Kidney Function 2 Flashcards
ADH/vasopressin
- increases water reabsorption in the collecting duct
- increases permeability of CD and DCT by inducing aquaporin channels into the plasma membrane
- increases peripheral vascular resistance which increases arterial BP
Aldosterone
- acts on DT and CD
- increases reabsorption of ions and water
- conservation of Na
- secretion of K
- water retention
- increased BP
What hormones control Na and water reabsorption?
- ADH/vasopressin (water)
- aldosterone (Na)
What hormones control Ca2+ reabsorption?
- parathyroid hormone (PT)
- vitamin D3 (DT)
- both favour retention
What percent of water is excreted?
1%
What percent of Na is excreted?
0.5%
What percent of K is excreted?
10%
What percent of Ca2+ is excreted?
2%
What percent of phosphate is excreted?
20%
What percent of glucose is excreted?
0% (if plasma concentration is <15mmol)
What percent of creatinine is excreted?
100%
(filtered, not reabsorbed, secreted to a small extent)
What percent of urea is excreted?
50%
Na is reabsorbed
actively, through the cell into ECF via Na/K-ATPase on basolateral (ECF) side
reabsorption on the apical membrane varies with region of nephron
In the proximal tubule, Na is reabsorbed on the apical membrane via
- Na/glucose cotransporter
- Na/AA cotransporter
- Na/PO4 cotransporter
- etc.
Reabsorption of Cl and HCO3 is driven by
- Na reabsorption leaving a -ve charge in the lumen, forming an electrochemical gradient (~3mV)
- negatively charged ions Cl and HCO3 tf drawn across membrane:
- HCO3 transcellularly
- Cl via paracellular space
- water follows both transcellularly and paracellularly via osmotic gradient created by Cl movement
What is solvent drag?
- applies only at PT
- as water is reabsorbed, solutes are concentrated in the lumen
- movement of H2O via paracellular pathway carrying solutes dissolved in it:
- K, Ca, urea
How are Cl and HCO3 reabsorbed in the proximal tubule?
early PT:
- HCO3 transcellularly via electrochemical gradient
- tf increased [Cl] in early PT
- increased -ve charge of lumen draws Na+ back via paracellular spaces
late PT:
- increased [Cl] from HCO3 reabsorption establishes a concentration gradient for Cl
- Cl moves out of the lumen, reabsorbed via paracellular spaces
- occurs faster than Na+ leaves; est +3mV in lumen
- Na+ moves transcellularly and paracellularly w/Cl,
How does Na reabsorption occur in the tALH?
- passively via paracellular spaces due to concentration gradient:
- Na is high in lumen (1200mOs predominantly NaCl)
- Na is relatively low in ECF (1200mOs 2/3 NaCl, 1/3 urea)
- tf Na moves passively from lumen to ECF
How is Na reabsorbed in the TALH?
- actively, driven by Na/K ATP-ase on basolateral (ECF) side
- Na enters apical membrane via Na/K/Cl co-transporter (target for frusemide)
- uses gradient generated by Na/K ATP-ase
- some Na flows through paracellular pathway but junctions are much tighter in TALH to prevent water movement
How is Na reabsorbed in the DT?
- enters apical membrane and proceeds transcellularly via Na/Cl transporter (target of thiazide diuretics)
- actively reabsorbed on basolateral membrane via Na/K-ATPase
How is Na reabsorbed in the CD?
- passively on apical membrane via ENaC (epithelial Na channeL0
- actively on basolateral surface via Na/K-ATPase
- K+ is passively secreted into lumen
How is urine concentrated in the LOH?
- active transport of Na, Cl, K into the medullary interstitium increases osmolarity
- water is drawn out of the descending LOH across osmotic gradient to equilibriate with interstitium
- more fluid enters loop and the cycle repeats
- concentration of urine increases down descending LOH
- concentration of urine decreases up ascending LOH
