BIG increase pressure
    • -SMALL Increase radius=BIG decrease in resistance=BIG increase in flow=SMALL decrease in pressure
  5. Regulation of Arterioles
    • -local control 
    • -neural (reflex) contol
    • -Hormonal Control
  6. Intrinsic regulation of arterials
    • -local control, no nerves, no hormones
    • -Active Hyperemia: blood flow adjusted to meet tissue needs
    • -arterioles radius will increase if it needs more O2 from release of chemical signals
  7. Stimulus of Intrinsic local control of Arteriolar radius
    • -decreased O2
    • -increased CO2
    • -increased H+
    • -decreased pH
    • -metabolites (K+), increase osmolarity
  8. How does Intrinsic (local) control of arteriolar radius respond?
    increase Radius of arterioles, metarterioles and pre-capillary sphincters

    *make sure tissues get blood/O2 they need
  9. function of beta-2 receptors...
    EPI- beta2- relax and opens smooth muscle
  10. Flow Autoregulation..
    • local/intrinsic control of arteriolar radius
    • -decreased BP in organ-->arteriolar DILATION restores blood flow
  11. flow autoregulation is mediated by
    • several...
    • decreased O2
    • increased metabolites
  12. extrinsic control (reflex-NEAURAL/HORMONAL-control of arteriolar radius
    • -SYMP STIMULIS-release of NE, bind to alpha-receptors -->mass vasoconstriction of arterioles-->increased TPR-->increased MAP
    • -Sympathetic stimulus: adrenal medulla release EPI-->alpha-adrenergic receptors AND BETA2 RECEPTORS-->
    • EPI will cause vasodilation (in arterioles, most skeletal muscles, heart, lungs brain)

    -mass vasoconstriction-->inc. TPR-->inc MAP

    -parasympathetic stim-less important
  13. Angiotensin II
    strong vasoconstrictor
  14. Local controls are NOT important in.....
    MAP regulation
  15. NEURAL controls are important in....
    regulation of MAP
  16. During fight or flight, which control is more important? Why?
    NEURAL controls will override local to make sure we stay alive
  17. capillaries function:
    • -transport via difussion, (between blood and interstitial fluid)
    •        -lipid-soluble, ion polar molecules-    
    •           endothelial cell membrane
    •        -glucose: carrier mediated diffusion
    • -RBC squeeze through in single file, so volume decreases and more time for exchange

    *not leaky, carrier-mediated diffusion plays larger roles
  18. structre of capillaries
    ONE THIN capillary wall (tunica intima) and basement membrane
  19. Capillary beds
    • formed by capillarys
    • metarteriole: connects arteriole with venule, true capillarys branch off metarteriole-
  20. precapillary sphincter
    ultime control if blood enters capillary/tissue

    regulated by local/neural control
  21. Capillary BP at entrance
    35-40 mmHg
  22. capillary BP at end
    15-20 mmHg
  23. Velocity of Capillary blood
    • SLOW compared to rest of vascular system (due to so many capillaries), slows down rate of  flow
    • -slow rate of travel allows for COMPLETE EXCHANGE
  24. filtration
    fluid moving out of the capillary/blood
  25. reabsorption
    back to the blood (into capillary)
  26. 2 primary forces govern fluid movement in and out of capillary
    • hydrostatis pressure (capillary BP) force driving fluid out. (filtration) *plasma protein can not diffuse*
    • Colloid osmotic pressure of blood-caused by (reabsorbsorption)
    •    -caused by impenetrable non-plasma    
    •      penetrating proteins

    • filtration varies over time (beg-high, end-decrease)
    • absorption (remains constant due to colloid osmotic presure
  27. beginning/end of capillary (BP, OP, NPO)
    • Beginning:
    • Hydrostatic BP-INCREASE
    • colloid OP- DECREASE
    • Net filtration pressure (BP-CoP=NFP) MORE filtration

    • End:
    • BP: lower 
    • CoP: remains the same (BUT HIGHER THAN BP NOW)
    • NFP= negative (reabsorption)
  28. beginning of capillary (BP, OP, NPO)
    • BP= 15 (high
    • CoP=
  29. Net filtration pressure equation
    NFP= BP-CoP

    ex: BP-32 (-) CoP-22 (=) NFP-10
  30. NFP is 0 when...
    • midway through capillary where both are balance
    • -BP pushing out- 22mmHg
    • -CoP reabsorbing- 22mmHg
  31. NEGATIVE NFP at end of capillary bed means...
    did not reabsorb all fluid we filtered out earlier

    -filtered out 10 mmHg, only gained 70% back.... (bc NFP=-7)
  32. Lympatic system
    -excess fluid from capillary bed is absorbed by lympathic system

