Fill in the Blank QuestionFill in the blank question.A substance that is unlike other substances because it is both reabsorbed and secreted is .

The answer to the fill-in-the-blank question is "urea."

Urea is a waste product formed in the liver through the cycle of urea. It is unique among substances in that it is both reabsorbed and secreted by the kidneys during the process of urine formation. In the nephrons of the kidneys, urea can be reabsorbed back into the bloodstream after its initial filtration, depending on the body's needs and the hydration status of the individual. This reabsorption helps regulate the concentration of urea and, consequently, the solute concentration in the blood. Additionally, urea is secreted into the renal tubules to be excreted in urine, further demonstrating its dual role in kidney function. This capability of urea distinguishes it from many other substances that are either solely reabsorbed or solely secreted.