Urea - an ineffective osmole

Q: Urea is called an "ineffective osmole". What does it mean?


Answer: Urea equilibrates freely across the cell membranes, means when the plasma concentration of  urea changes, the intracellular concentration of the solute changes in parallel, and there is little or no water shift across the cells.

In contrast, glucose alters the balance and distribution of water across the cell membranes, and is called an "effective osmole".