A fluorescent dye is utilized to 'tag' antidiuretic hormone receptors. The greatest concentration of dye is expected in which of the following structures?

Options

A. Proximal convoluted tubule
B. Renal capillaries
C. Loop of Henle
D. Collecting duct

Answer

To solve the question regarding the expected concentration of a fluorescent dye used to tag antidiuretic hormone (ADH) receptors, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Role of Antidiuretic Hormone (ADH)**:
- ADH, also known as vasopressin, plays a crucial role in regulating water balance in the body. It primarily acts on the kidneys to promote water reabsorption.

2. **Identify the Structures of the Nephron**:
- The nephron is the functional unit of the kidney and consists of several parts:
- Glomerulus
- Bowman’s capsule
- Proximal convoluted tubule (PCT)
- Loop of Henle (with descending and ascending limbs)
- Distal convoluted tubule (DCT)
- Collecting duct

3. **Locate the ADH Receptors**:
- ADH receptors are primarily located in the collecting duct of the nephron. This is where ADH exerts its effect by increasing the permeability of the duct to water, allowing for more water reabsorption into the bloodstream.

4. **Determine Where the Fluorescent Dye Would Accumulate**:
- Since the fluorescent dye is used to tag ADH receptors, and these receptors are concentrated in the collecting duct, we can conclude that the greatest concentration of the dye will also be found in the collecting duct.

5. **Select the Correct Answer**:
- Based on the information gathered, the structure where the greatest concentration of the fluorescent dye is expected is the **collecting duct**.

### Final Answer:
The greatest concentration of the fluorescent dye is expected in the **collecting duct**.

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