You are working in the free clinic when Father X comes in. You know him well; he is a type 2 diabetic who keeps his sugar under control with diet and exercise but is often in the clinic with homeless patients from the shelter he runs in the Episcopalian church down the block.
On this visit, Father X has brought in a thin man in his twenties named Joe. Joe appears confused and lethargic. He is breathing heavily and has a strong fruity odor. Father X tells you he is concerned about Joe because last night Joe was up every half-hour or so to use the bathroom and get water. Father X knows these are signs of diabetes, so he wants to get Joe checked out. He also tells you that Joe has not been drinking; they have a breathalyzer at the shelter, and Joe tested clean when he checked in the night before.
Joe's blood pressure is a little low at 95/60 mm Hg and his heart rate is a little high at 96 bpm. When you take his pulse, you notice that his skin is dry and "tents" up when pinched − a sign of dehydration. His respirations are more rapid than normal, 25 breaths/min, and heavy. His blood glucose is elevated at 320 mg/dL. His urine also contains glucose, and has a lower pH than normal. When you take his history he tells you that type 1 diabetes runs in his family.

Many of Joe's signs and symptoms can be related to the loss of glucose in his urine. Normally, urine does not contain glucose. When plasma glucose levels are elevated, however, some of the glucose from the plasma passes into the urine. Apply the principle of osmosis to explain why Joe was getting up all night to use the bathroom and why he has low blood pressure and signs of dehydration.

Choose the most accurate explanation for Joe's problem.

A. The frequent urination is happening because the urine contains a large volume of glucose. The loss of glucose from his plasma has decreased his blood volume.
B. The frequent urination is happening as part of a feedback loop to regulate his blood volume. It does not have anything to do with his plasma glucose.
C. The frequent urination is happening because his kidneys have stopped working. The kidney failure leads to low blood pressure.
D. The frequent urination is happening because when glucose moved into his urine, water also followed it. This removed water from his plasma, decreasing his blood volume and dehydrating him.