Bioengineering 6000 CV Physiology
Kidney
Distal tubule
• Reabsorption:
– Na
+
, Cl
-
, HCO3
-
– Active transport of NaCl
– Water follows salts (permeability controlled
by ADH)
• Secretion:
– H
+
, NH
3
, K
+
– K
+
• Occurs when elevated in the body
• Na/K pumps into tubular cells, leaks
into tubule through channels
• Regulation/Feedback
– Distal tubule is close to glomerulus so
regulation based on osmolarity in tubule
– Concentrates urine
– Salt transport under endocrine control
‒ A
ldosterone: enhanced Na
+
reabsorption
and K
+
secretion
Adjustment of urine content
Bioengineering 6000 CV Physiology
Kidney
Collecting Duct
• Water permeable
– Permeability controlled by ADH through
cAMP signaling that increases aquaporin
formation
– Interstitial space is hypertonic (mostly from
NaCl and urea)
• Secretion of K
+
, H
+
, NH
3
• Reabsorption of Na
+
, Cl
-
, HCO
3
-
– Na
+
by active transport
– Regulated by aldosterone
– Determines water movement and urine
concentration
• Reabsorption of urea
– End of duct very permeable to urea
– Regulated by ADH by increase in urea
transporters
Final concentrating of urine
