Glomerular capsule glucose and other organic solutes

Glomerular
capsule
Glucose
and other
organic
solutes
Osmotic
water
flow
Carrier protein
Countertransport pump Reabsorption
Secretion
Water reabsorption
Solute reabsorption
•
PCT is primary site of reabsorption:
•
> 99% organic materials (glucose,
amino acids, other nutrients)
• Ions, electrolytes (Na
+
, K
+
, HCO
3
-
,
Mg
2+
, phosphate, sulfate)
•
Water (~108 L/day)
•
As reabsorption occurs:
•
Solute concentration
decreases in tubular fluid
•
Water moves back into
peritubular capillary
(peritubular fluid)
• Mechanisms of reabsorption
•
Carrier proteins
•
Protein pumps
• Diffusion
•
Osmosis
Reabsorption
(24.10)
Figure 24.10
1

Urine storage
and elimination
Cells of
distal
convoluted
tubule
Peritubular
capillary
Peritubular
fluid
Tubular fluid
Toxins,
drugs
Toxins,
drugs
Distal
convoluted
tubule
Proximal
convoluted
tubule
Nephron loop
Collecting
duct
Glomerular
capsule
KEY
Diffusion
A
K
+
K
+ Na
+
K
+
Na
+
Na
+
H
+
Na
+
Na
+
Na
+
H
+
H
+
Glomerulus
Carrier protein
Countertransport
pump
Reabsorption
Secretion
•
Secretion occurs in DCT & PCT
•
Further modifies solute
composition of tubular fluid
•
In DCT, protein pumps allow
reabsorption & secretion to occur
in combination
•
Na
+
in exchange for K
+
•
Stimulated by
aldosterone
•
Na
+
in exchange for H
+
•
Carrier proteins secrete
toxins, drugs
•
Nitrogenous wastes,
ammonia
•
PCT secretes
•
Nitrogenous wastes, ammonia,
H+, some drugs
Secretion
(24.10)
Figure 24.10
2

The Nephron Loop Produces a Concentration Gradient
in the Medulla
(24.11)
•
Kidney’s ability to concentrate urine depends
on salt gradient in renal medulla
•
4x saltier in medulla than cortex
•
Nephron loop performs countercurrent
multiplication
• Countercurrent:
•
Fluid flows in opposite directions in adjacent
tubules of nephron loop
•
Multiplication:
•
Continuous flow of fluid causes ongoing
materials exchange with surrounding tissues
•
Continually & actively transports salt into renal
medulla
•
Ascending limb reabsorbs NaCl
• Salt accumulates in renal medulla
•
Causes higher salt concentration in medulla
than cortex
•
Sets up diffusion gradient for water
reabsorption
•
Descending limb reabsorbs water
600 600
900
900
900
1200
1200
100
Na
+
Cl
–
Na
+
Cl
–
Na
+
Cl
–
300
Na
+
Cl
–
H
2
O
H
2
O
H
2
O
300
300
Thin descending limb:
•
permeable to water
•
impermeable to solutes
•
solute concentration increases
Sodium and
chloride ions are
pumped out
Na
+
Cl
–
Na
+
Cl
–
Thick ascending limb:
• impermeable to water
•
selectively permeable to Na
+
and Cl
–
• solute concentration decreases
Renal medulla
Figure 24.11 3

•
Urea concentration increases in
tubular fluid as it moves through
nephron
•
Concentration of ions, toxins,
wastes, drugs also increases
•
Due to water reabsorption along
nephron & collecting system
•
Water reabsorption in DCT &
collecting duct variable
•
Urea concentration at papillary duct =
~450 mOsm/L
Urea Is Concentrated in Urine
(24.11)
KEY
KEY
Renal
cortex
Renal medulla
H
2
O
H
2
O
900
1200
1200
1200
100
300
300
300
300
1
2
3
H
2
O
H
2
O
= Impermeable to water = Impermeable to solutes
= Impermeable to urea;