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32 Cards in this Set

  • Front
  • Back
How is flow related to radius?
From Pouisielle's law, we saw that R=1/r^4. B/c Q=P/R, we can say that Q = r^4.
Thus, they are directly related.
At what range of pressure does autoregulation work?
Autoregulation if dependent on sympathetic innervation.
Autoregulation is an intrinsic property and independent of hormones and innervation.
What is the main goal of autoregulation?
To hold flow constant in the face of changing pressure.
How is myogenic tone induced?
Increased pressure causes increased activation of stretch receptors. This causes depolarization and thus contraction.
How does increasing myogenic tone affect flow?
Flow is reduced. Increased tone increases resistance.
Where does the myogenic tone mechanism take place?
In what kind of vessels?
Resistance vessels only - not in pulmonary or veinous circulation.
What two factors determine the concentration of breakdown products in interstitial fluid?
*metabolic rate of cells
*rate of "wash out"
Name three breakdown products that can act as vasodilators.
How can the metabolic mechanism compensate for an increase in MAP?
There will be increased washout of vasodilators, thus the vessels will constrict and increase resistance to keep flow down.
How could the metabolic mechanism compensate for reduced MAP?
There would be less flow, and thus less washout of vasodilators which would then accumulate and cause dilation. This reduces resistance and keeps flow from dropping.
How can an increase in metabolic rate result in an increase in O2 delivery?
What's another name for this?
There would be a higher concentration of vasodilating breakdown pdts and thus vasodilation. This would decrease resistance and increase flow and delivery of O2.
Exercise hyperemia.
What's the fundamental difference btwn autoregulation and metabolic regulation?
*autoreg seeks to maintain constant flow
*metabolic reg seeks to change flow to meet tissue demands
What are autocoids?
What are some examples?
Local tissue factors that are vasoactive. They are produced, act, and are degraded locally.
*NO, histamine
What is the action of NO?
How can it be reduced temporarily and permanently?
*increased fat intake temporarily reduces
*irreversibly falls with age
What is the action of angiotensin II and vasopressin on vessel tone? What are their effects on volume?
They both cause vasoconstriction in the resistance vessels. They stimulate retention in the kidney and thus increase volume.
Neural and hormonal mechanisms affect the venous and pulmonary circulation as well as arterial.
However, most intrinsic mechanisms affect only the arterial and arteriolar side.
What's the fundamental difference between the extrinsic and intrinsic mechanisms microcirculation control?
*extrinsic mechansims: seek to maintain constant MAP above all else
*intrinsic mechanisms: seek to maintain constant flow in tissue above all else
Which is stronger in skin circulation - intrinsic or extrinsic mechanisms?
Extrinsic - there is little metabolic activity here, thus little intrinsic control.
Which plays a bigger role in circulation to the cerebrum - intrinsic or extrinsic mechanisms?
Intrinsic: autocoid and metabolic vasodilation will quickly cancel any sympathetic constriction.
What is the simplified Starling equation?
CFR = Kf (Pc - COPp)
What does the constant Kf represent in the Starling equation?
*permeability of capillary wall to water
*the surface area over which filtration can occur
What does plasma hydrostatic pressure favor - filtration or absorption?
Filtration - movement out of the capillaries.
What does colloid osmotic pressure favor - filtration or resorption?
Resorption - the movement of fluid into the vasculature.
How might increased arteriolar resistance affect CFR? (There are 2 reasons)
This would reduce pressure in the capillary and thus reduce CFR.
Also fewer beds would be open and thus surface area for filtration (Kf) decreases.
How might decreased arteriolar constriction affect CFR? There are 2 reasons.
It would increase b/c more capillaries would open thus increasing the surface area available for filtration (Kf).
Also pressure in the capillaries (Pc) would increase.
How would increased CVP affect CFR?
Increased CVP would cause increased capillary pressure (Pc) and thus increased CFR.
There are two ways histamine contributes to edema - what are they?
*local vasodilator increases cap. P which increases CFR
*increases cap. permeability (Kf) which increases CFR
What is the major determinant of ultrafiltration?
Cap. hydrostatic pressure in more important than COPp or wall permeability.
Why is MAP less important than CVP in determining capillary hydrostatic pressure?
Myogenic autoregulation usually negates any changes in MAP.
How does dehydration affect CFR?
It raises the COPp, which decreases (Pc - COPp). This decreases CFR and resorption is favored.
How does hypoproteinemia affect CFR?
COPp decreases, so (Pc-COPp) is greater. CFR increases and filtration is favored.