**Question:** Impaired function of aquaporin results in

A. Decreased water permeability
B. Increased water permeability
C. Altered ion transport
D. Disturbed blood flow regulation

**Core Concept:**
Aquaporins are a group of membrane proteins that facilitate the passive transport of water across cell membranes. They play a crucial role in maintaining the water balance in various physiological processes, including osmoregulation, cell volume control, and fetal lung fluid clearance. Impaired aquaporin function can lead to various consequences depending on the specific aquaporin and cellular context.

**Why the Correct Answer is Right:**
Aquaporin 1 (AQP1) is primarily involved in the regulation of red blood cell volume and the formation of the renal collecting duct. Impaired AQP1 function can result in decreased water permeability, leading to polyuria (excessive urine production) and polydipsia (increased thirst).

**Why Each Wrong Option is Incorrect:**

B. Increased water permeability (Option B) is incorrect because it refers to the normal function of aquaporins. Impaired AQP1 function leads to decreased water permeability, not increased.

C. Altered ion transport (Option C) is not the correct answer, as aquaporins primarily facilitate water transport, not ion transport.

D. Disturbed blood flow regulation (Option D) is unrelated to the specific function of AQP1. Impaired AQP1 function primarily affects water transport rather than blood flow regulation.

**Why the Correct Answer is Right:**
Aquaporin 1 (AQP1) has a crucial role in regulating the water permeability of red blood cells and renal collecting duct cells. Impaired AQP1 function results in decreased water permeability, leading to excessive water loss and subsequent compensatory mechanisms such as increased urine production (polyuria) and thirst (polydipsia). This illustrates the importance of AQP1 in maintaining fluid homeostasis within the body.