How is urine flow rate quantified?
Urine flow rate UF
UF = Urine volume / Collection interval
How is renal clearance of a solute calculated?
How about renal excretion?
Cx = (Ux/Px)*UF
Ex = (Ux)*UF
This is intuitive; the urinary concentration or ratio of urinary to plasma concentrations, times the flow rate.
How is osmolar clearance calculated?
How is renal free water clearance? What is the significance of this?
Cosm = (Uosm/Posm)*UF (this is renal clearance for all solutes)
CH2O = UF - Cosm (This reveals the relative tonicity of urine. If hypertonic, this is negative; if isotonic, it is zero; and if hypotonic, it is positive.
Calculate the urine flow rate, osmolar and free water clearance, and sodium excretion in this patient. Try to not use a calculator!
Volume collected: 150mL
Vosm: 900mOsm, Posm: 300mOsm
UF: 0.5 mL/min
Cosm: 1.5 mL/min
CH2O: -1.0 mL/min
What are some fairly typical ranges for urine flow, osmolar and free water clearances in a hydrated, but not volume-loaded person at rest?
Urine flow: ~0.5 - 1mL/min (recall: 125mL filtered, 124mL reabsorbed)
Cosm: ~1.5 - 2.0 mL/min
CH2O: ~-0.5 - -1.5 mL/min (urine is "typically" hypertonic)
What are the effects of water consumption on renal parameters?
Increased urinary flow rate, of which osmolarity is low. Time-normalized electrolyte excretion is normal.
What are the effects of beer consumption on renal parameters?
Incrase in urinary flow rate, moreso than with water because of alcohol's anti-ADH effect. Maybe some increased electrolyte excretion, depends on the composition of beer.
If urinary osmolarity is less than plasma osmolarity, what can be said of the free water clearance?
It must be positive.
CH2O = UF * (Uosm/Posm)*UF
CH2O = UF * (1 - Uosm/Posm)
Compare the relative efficacies of acetazolamide and furosemide as diuretics.
Furosemide is massively more powerful as a diuretic than acetazolamide, and also causes more electrolyte wasting.
What is the main source of feedback for kidney control & regulation?
The juxtaglomerular apparatus.
How will the body fluid compartments change in composition with administration of a hypertonic solution?
ICF loses volume due to flux of water to the ECF. Both compartments increase osmolarity.
What is the effect of renal sympathetic nerve stimulation?
Increase of both renin and sodium reabsorption.
These effects are both pro-retention; think of these processes as countering loss of volume due to injury/exsanguination.
What is the effect on the urine of bicarbonate consumption?
Why does potassium excretion increase?
Urine becomes alkalotic.
Intercalated cells secrete potassium in order to retain hydrogen ion, to counter plasma alkalosis.
Compare and contrast the effects of bicarbonate and acetazolamide treatment.
Both increase sodium and potassium excretion. The bicarbonate solution may have higher free water clearance, as acetazolamide's osmolar clearance seems higher (depends on solution concentration).