Question

1. In your own words, explain why an animal with excessively high blood osmotic pressure must be able to produce urine hyperosmotic to its blood plasma if its kidneys are to help correct the problem. In your answer, explain why neither urine that is isosmotic to the blood plasma nor urine that is hyposmotic to the plasma would help.

Answer 1

Ans: If the blood osmotic pressure is too high, the animal must excrete concentrated urine containing more solute than water. This will decrease solute concentration in blood and bring down osmotic pressure to normal. Hyperosmotic urine means secretion of urine that has a higher solute to the H₂O ratio than blood.

• If isosmotic urine was removed, then it would have filtered the blood as it is which means the volume of unfiltered blood would have been reduced but solute to H₂O content would be unaltered.
• If hyposmotic urine was removed, blood would have become more concentrated than the current state.