Test 2: Wk6: 1 Renal transport mechanisms and clearance - Mangiarua Flashcards
3 basic renal processes
1 glomerular filtration
2 tubular secretion
3 tubular reabsorbtion
Glomerular filtration
bulk-flow of essentially protein-free plasma from the
glomerular capillaries into Bowman’s capsule.
Glomerular filtration is what type of transport
passive; no active
Tubular secretion
transfer of materials from the peritubular-capillary plasma to the
tubular lumen
Tubular secretion transport
Both active and passive transport
Tubular secretion selectivity
high
tubular secretion occurs where
throughout the length of the nephron
Tubular reabsorption
transfer of materials from the lumen of the tubule to the
peritubular-capillary plasma.
Tubular reabsorption selectivity
high
Tubular reabsorption transport
Both active and passive transport
tubular reabsorption occurs where
throughout the length of the nephron
— charged macromolecules are
restricted far more than —molecules, while — charged molecules
are restricted less.
negative, neutral, positive
As molecular weight (and therefore size) —, filterability —, so
that proteins with a molecular weight above — d are hardly filtered at all.
increase, declines, 70,000
best index of kidney function
GFR
GFR 60-89
mild kidney dz
GFR 30-59
Moderate chronic renal insufficiency
GFR 15-29
Severe chronic renal insufficiency
GFR <15
End Stage Renal Failure
Renal Clearance
volume of plasma from which all of a substance has been removed and excreted into urine per unit time
What is used for Measurement of GFR
inulin
— is freely filtered at the glomerulus and not reabsorbed or secreted into tubule
inulin
GFR =
urine flow x inulin conc. urine / inulin conc. plasma
GFR = V x Uin / Pin
In order to determine the rate at which plasma is filtered into Bowman’s space, a chemical which meets the following criteria is used (6)
1) Not bound to plasma proteins.
2) Not electrically charged.
3) Freely filtered.
4) Not lost by reabsorption from tubular fluid to peritubular fluid.
5) Not gained by secretion from peritubular fluid into tubular fluid.
6) All that is filtered is excreted.
Clearance of Inulin
GFR = Uin x V / Pin = Cin
Inulin clearance refers to the
Inulin clearance refers to the milliliters of plasma from which all inulin has been removed by the kidney each minute
Inulin clearance is independent of
plasma inulin conc. and urine flow
Creatinine
endogenous substance that estimates GFR
Clearance of Creatinine
GFR = Ccr = Ucr x V / Pcr
Creatinine — GFR
slightly overestimates
— concentration is used to follow pts over long period of chronic renal dz
Creatinine
Renal Clearance Ca =
Ca = Va x V / Pa
Ca > Cin
cleared by filtration and secretion
Cb < Cin
some of b is reabsorbed
Diffusion:
- requires an electrochemical gradient,
* “downhill” transport
Facilitated diffusion:
requires an electrochemical gradient + carriers; exhibits
specificity, saturability, and competition,
• “downhill” transport.
Primary active transport
requires carriers; exhibits specificity, saturability, and
competition,
• “uphill” transport. Requires energy; splitting of ATP.
Secondary active transport
• requires carriers; exhibits specificity, saturability, and
competition,
• one substance “downhill” transport, the other “uphill”
transport,
• cotransport (or symport),
• countertransport (or antiport).
diffusion between cells
paracellular
“across” the cell
transcellular
— used for measurement of effective renal plasma flow
PAH
PAH is filtered —
at glomerulus
PAH undergoes no significant
tubular reabsorbtion
— can be used to estimate RPF (Renal Plasma Flow)
Clearance of PAH
PAH is a foreign compound so it needs to be
infused
ERPF
Effective Renal Plasma Flow
ERPF =
ERPF = CPAH = V x UPAH / PPAH
the effective renal plasma flow Underestimates true RPF by —%
10%
The actual renal plasma flow can be obtained by dividing the — by —
ERPF by excretion ratio of PAH
equation for calculation RPF
E = A - V / A
A conc. in renal arterial plasma
V conc. in renal venous plasma
Urate filterability
free
more than 90% if filtered urate is reabsorbed where
early in prox tubule
urate secretion
active tubular secretion in late prox tubule
urate is — regulated
homeostatically
urate undergoes both — and —
active reabsorption and active secretion
K filterability
free
67% of K reabsorbed in
prox tubule
20% of K is reabsorbed in
TAL of LOH
— is reabsorbed or secreted in the late nephron depending on diet
K
K is — regulated
homeostatically
Reabsorption rate =
Filtered load – Excretion rate
Secretion rate =
Excretion rate – Filtered load
Filtered load =
GFR x [plasma]
Excretion rate =
V x [urine]
