Mechanisms To Adjust Urine Concentration Flashcards
Describe water and sodium permeability in the thin descending segment of the LOH
Water permeable
NaCl remains in the tubule and concentrates during the descent
Describe water and sodium permeability in the thin and thick ascending LOH
Water impermeable
NaCl is reabsorbed in the tubule - dilutes during ascent
In the thick ascending LOH, Na/K ATPase maintains ____ intracellular Na and favors movement of Na from lumen into cell via _______ co-transporter and _____ countertransporter
Luminal electrochemical gradient favors movement of other positively charged ions out of the tubule
There is passive leakage of ____ and _____
Low; Na-K-2Cl; Na-H
K+ and Cl-
T/F: Loop diuretics will reduce magnitude of lumen-positive charge
True
Early DT reabsorbs what ions? Is it water permeable or impermeable?
reabsorbs Na, Cl, Ca
Water impermeable
Late DT cell types and their permeability/functions
Principal cells: Na+ reabsorption, K+ secretion, water reabsorption
Intercalated cells: acid-base balance
Do thiazide drugs act on early or late segment of DT?
Early, at the NCC channel
What diuretcs act at late DT?
K-sparing diuretics act on principal cells
Na channel blockers (amiloride, triamterene)
Which region/cells of the nephron respond in conditions of acidosis and what is the mechanism?
Late segment DT: alpha-intercalated cells
Convert carbonic acid to bicarb and H+
H+ ATPase and H/K ATPase transporters move H+ out of the cell into tubular lumen
H+ is excreted and HCO3 is reabsorbed
Which region/cells of the nephron respond in conditions of alkalosis and what is the mechanism?
Late segment DT: beta intercalated cells
Carbonic acid is converted to bicarb and H+
H+ ATPase and H/K ATPase transporters move H+ out of the cell into renal interstitium
H+ is reabsorbed and bicarb is secreted
What hormones regulate water permeability at the leate DT and CCD and what are their actions?
ADH -> upregulates aquaporin 2 in apical membrane
ANP and BNP inhibit ADH
T/F: Water transport along the nephron is active
False; passive!
Describe passive reabsorption of Cl
Chloride follows sodium
- Transport of Na+ leaves a negative charge behind that pushes Cl- from the area
- When water is reabsorbed, solutes are concentrated behind it, Cl- can build up. Cl- will passively diffuse away as a result
Describe active reabsorption of Cl-
Na-Cl co-transporter (distal tubule)
Na-K-2Cl co-transporter (TAL)
2 components of countercurrent multiplier mechanism
- The single effect
2. Fluid flow
What determines the size of the gradient generated by CC multiplier mechanism?
The length of the LOH
CC multiplier mechanism consists of single effect and fluid flow. Describe the single effect
NaCl leaves the ascending limb, interstitium becomes hyperosmotic
Water leaves descending limb in attempt to equalize the interstitium osmolality
CC multiplier mechanism consists of single effect and fluid flow. The single effect is when NaCl leaves the ascending limb, interstitium becomes hyperosmotic. Water then leaves descending limb in attempt to equalize the interstitium osmolality.
Describe the fluid flow aspect of CC multiplication
Fluid is always flowing through the tubule; new fluid enters descending limb from above, pushing tubular fluid downward and developing a gradient –> multiplies the effect of the single effect
During CC exchange: reabsorbed water is returned to the circulatory system via the _____ _____. Because the blood flow through these capillaries is very ______, any solutes that are reabsorbed into the bloodstream diffuse back into the interstitial fluid, which maintains the solute gradient in the medulla.
Vasa recta
Slow
Describe urea recycling
Urea in the interstitium drives up osmolality, which further enhances passive water reabsorption in the LOH. The recirculation of urea helps trap urea in renal medulla and contributes to hyperosmolarity of the renal medulla.
Renal transporters:
UT-AI and UT-A3 (medullary CD)
UT-A2 (thin limb)
Activated by ADH
What happens to urea cycling if you eat a high protein diet?
More urea in the body helping to concentrate medullary interstitium - so you will generate more concentrated urine
Medullary osmolallity is due to the presence of what 2 compounds?
NaCl and urea
________ = continuous reabsorption of solutes and failure to reabsorb water leading to high urine volume and low medullary solute concentrations
Diuresis
______ ______ ______ is calculated based on the idea that the maximal concentrating ability of the kidney dictates how much urine volume must be excreted each day to rid the body of metabolic waste products and ions that are ingested
Obligatory urine volum
