Download Renal lecture problems

Answers to renal physiology
problems worked in class
Robert G. Carroll, Ph.D.
Brody School of Medicine
East Carolina University
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notes at beginning slide of each
problem
Renal Processes Problem
Assume RPF = 625 ml/min, GFR = 125 ml/min
[plasma]
Renal
Delivery
Tubular
Load
Urinary
Excretion
1
7 mg/dl
43.75
mg/min
0 mg/min
0 mg/min
2
100 mg/dl 625
mg/min
125
mg/min
0 mg/min
3
140 mEq/l 87.5
mEq/min
17.5
mEq/min
0.18
mEq/min
4
1 mg/dl
6.25
mg/min
1.25
mg/min
1.25
mg/min
5
10
units/ml
6250
units/min
1250
units/min
3000
units/min
Renal Processes Problem
Assume RPF = 625 ml/min, GFR = 125 ml/min
1
Not filtered, protein
[plasma]
Renal
Delivery
Tubular
Load
Urinary
Excretion
7 mg/dl
43.75
mg/min
0 mg/min
0 mg/min
2
Filt, reabs glucose
100 mg/dl 625
mg/min
125
mg/min
0 mg/min
3
Filt, reabs Na
140 mEq/l 87.5
mEq/min
17.5
mEq/min
0.18
mEq/min
1 mg/dl
6.25
mg/min
1.25
mg/min
1.25
mg/min
10
units/ml
6250
units/min
1250
units/min
3000
units/min
4
Filtered creatinine
5
Filt, secr Penicillin
Problem - GFR
What is the consequence of
• Afferent arteriole constriction
• Afferent arteriole dilation
• Efferent arteriole constriction
• Efferent arteriole dilation, on
Renal blood flow?
Glomerular filtration?
Peritubular capillary reabsorption?
Renal blood flow and GFR
•
Aff. Constr
Eff. Constr
Aff. Dilate
Eff. Dilate
RBF
GFR
Peri Reabs
Reasoning behind problem
Aff. Arteriole
Eff. Arteriole
Glom cap
Bowman’s
Capsule
Peritub
cap
Aff or Eff contraction decreases peritubular
capillary hydrostatic pressure, and increase
peritubular capillary reabsorption
Aff. Arteriole
Eff. Arteriole
Glom cap
Bowman’s
Capsule
Peritub
cap
Aff contraction decreases glom cap hydrostatic
pressure, and GFR. Eff contraction increases glom
cap hydrostatic pressure and increases GFR
Aff. Arteriole
Eff. Arteriole
Glom cap
Bowman’s
Capsule
Peritub
cap
Renal blood flow and GFR
•
Aff. Constr
Eff. Constr
Aff. Dilate
Eff. Dilate
RBF
GFR
Peri Reabs
Proximal Tubule Problem
Carbonic anhydrase can be inhibited
by acetazolamide.
Will this alter the tubular reabsorption
of:
Na
Water
Cl
Glucose
K
Proximal Tubule Problem Solution
Na absorption is reduced.
Na absorption depends on 1) proton
secretion across the apical surface,
and 2) a counter ion being absorbed
with the Na. Intracellular carbonic
anhydrase helps generate the proton,
and luminal carbonic anhydrase
generates the HCO3. Blockade of
carbonic anhydrase diminishes both
steps.
Proximal Tubule Problem Answer
Water absorption reduced.
Water movement is passive,
dependent on an osmotic gradient. If
Na and HCO3 are not absorbed,
filtrate remains isotonic with plasma,
and no osmotic gradient exists
Proximal Tubule Problem Answer
Cl absorption is decreased.
Cl absorption in the proximal tubule
is dependent on a Cl concentration
gradient. If water is not absorbed
from the filtrate, filtrate Cl
concentration is identical to plasma
Proximal Tubule Problem Answer
Glucose reabsorption is normal. As
long as there is Na available to drive
the secondary active transport,
proximal tubule glucose reabsorption
will proceed normally
Proximal Tubule Problem Answer
K reabsorption is decreased.
K reabsorption in the proximal tubule
is dependent on a K concentration
gradient. If water is not reabsorbed
from the filtrate, filtrate K
concentration is identical to plasma.
Proximal Tubule Problem Answer
Carbonic anhydrase can be inhibited by
acetazolamide.
Will this alter the proximal tubular reabsorption
of:
Na YES
Water YES
Cl YES
Glucose NO
K YES
Problem
• Amiloride blocks Na entry through the
apical channel
• What happens to luminal Na+
• What happens to luminal K+
Amiloride problem answer
• What happens to luminal Na+?
• Na+ entry across the apical surface
of the principal cell occurs through
the Na channel. If the Na channel is
blocked, then Na remains in the
lumen, so luminal Na content is
increased (compared to normal).
Amiloride Problem Answer
• What happens to luminal K+?
• Identical K channels exist on the apical
and basolateral surfaces of the principal
cells. K secretion into the lumen requires
the development of a negative
transepithelial potential. If Na does not
enter the cell on the apical surface, then
the transepithelial potential does not
develop, and K does not cross the apical
surface into the lumen.
Amiloride Problem Answer
• Potassium wasting diuretics.
• If distal tubule Na delivery is increased, then
Na entry on the principal cell apical surface is
increased. This results in enhanced K
secretion into the lumen, and enhanced K loss
from the body. Any diuretic that impairs Na
absorption before the distal tubule is classified
as K wasting.
Amiloride Problem Answer
• Aldosterone and Potassium wasting
• Aldosterone is required for diuretics to
“waste” potassium. Aldosterone
stimulates the basolateral Na/K ATPase
to assist the transepithelial reabsorption
of Na.
• A high salt diet also increases distal
tubule Na delivery, but because
aldosterone is low, potassium wasting
does NOT occur
Amiloride Problem Answer
• Potassium sparing diuretics
• Only those diuretics that act on the
principal cells are considered K sparing.
This is because if the apical entry of Na
is blocked, then the transepithelial
potential does not develop, and K
secretion (loss) does not occur.
Potassium sparing diuretics
Distal Tubule and
Cortical Collecting Duct
Lumen
amiloride
Capillary
Na+
-70 mV
K
+
K
+
+
Na
K
K
Transepithelial potential -5 to -70 mV
+
+