Which of the following substances has regulated reabsorption in the renal tubules?

• A. Creatinine
• B. Glucose
• C. Urea
• D. Sodium

Answer: (D)

Verified step by step guidance

1. Understand the concept of reabsorption in the renal tubules: Reabsorption is the process by which the kidneys recover water and solutes from the filtrate and return them to the blood. This process is crucial for maintaining homeostasis.
2. Identify substances that undergo regulated reabsorption: In the renal tubules, certain substances are reabsorbed in a regulated manner, meaning their reabsorption is controlled by various factors such as hormones and the body's needs.
3. Consider the role of sodium in the body: Sodium is a key electrolyte that helps regulate blood pressure, blood volume, and pH balance. Its reabsorption is tightly regulated by hormones like aldosterone.
4. Compare sodium with other substances listed: Creatinine is a waste product that is not reabsorbed; glucose is reabsorbed but not regulated in the same way as sodium; urea is partially reabsorbed but primarily excreted.
5. Conclude that sodium is the substance with regulated reabsorption: Due to its vital role in physiological processes, sodium's reabsorption is actively regulated in the renal tubules to maintain balance in the body.