Renal 7: Renal Mechanisms for Concentration/Dilution of Urine Flashcards
Where is the major site in which solute and water are separated?
Henle’s Loop
What value is the plasma osmolality held at?
300 mOsm/Kg H2O
What is antidiuresis?
state of dehydration that is typical for land dwellers.
What is the state of the following during antidiuresis? ADH water reabsorption urea reabsorption urine
Increased
Increased
Increased
Decreased (low volume high concentration urine)
What is diuresis
state of over-hydration. atypical and caused by administration of hypotonic solutions.
What is the state of the following during water diuresis? ADH water reabsorption urea reabsorption urine
Decreased
Decreased
Decreased
Increased (high volume, low concentration urine)
What is the osmolality of the following with respect to the plasma?
renal cortex
outer medulla
inner medulla
Renal Cortex: Isotonic
Outermedulla: mild hyperosmolality
Inner Medulla: strong hyperosmolality
What are the 3 major species and their % contribution to the gradient that contribute to the inner medullary hyperosmolality?
Na+(25%) Cl-(25%) urea (50%)
Rank the following from most to least hyperosmotic with respect to plasma:
outer medulla
inner medulla
renal cortex
inner medulla > outer medulla > cortex
What are the 3 mechanisms that generate and regulate medullary hyperosmolality?
Countercurrent Multiplier: generates initial osmotic gradient
Urea Cycle: Strengthens osmotic gradient
Countercurrent Exchanger: maintains osmotic gradient
What happens to the osmolality of the medullary interstitium during water diuresis?
reduced due to increased vasa recta blood flow and entry of some urea into collecting duct
No ADH so collecting duct is impermeable to water
What happens to the osmolality of the medullary interstitium during antidiuresis
Max ADH levels -> collecting duct highly permeable to water
Medullary interstitial gradient maxed
What is the countercurrent multiplier?
countercurrent flow in the 2 limbs of Henle’s loop that results in differential fluid and solute movements, generating vertical osmotic gradients
The thin descending loop of Henle has high/low water permeability, high/low salt permeability, and water/salt moves out of tubule.
high water permeability
low salt permeability
water moves out of tubule
The thin ascending loop of Henle has high/low water permeability, high/low salt permeability, and water/salt moves out of tubule
low water permeability
high salt permeability
salt moves out of tubule
What is the difference in salt movement between the thin and thick ascending limbs?
Thin: passive movement
Thick: active salt pumping
Where is the most active salt pumping site in the kidney?
Thick ascending loop of Henle
What part of the loop of Henle has high water perm. but low salt. perm.
Thin descending loop
What part of the loop of Henle has low water perm. but high salt. perm
Thin ascending loop
The thick ascending loop of Henle is diluting/concentrating segment. It becomes hyper/hypo-osmotic
Diluting segment
Hypoosmotic
Impermeable to water
What occurs in the distal tubule?
increased water permeabilty and salt transport -> reabsorption
What happens in the lower collecting duct but not the upper collecting duct?
Urea reabsorption
In the collecting duct, salt reabsorption is active/passive, and water reabsorption is active/passive.
active salt reabsorption
passive water reabsorption under ADH control
What occurs in the collecting duct?
active salt reabsorption and passive water reabsorption
What hormone regulates urea and water permeability in the lower collecting duct?
ADH
What is the path of urea from the upper collecting duct all the way around?
upper collecting duct (impermeable to urea) lower collecting duct (urea perm regulated by ADH inner medulla ascending vasa recta outer medulla descending thin loop of Henle tubular system (recycled through) lower collecting duct END OF 1 CYCLE
What are the 3 purposes of high medullary urea concentration?
- does not set up an osmotic gradient for the reabsorption of H2O
- protects vasa recta RBCs against crenation in a hyperosmotic environment
- sets up a gradient for urea to be excreted in low-volume urine
How does urea clearance vary with urinary flow rate?
directly, but passively and nonlinearly
More urea is lost to urine with increases in urinary flow rate
At what flow rate does urea clearance plateau? What does this mean for GFR?
flow rate greater than 10 mL/min. Then urea clearance estimates GFR
Describe the countercurrent exchanger
Water, salt, and urea move passively across vasa recta capillary walls in renal medulla.
What happens in the descending vasa recta
water moves out of capillary
salt and urea move into capillary
What happens in the ascending vasa recta
water moves into capillary
salt and urea move out of the capillary
At the end, the vasa recta exits the medulla with slightly more/less solutes than water.
slightly more solutes than water
What is water shunt with respect to countercurrent exchanger?
Excess water kept out of deep medulla
What is solute trapping with respect to countercurrent exchanger?
Excess solutes kept in lower medulla
What kinds of factors wash out the medullary gradient?
anything that increases the vasa recta blood flow -> washes out the medullary gradient and causes increased urine flow
^ vasa recta flow => v medullary osmolality ]> ^ urine flow (V)
How long does it take for the medullary osmotic gradient to be reestablished after it has been diluted?
few days (3 days)
What are the requirements for renal medullary hyperosmolarity?
long loops of henle
blood and urine flow
active salt pumping (TAL, DT, CD)
differential permeabilities of salt and water in thin ascending and descending loops
How do you calculate osmolar clearance?
C osm (ml/min) = Uosm * V/Posm = V* (Uosm/Posm)
What is the condition of urine when Uosm/Posm is more than 1?
concentrated urine -ADH antidiuresis
What is the condition of urine when Uosm/Posm is less than 1
dilute urine (water diuresis)
What is free water clearance (Ch2o)?
amount of pure water kidney adds to urine -> dilutes urine below osmolality of blood
(-) if kidney subtracts pure water from urine -> concentrate urine above blood osmolality
How do we calculate water clearance?
Ch2o = V-Cosm
What is negative free water clearance (-Ch2o)?
Uosm >Posm : dark amber urine
Water stolen from urine by kidney
What is positive free water clearance (Ch2o)
Uosm <Posm: pale dilute urine
Water is added to urine by kidney
What is tubular conservation of water?
TCh2o = -Ch2o
What is/are the endogenous factors controlling tubular water movement?
ADH
What are the exogenous factors that contribute to controlling tubular water movement?
Diuretics: furosemide (most potent, potassium wasting)
spironolactone: less potent, potassium sparing
