The selective secretion of hydrogen ion, ammonia and potassium into the filtrate takes place mainly in

Options

A. Proximal convoluted tubule
B. Henle's loop
C. Distal convoluted tubules
D. Collecting duct

Answer

To solve the question regarding the selective secretion of hydrogen ions, ammonia, and potassium into the filtrate, we need to analyze the functions of different parts of the nephron.

### Step-by-Step Solution:

1. **Understanding the Nephron Structure**:
- The nephron is the functional unit of the kidney and consists of several parts: the glomerulus, Bowman's capsule, proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct.

2. **Identifying the Function of Each Part**:
- **Proximal Convoluted Tubule (PCT)**: This is where the majority of reabsorption occurs (about 70-80% of water and electrolytes). It is also responsible for the secretion of substances such as hydrogen ions, ammonia, and potassium into the filtrate.
- **Loop of Henle**: This structure is primarily involved in the concentration of urine. The descending limb is permeable to water but not to electrolytes, while the ascending limb is impermeable to water but allows the passage of electrolytes.
- **Distal Convoluted Tubule (DCT)**: This part also contributes to the secretion of hydrogen ions and potassium ions but is not the primary site for the secretion of these ions.
- **Collecting Duct**: This section helps in the regulation of water and electrolyte balance but is not the main site for the selective secretion of hydrogen ions, ammonia, and potassium.

3. **Conclusion**:
- The main site for the selective secretion of hydrogen ions, ammonia, and potassium into the filtrate is the **Proximal Convoluted Tubule (PCT)**.

### Final Answer:
The selective secretion of hydrogen ions, ammonia, and potassium into the filtrate takes place mainly in the **Proximal Convoluted Tubule (PCT)**.