PHGY 210 Lecture Notes - Lecture 45: Cotransporter, Sodium Chloride, Aorta

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21 Jul 2016
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the%machinery%is%the%sameN%mediated%by%tranceulllar%mediated%transport%and%diffusion.%The%most%
impt%substances%that%are%secreted%by%the%tubules%are%H%ions%and%K.%and%it%is%coupled%to%the%
reabsorption%of%na.%how%the%different%parts%of%the%tubule%divide%the%tasksN%since%the%body%is%making%a%
lot%of%waste%products,%the%gfr%is%large%and%so%many%ions%are%filtered.%So%a%lot%of%reabsorption%has%to%
happen.%The%PCT%reabsorbs%most%of%the%filtered%water%and%solutesN%it%is%the%most%quantitative.%It%is%a%
major%site%of%secretion%for%k.%by%the%time%the%fluid%reaches%the%DCT,%the%volume%of%water%and%solutes%
gets%small.%Fine%tuning%occurs%in%these%sections%and%homeostatic%controls%are%exerted%here.%%
!Concept%of%clearanceN%concept%that%is%not%usually%brought%up%in%other%organsN%the%volume%of%plasma%
from%which%the%substance%is%completely%removed%or%cleared%by%the%kidneys%per%unit%time.%the%
kindey%is%clearing%substances%from%the%plasma%into%the%urine,%and%this%is%the%amt%of%plasma%that%
completely%got%cleaned%out%for%that%particular%substance.%So%if%we%have%substance%s,%then%the%cs%is%
the%mass%of%s%excreted%per%unit%time%over%the%plasma%[]%and%this%is%gives%the%volume%that%got%cleared.%
So%you%need%to%know%the%amt%of%substance%s%(given%by%urine%[]%of%s)%and%multiplied%by%the%urine%
volume%to%get%total%[]%of%s,%divided%by%plasma%[].%This%is%impt%and%useful%to%estimate%the%GFR.%So%how%
do%we%do%this?%We%calculate%inulin%clearance—administer%iv’ly%and%is%frelly%filtered%in%the%
glomerulus,%and%its%not%reabsorbed%secreted%or%metabolized.%So%the%amt%of%inulin%that%gets%filtered%
will%appear%in%the%urine.%So%if%you%calcular%the%clearance%of%inulin,%this%is%the%same%as%the%gfr.%This%is%
why%the%concept%is%so%impt.%Inulin%clearance%is%still%the%most%accurate%way.%You%need%to%infuse%it%iv’ly%
and%maintain%a%steady%state%[]%4mg/ml.%when%filtered,%you%should%secrete%the%same%amt.%if%the%urine%
volume%is%2.4L/day,%and%the%inulin%[]%is%300mg/L%in%the%urine,%then%the%amt%of%inulin%is%2.4%x%300%and%
you%get%720%/%4=%180%L%day%as%the%GFR.%The%second%best%way%is%to%use%creatinine%clearance.%It%is%a%
waste%product%of%muscles,%and%the%only%difference%is%that%it%is%endogenous%and%you%don’t%need%to%
administer%it.%Its%not%as%perfect%as%inulin,%but%very%close.%You%need%urine%volume%and%[],%and%the%
plasma%[]%of%creatinine.%%
!ExampleN%patient%excreted%2L%per%day.%Take%small%amtN%creatinine%[]%was%9,6%mmol/L%and%the%
plasma%[]%was%.3%and%so%his%was%64L/day%(instead%of%180L).%he%needed%dialysis%and%then%got%a%kidney%
transplantation.%Usually%instead%of%mmol,%you%use%micromoles.%%
!GFR%is%specific%to%a%person,%but%clearance%is%specific%to%the%person%and%to%the%substance.%If%the%
clearance%is%>%GFRN%it%is%secreted%at%the%tubule.%If%<%gfr,%then%it%was%reabsorbed.%ParaNamino%
hippurateN%clearance%is%>%GFR%–%plasma%gets%cleared%of%the%substance%into%the%tubule%lumen%(so%net%
secretion).%So%the%clearance%will%be%equal%to%the%plasma%flow.%The%middle%and%end%column%has%net%
reabsorptionN%in%these%cases,%clearance%is%smaller%than%gfr.%%
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