Biomedical Core

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Biomedical Core
2013-03-13 00:51:24

Objective 22-26
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  1. Capillaries are specialized for exchange of
  2. Pressure-driven movement of fluid and solutes from blood capillaries into interstitial fluid is called
    filtration.  Oxygen, glucose, and other nutrients are delivered to the cells by filtration.
  3. Pressure-driven movement from interstitial fluid into blood capillaries is called
    reabsorption. Carbon dioxide, acid, urea, and other wastes are returned to the capillaries through reabsorption.
  4. The balance between hydrostatic pressure and interstitial fluid osmotic pressure forces is called the
    starling forces
  5. The equation which relates hydrostatic pressure and interstitial fluid osmotic pressure is called
    starling's law of the capillary
  6. Interstitial fluid osmotic pressure about the same throughout capillary, but hydrostatic pressure drops, this means the capillary delivers
    nutrients on the arteriole side, and picks up wastes on the venule side
  7. At the arterial end of the capillary, forces favor filtration:
    - Blood hydrostatic pressure (pushing), generated by the pumping action of the heart.

    Blood hydrostatic pressure decreases from 35 to 16 mmHg from the arterial to the venous end of the capillary.

    - Interstitial fluid osmotic pressure (pulling), which is constant at about 1 mmHg.
  8. At the venous end, forces favor reabsorption:
    - Blood colloid osmotic pressure (pulling), is due to the presence of plasma proteins too large to cross the capillary wall. Averages 36 mmHg

    - Interstitial fluid hydrostatic pressure, (pushing), which is normally close to zero mmHg, becomes a significant factor only in states of edema.
  9. Autoregulation in Capillaries:

    Precapillary sphincters are collars of
    smooth muscle.

    when relaxed, blood flows through capillary bed

    when contracted, blood bypasses capillary bed and takes thoroughfare channel
  10. The ability of capillaries to regulate blood flow is called
  11. Autoregulation is due to
    low oxygen in tissues
  12. Autoregulation increases the capillary blood flow
    - muscles undergoing metabolic demand

    - brain in areas of greater neural activity

    - skin autoregulates oxygen and nutrients; neural mechanisms control body temperature

    - lungs operate in an opposite

    • low O2 ------> vasoconstriction
    • high O-------> vasodilation
  13. These Vasoconstrictors raise blood pressure


    antidiuretic hormone (ADH)

    angiotensin II

    endothelium-derived factors (released in low blood flow)
  14. These Vasodilators lower blood pressure
    arterial natriuretic peptide

    nitric oxide

    • inflammatory mediators
    • histamine, prostacyclin, kinins
    • ethanol
    • inhibits ADH & vasomotor center
  15. Blood Flow:

                  PA - Pv
    flow =   ------------
    - R is resistance

    - V is the pressure difference between arteries and veins

    - Arterial pressure is PA

    - Venous pressure is Pv

    - Substitute these for V and we get I (flow)
  16. Blood Flow:

    R = nL/r4
    - n is blood viscosity

    - L is length of all blood vessels in the body

    - both of these don't change much

    • - we can and do change r (the radius of a vessel)
    • -r4 decreases resistance
    • -remember conductance = 1/R so conductance is related to the radius of the vessel to the fourth power: flow "a" r4
    • - the symbol "a" means - is proportional to-
    • - that is, flow = a constant times r4 
  17. Blood flow:

    flow "a" r4
    - when arteries lose their elasticity, patients lose the ability to regulate vessel diameter

    - Vessel diameter depends on the action of smooth muscle in arteries, arterioles and capillaries
  18. Decreased elasticity ------>
    hypertension (high blood pressure)
  19. Laminar flow describes the most efficient way
    liquids (such as blood) can flow
  20. Friction with walls of vessel ______ velocity at edges
  21. Flow rate is similar in concentric shells (laminae) so flow is called
  22. Turbulent flow occurs when
    laminar flow is disrupted

    Turbulent flow----> platelet shearing----> blood clotting
  23. Blood pressure (BP) is usually measured in the
    larger conducting arteries where the high and low pulsations of the heart can be detected.
  24. Systolic BP is the
    higher pressure measured during left ventricular systole, when the aortic valve is open
  25. Diastolic BP is the
    lower pressure measured during left ventricular diastole when the aortic valve is closed.
  26. A normal BP is less than ______ mmHg systolic and less than _____ mmHg diastolic. In young adult females, the pressures are often _____ mmHg less. People who are in good physical condition may have even ______ BPs.
    120; 80; 8-10; lower
  27. When blood pressure is measured, the blood pressure cuff, which is
    sphygmomanometer is inflated to a pressure greater than the systolic pressure of the blood. Blood flow is stopped and no sounds are heard.
  28. Slowly releasing air in the cuff, drops the pressure and blood begins to flow. The first sound heard is the .... Air continues to be released for the cuff. the ________ ______ is measured when no blood sounds are heard.
    systolic pressure; diastolic pressure
  29. Difference between systolic and diastolic pressure is greatest at
  30. As arteries decrease in caliber,
    pressure and pressure difference both drop

    By the time the blood reaches the venae cavae, pressure nearly zero.
  31. Muscles act as pumps to help
    venous blood return to heart