Clinical Nutrition Exam 1 Practice

When the body is dehydrated, circulating volume drops and renal perfusion falls. The kidneys respond by conserving water and solutes, which concentrates the blood. Urea is reabsorbed more as flow through the tubules slows, so the BUN rises. At the same time, water loss is often greater than salt loss, especially with insensible losses or pure water deficits, so the serum sodium tends to increase. This combination—higher BUN from prerenal changes and higher sodium from proportional water loss—is the most typical lab pattern in dehydration. Hyponatremia or a low BUN would not fit the usual dehydration picture, while potassium changes are variable and not defining.