Question

The urea cannot pass out from the tubular fluid while flowing through the renal tubule in the following parts EXCEPT:

• A. Ascending limb
• B. DCT
• C. Deep medullary region of collecting duct.
• D. The cortical portion of the collecting duct.

Hint:

Only the deep medullary collecting duct is permeable to urea.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept
Urea permeability differs among parts of the renal tubule.

Step 2: Check each segment
The thick ascending limb, the DCT and the cortical collecting duct are impermeable to urea, so urea stays in the tubular fluid there.
The inner medullary collecting duct is permeable, so urea diffuses out into the medullary interstitium.

Step 3: Role of this urea
The urea adds to the high osmolarity of the inner medulla, which helps to form concentrated urine. So this is the exception.

Final Answer:
The exception is the deep medullary region of the collecting duct. \[ \boxed{\text{(C) }\text{Deep medullary region of collecting duct.}} \]