renal physiology backgroundquine/biotopics07... · cocurrent and countercurrent mechanism what is...
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RENAL PHYSIOLOGY
Florida State UniversityAdvanced Topics in Biomedical Mathematics
MAP5932, Spring 2007 03/16/07
Brinda Pamulapati
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Goal
1 Background of the kidney2 Glomerulus3 Mathematical model of Glomerulus4 Co-current and counter- current mechanism5 Mathematical model of the co-current and
counter-current mechanism
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Kidney
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Kidney and Nephron picture
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Glomerulus and Bowman's Capsule
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Mathematical model of theglomerular filter
There are 3 pressures that effect the rate ofglomerular filtration:1 the pressure inside the glomerularcapillaries that promote filteration(p1)2 the pressure inside the Bowman's capsulethat opposes filtration(p2)3 the colloidal osmotic pressure of theplasma proteins inside the capillaries thatopposes filteration(pi)
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Schematic diagram of theglomerular filtration(one dimentional)
q1
q2
QiQe
x=0 x=L
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Mathematical model of theglomerular filter(cont.)
12 1( )f c
dqK P P
dx!= " +
cRTc! =
where osmotic pressure is
1 2
c
f
, hydrostatic pressure
osmotic pressure of the suspended protei ns and formed elements of the blood
K capillary filteration rate
P P
!
=
=
=
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Conservation Equation
( osmosis )cfrom RTc! =
1
1
1
i
1
/
(where )
i i
ci i
c i i
ic i i
c Q cq
c Q qRT
RTcQ q
QRTc
q
!
!
! ! !
=
=
=
= =
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Mathematical Model of theGlomerulus
12 1( )f c
dqK P P
dx!= " +
i
c i
i
Q
q! !=
................(20.1)
.......................................................(20.4)
ln 11
e
e i if
i i
Q
Q QK L
Q Q
!"
!! !
# $%& '
& '+ = %%& '
& '( )
..............(20.5)
i 1 2
=efflux through the efferent arterioles
L=length of the filter
= /( )
eQ
P P! " #
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Cocurrent and CountercurrentMechanism
What is Cocurrent and Countercurrent Mechanism
Why Study about it ?The human kidney use countercurrent exchange to remove waterfrom urine so the body can retain water that was used to move thenitrogenous waste products.
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Mathematical Model of theCocurrent and Countercurrent
Mechanism
1 11 2 1
2 22 1 2
( )
( )
C Cq d C C
t x
C Cq d C C
t x
! !+ = "
! !
! !+ = "
! !
.....................(20.15)
..................(20.16)
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Mathematical Problem
To Find: The outflow concentrationGiven : 1) The inflow concentration
2) The length of the exchangechamber
3) Flow velocities are known
Assume: Flows are in steady state The input concentrations are
0 0
1 2&C C
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( )
( ) ( )
( )
1
0
1
0
2 2
0
1 1 1
1
0
1
0
2 2 2
0 0
1 1 1 1
COCURRENT MECHANISM
1 1
1 1
1, , 1
COUNTERCURRENT MECHANISM
1
1, , 1
L
L
LC Le
C
C q d
C q q
C L e
C e
C L C q d
C C q q
!
!
!"# "#
# #
" # !#
"# # "#
#
" # !#
$
$
$
$
$
+ $= +
+ +
% &= = = +' (
) *
$ + $ +=
$
% &= = = $ = $' (
) *
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Conclusion
Total transfer of solute is always moreefficient with a countercurrent than with a
cocurrent.
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Sources
J.Keener, J.Sneyd, Mathematical Physiologyhttp://en.wikipedia.org/wiki/Image:Kidneys_from_behind.jp
ghttp://ocw.mit.edu/NR/rdonlyres/Health-Sciences-and Technology/HST-542JSpring-2004/BB83F266-3398-4154-A81D-
758E76A74EB5/0/renal_physiology.pdfhttp://coe.fgcu.edu/faculty/greenep/kidney/index.html
http://en.wikipedia.org/wiki/Countercurrent_exchange