Question

Main function of kidney is:

• A. Passive absorption
• B. Ultrafiltration
• C. Selective reabsorption
• D. All of the above

Answer 1

The correct option is D All of the above

• Ultrafiltration, selective reabsorption, and passive absorption all occur in the kidneys during the process of urine formation.
• Ultrafiltration means the diffusion of blood, including plasma to the nephron to be filtered. Red blood cells and plasma proteins cannot pass through the ultrafiltration membrane because their size is too big.
• Reabsorption includes active and passive transport. Water is absorbed by osmosis or via aquaporin. Ions (e.g.: Na+) are reabsorbed by active transport while glucose, amino acids, and small hydrophobic molecules can be reabsorbed by diffusion or facilitated diffusion. The process of reabsorption occurs in the renal tubule.

So, the correct answer is option D.