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
What osmolarity is the max our kidneys can produce?
1200-1400 mOsm/L
Antidiuresis requires what 2 things?
High ADH
High osmolality of renal medullary interstitial fluid
Which has a higher concentration of urea, the CCD or the DT?
CCD, the DT is impermeable to urea
Describe the water permeability of the collecting ducts when ADH levels are high
High ADH increaes the water permeability of the collecting ducts to very high levels
[High ADH also increases the permeability of the apical membrane of the thick ascending limb to NaCl, leading to an increase in the osmolality of the peritubular interstitium (d/t countercurrent multiplication). These effects combined result in water being rapidly reabsorbed from the cortical and outer medullary portions of the collecting duct system via aquaporin water channels, resulting in the production of a small volume of hypertonic urine, with osmolality approaching that of the inner medullary interstitium]
During antidiuresis:
______ in ADH
_____ in urea concentration in CD
Increase
Increase
[urea will passively diffuse out of the tubule]
What role does the vasa recta play in the hyperosmolarity of the medulla?
VR minimizes solute washout from the interstitium - thus it does not create the hyperosmolarity but plays a role in preventing it from being dissipated
The total clearance of solutes from the blood can be expressed as ______ ________; this is the volume of plasma cleared of solutes each minute in the same way that clearance of a single substance is calculated
Osmolar clearance
Osmolar clearance equation
Cosm = (Uosm x V)/Posm
_______ ______ ______ = rate at which the body excretes solute-free water
Free water clearance
Equation for free water clearance
C(H2O) = V - C(osm)
What does it mean when C(H2O) is negative?
Excess solutes are removed; water is being conserved
What does it mean when C(H2O) is positive?
Water is being excreted, forming dilute urine, water is in excess
_______ _______ = Percentage of filtered substance that actually gets excreted
Fractional excretion
Equation for fractional excretion
(Ux)(PCr)/(Px)(UCr)
Interpret a fractional excretion of 1.0
100% of what gets filtered is excreted
Interpret a fractional excretion of 0.9
90% of what is filtered gets excreted (reabsorption has occurred!)
Interpret a fractional excretion of 1.1
110% of what gets filtered gets excreted (secretion occurred!)
A FeNa of below 1% would indicate what type of AKI?
Pre-renal
The physiologic response to a decrease in renal perfusion is an increase in sodium reabsorption to control hyponatremia, often caused by volume depletion or decrease in ECV (e.g., low output heart failure)
A FeNa of above 2% would indicate what type of AKI?
Intra-renal or post-renal
Either excess sodium is lost d/t tubular damage, or the damaged glomeruli result in hypovolemia resulting in the normal response of sodium wasting
What 2 conditions relating to sodium and water balance does chronic SIADH lead to?
Hyponatremia
Euvolemia (TBW slightly increased)
Possible underlying causes of euvolemic hyponatremia
SIADH
COPD
Malignancy
Possible causes of hypervolemic hyponatremia
CHF
Renal impairment
Cirrhosis
3 P’s of diabetes insipidus
Polyuria
Polydipsia
Polyphagia
Central diabetes insipidus
Deficient secretion of ADH from hypothalamus or pituitary
Nephrogenic diabetes insipidus
Renal insensitivity to ADH
SIADH effect on:
Urinary output ADH levels Plasma sodium Hydration status Thirst Body water content
Urinary output decrease
ADH level increase
Plasma sodium decrease
Hydration status increase
Thirst increase
Body water content normal or slightly increased
Diabetes insipidus effect on:
Urinary output ADH levels Plasma sodium Hydration status Thirst Body water content
Urinary output increase
ADH decrease (central) or same (nephrogenic)
Plasma sodium increase
Hydration status decrease
Thirst increase
Body water content decrease
