Which of the following substances is NOT selectively reabsorbed as the urine flows along the tubules?

Correct option is C

​The correct answer is (c) Urea.

Explanation:

Urea is a waste product formed in the liver through protein metabolism and is not selectively reabsorbed in the kidneys. Instead, it is filtered into the urine by the glomerulus and passes through the renal tubules, where most of it remains in the urine for excretion.

In contrast, glucose, amino acids, and salts are essential substances that the body needs to retain. These are selectively reabsorbed back into the bloodstream as the urine flows through the renal tubules to maintain proper body function and homeostasis.

• Glucose and Amino Acids are almost completely reabsorbed from the proximal convoluted tubule into the blood under normal conditions.
• Salts (like sodium) are reabsorbed at different segments of the renal tubule depending on the body's needs.

Information Booster:

• Selective Reabsorption:
  The process by which the kidneys selectively reabsorb useful substances (like glucose, amino acids, and salts) from the filtrate back into the blood is vital for maintaining body fluid balance, electrolyte balance, and preventing the loss of essential nutrients.
• Role of Urea:
  Urea is a byproduct of protein metabolism. While some of it is passively reabsorbed in the kidneys, it is mostly excreted in the urine to eliminate excess nitrogen from the body.

Additional Knowledge:

• Glucose is actively reabsorbed in the proximal convoluted tubule by sodium-glucose cotransporters. In a healthy kidney, glucose should not be found in the urine under normal conditions.
• Amino acids are also reabsorbed in the proximal convoluted tubule, ensuring that essential building blocks for protein synthesis are retained in the body.
• Various salts, such as sodium, potassium, and chloride, are reabsorbed in different sections of the renal tubules, especially in the proximal tubule, loop of Henle, and distal convoluted tubule.