Re: [HAPS-L] Capillary Circulation

[Ken Saladin <ksaladin@xxxxxxxxxx>]

At 11:38 AM 7/14/2007, you wrote:
> I would like some help
> understanding this passage:
>  
> ?When
> the ambient temperature is cold... blood almost entirely bypasses the
> capillaries? Paradoxically, the skin may stay quite rosy because some
> blood gets ?trapped? in the superficial capillary loops as the shunts
> swing into operation; also, the chilled skin cells take up less O2.?
>  
> I don?t see a way for blood to become ?trapped? in capillaries since
> there is no ?post-capillary? sphincter.  I can see that the blood
> would not be forced out.  I assume that the reference to the low O2
> uptake is an explanation for why the blood stays
> red.


If the precapillary sphincters were strongly constricted, then there
would be little to no inflow into the distal capillary loops, and
therefore no pressure gradient to drive the blood out of those
capillaries -- just like water remaining in a garden hose after you turn
off the tap. You wouldn't need to close off the distal end of the garden
hose, or of a capillary, to retain fluid in it -- just stop applying
pressure to the proximal end.

Ken