Certain substances exit from the renal tubules to maintain the osmotic gradient in the medullary interstitium. What are they?

NaCl is actively transported from the ascending limb of the loop of Henle into the renal medulla, creating a high osmotic concentration in the medullary interstitium. Additionally, urea from the collecting duct also contributes to the hypertonicity of the medulla by diffusing into the interstitium. These processes are essential for the kidney's ability to concentrate urine and regulate water and solute balance in the body.