Physio Question

[samtheman]

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Why does increase arteriolar vasoconstriction cause a decrease in Pc

 

[ACSurgeon]

Why does increase arteriolar vasoconstriction cause a decrease in Pc

b/a vasoconstriction upstream of the capillary bed results in less blood going to said capillary bed. Thus, less hydrostatic pressure.

I think a confusion physiologic concept is that vasoconstriction causes increased pressure in the body (global effect) due to increased resistance to blood flow but low blood flow locally.

Hope that helps.

 

[samtheman]

Which way is upstream and which way is downstream? Is it true that venoconstriction results in an increase in Pc?

b/a vasoconstriction upstream of the capillary bed results in less blood going to said capillary bed. Thus, less hydrostatic pressure.

I think a confusion physiologic concept is that vasoconstriction causes increased pressure in the body (global effect) due to increased resistance to blood flow but low blood flow locally.

Hope that helps.

 

[jsr52]

You can also visualize it this way. If you vasocontrict its like putting your thumb over a hose and the water comes out faster. So the flow of blood is increased and there is less time for blood to pool and go through capillary beds. Your sort of forcing blood to come to the venous side as fast as possible.

 

[ACSurgeon]

You can also visualize it this way. If you vasocontrict its like putting your thumb over a hose and the water comes out faster. So the flow of blood is increased and there is less time for blood to pool and go through capillary beds. Your sort of forcing blood to come to the venous side as fast as possible.

Actually, you're confusing flow and pressure. Vasoconstriction increased pressure but decreases local flow.

 

[ACSurgeon]

Which way is upstream and which way is downstream? Is it true that venoconstriction results in an increase in Pc?

Upstream is the arterial side before the capillary bed. Logically, venoconstriction should increase Pc, as the capillar blood is facing greater resistance to enter the venous circulation.

 

[ArcGurren]

Upstream is the arterial side before the capillary bed. Logically, venoconstriction should increase Pc, as the capillar blood is facing greater resistance to enter the venous circulation.

Yep, as such like the previous guy said, it's like putting a finger against a hose outlet and increasing the pressure inside the hose - whereas if you were to constrict the water before it really gets into the hose (i.e. arteriolar precapillary sphincters) then that's more like arteriolar vasoconstriction and less water is getting to it -> therefore decreased pressure on the capillaries -> decreased hydrostatic pressure.

 

[JRWhiter]

The more narrow a vessel, the greater the resistance. The greater the resistance, the lower the pressure. During arteriolar vasoconstriction, blood vessels become more narrow and thus blood flow is restricted. This causes less blood to flow into capillaries; thus, decreased caplillary pressure.

 

[samtheman]

b/a vasoconstriction upstream of the capillary bed results in less blood going to said capillary bed. Thus, less hydrostatic pressure.

I think a confusion physiologic concept is that vasoconstriction causes increased pressure in the body (global effect) due to increased resistance to blood flow but low blood flow locally.

Hope that helps.

TY👍