about the clearance of PAH:
in a certain qn of kaplan(textbk) as the concentration of PAH in the blood rises, it's excretion increases. then shouldn't the clearance curve for PAH, with rising plasma levels, begin ascending? in the graph, the clearance curve descends, tending to approach the GFR.
IS THIS STATEMENT TRUE? "with rising plasma PAH levels, the venous levels of PAH begin to increase as the carriers for the secretion of PAH become saturated."
i just can't fix these facts together.
could the underlying answer be that a constant fraction of PAH is secreted...
in which case, the excretion of PAH increases with the increasing blood levels of PAH.
BUT THEN HOW DOES THE CLEARANCE CURVE DESCEND?
or does it descend because of greater number of carriers becoming saturated?
and have they forgotten to show that the curve begins ascending again?
as you can see, i've worked myself into a corner. please explain this. it's driving me up the kitchen wall...