Practice Test 10

In a comparative physiology module, students examine why desert rodents can produce more concentrated urine than humans. Both species experience dehydration, but the rodents maintain plasma volume and osmolality more effectively. The instructor emphasizes that the difference is due to how renal structure supports endocrine control of water balance. Based on this scenario, which interaction is critical for maintaining homeostasis in the desert rodent?

A marathon runner collapses after finishing a race. She is confused, with nausea and headache. History reveals she consumed large volumes of plain water during the race. Labs show low plasma sodium and low plasma osmolality. The medical team suspects exercise-associated hyponatremia with impaired free-water excretion. Which change would most likely restore homeostasis in the described system?