F u n c t i o n a l p r o c e s s e s in t h e n e p h r o n o f t h e k i d n e y • F i g u r e 1 5 . 4
Renal corpuscle
Renal tubule and collecting duct
Urine
(contains
excreted
substances)
Blood
(contains
reabsorbed
substances)
Substance
Filtered*
(enters glomerular
capsule per day)
Reabsorbed (returned to
blood per day)
Urine (excreted per day)
Water
180 liters
178-179 liters
1 - 2
liters
Proteins
2 . 0
g
1.9 g
0 . 1
g
Sodium ions
(Na+)
579 g
575 g
4 g
Chloride ions
(Cl-)
640 g
633.7 g
6.3 g
Bicarbonate
ions (HCO3-)
275 g
274.97 g
0.03 g
Glucose
162 g
162 g
0
g
Urea
54 g
24 g
30 gt
Potassium ions
(K+)
29.6 g
29.6 g
2 . 0
g*
Uric acid
8.5 g
7.7 g
0 . 8
g
Creatinine
1 . 6
g
0
g
1 . 6
g
*Assuming GFR is 180 liters per day.
♦ In addition to being filtered and reabsorbed, urea is secreted.
♦ After virtually all filtered K+ is reabsorbed in the convoluted tubules and nephron loop, a variable amount of K+ is secreted by principal cells in
the collecting duct.
The Urinary System Plays a Vital Role in Maintaining Homeostasis
445
I
Filtration:
In the
glomerulus, blood plasma
and dissolved substances
(smaller than most proteins)
get filtered into the
glomerular capsule.
I Reabsorption:
All along
the renal tubule and
collecting duct, water, ions,
and other substances get
reabsorbed from the renal
tubule lumen into the
peritubular capillaries and
ultimately into the blood.
(Secretion:
All along the renal
tubule and collecting duct,
substances such as wastes,
drugs, and excess ions get
secreted from the peritubular
capillaries into the renal tubule.
These substances ultimately
make their way into the urine.
p r o c e ss
diagram
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