    • 1-way vessels drain into systemic venous circulation-thus regaining loss fluid and levels staying equal
    • (Lympatic veins-->lymphatic trunks-->lymphatic ducts-->subclavian veins to superior vena cava)
  33. lymph appearance
    • resembles plasma without the protein
    • looks more like interstitial fluid
  34. Venous system
    • always return blood to heart
    • systemic vein: leaves capillary bed with 15mmHg, pressure drops, but it must suffice to get blood ALL the way back to right heart
  35. veins structure
    • -large diameters
    • -small resistance to flow
    • -valves (prevent backflow) *esp important in lower limbs*
    • -large lumens
    • -high compliance can be DECREASED to stiffen wall
  36. Vericose veins
    • weak/loss elasticity in venous walls
    •    -veins widen and stretch
    •    -valves don't close (leading to back flow)
  37. function of veins
    • low pressure conduit back to heart
    • pressure reservoir (high compliance-easy to stretch walls)
  38. Vessels with high compliance can....
    elastic arteries/veins: tolerate large increase of volume with little increase of pressure
  39. AT REST 60% of blood volume is in...
  40. venous pressure determines...
    VENOUS RETURN (impacting stroke volume and CO)
  41. Factors increasing venous return:
    • -skeletal muscle pump
    • -respitory pump, 
    • -decrease compliance
    • -stiffening wall
    • -increase venous pressure
  42. skeletal muscle pump
    • -compression of veins by skeletal muscle contraction--raises venous pressure; valves prevent back flow
    • -blood forced towards heart
  43. respiratory pump

    --inhalation drops atmospheric pressure and explands lungs and cardiac channel (exercise effect)
  44. ONE input determining EDV
    venous return
  45. pulmonary circulation
    • low pressure system:
    • capillaries-->O2 blood venules-->4 pulmonary veins
  46. pulmonary-right heart PRESSURE
  47. pulmonary-artery PRESSURE
  48. pulmonary-MPAP PRESSURE
    diastolic 8 + 1/3 (17) = 14 mmHg
  49. Sources of resistance (opposition of flow): (pericarditis)
    • increased viscosity
    • blood vessel length
    • decrease radius
  50. compare r to R
    • r=radius
    • R=resistance

    VERY small changed in r --> BIG changes in R
  51. most important factor of resistance
  52. LaPlaces law:
    T (tension/force) ALPHA R (radius) * P (pressure in vessels)

    the tension/force stretching vessel is PROPORTIONAL to vessel diameter (or radius) * blood pressure


    • LESS tension on walls of SMALL vessels
    • more tension of walls of LARGE vessels (this is why aneurisms tend to occur in large vessels)
  53. compliance equation
    C= increase in V/increase in P
  54. relate compliance, volume and pressure
    HIGH compliance can accomodate LARGE increase increase in volume with SMALL increase in pressure

    (and vise versa) 

    low compliance (stiff vessels)-->small increase in volume--> large increase in pressure
  55. blood enters/leaves capillaries at what volume? what is the volume when blood enters veins
    • enter: appx 93 mmHg (MAP)
    • exit: appx 20 mmHg
    • enter veins: 10 mmHg
  56. Hormonal control in MAP regulation
    • EPI: vasoconstrictor, a1-adrenergic receptors
    •        vasodilator, vessels with B2-adrenergic        
    •        receptors
    • Angiotension II: strong vasoconstrictor, part of RAAS (renin-angitotensin-aldosterone system)
  57. arteriol pressure during DIASTOLE
  58. ventricular pressure during DIASTOLE
  59. Elastic arteries:
    • CONDUCTIVE ARTERY: get blood to tissue without losing too much energy.
    • 2.5-1.5 cm in diameter (aorta/pulm trunk)
    • high compliance, easy to stretch
  60. Muscular Arteries
    • 1cm-3mm in diameter
    • more smooth muscle 
    • dilate/constrict lumen
    • large lumem
  61. Lumen's role in muscular arteries
    small resistance to flow of blood. energy used for blood flow to small arteries
  62. laminar sound
    smooth flow (quiet)
  63. Turbulent flow
    blocking off, allows hearing
  64. failure of lympatic system leads to
    EDEMA: unable to p/u extra fluid 

    • failure due to:
    • Filariasis (tropical parasite)
    • chemotherapy
    • surgery
    • radiation
  65. Function of veins
    • low resistance flow back to RIGHT heart
    • blood reservoir (due to high compliance of venous walls, veins can accomodate large volumes of blood with relatively little increase in pressure)
    • venous pressure determines venous return
  66. blood reservoir
    high compliance of venous walls, veins can accomodate large volumes of blood with relatively little increase in pressure
  67. Major determinant in CO
    venous return
  68. determinants in venous return
    • total blood vol-->pressure-->VR
    • compliance-->(normally high) can be stiffened
    • sympathetic stim-->increase stiffness-->dec. compliance-->VP
    • valves
    • large lumen
    • skeletal muscle pumps
    • respiratory muscle pumps