Osmoregulation Problem Set

Osmoregulation Problem Set 1. What would be the osmotic pressure (in Osmoles) of a 0.2 M CaCl2 solution ? If a 1 Osm solution freezes at -1.86 C, what would be the freezing point of this solution? (assume full dissociation, ie. activity coefficient of 1.0).

2. If urine concentration (U) of a solute that is neither secreted nor reabsorbed by the kidney tubules is 30 mg/ml and the urine flow rate (V) is 1 ml/min, and if the plasma concentration of the solute (P) is equilibrated at 5 mg/ml, what is the glomerular filtration rate (GFR) ? What % of filtrate is being reabsorbed by the kidney ?

3. A particular substance (Z) is present at concentrations of 1 mg/ml in the plasma and 10 mg/ml in the urine. The urine flow rate is 10 ml/min. What is the clearance of the substance ? Compare this with the GFR obtained in Question 2, and determine whether Z is secreted or reabsorbed.

4. What happens when the Tm (transport maximum) of reabsorption is exceeded for a solute ?

5. Why is there a trend toward longer Loop of Henle in xeric (desert) mammals ?

6. You collect the following data: plasma Na = 144 mM, urine Na = 200 m M, urine volume = 36 ml in 30 min. and inulin clearance = 120 ml/min. What percentage of filtered Na is excreted ?