Which of theses statements about proximal convoluted tubule is/are true?
I. it is lined by simple columnar brush border epithelium which increases the surface area for reabsorption.
II Nearly all of the essential nutrients and 70%-80% of electrolytes and water are reabsorbed by this segment.
III. It selectively secretes hydrogen ions, ammonia and potassium ions into the filtrate.
IV. It is the most convoluted part of the nephron and is present in the medullary region of the kidney.

Options

A. I and IV
B. I, II and III
C. II and III
D. I, II, III and IV

Answer

To determine which statements about the proximal convoluted tubule (PCT) are true, let's analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement I**: "It is lined by simple columnar brush border epithelium which increases the surface area for reabsorption."
- **Analysis**: This statement is true. The PCT is indeed lined with simple columnar epithelium that has microvilli (brush border), which significantly increases the surface area for reabsorption of substances from the filtrate.

2. **Statement II**: "Nearly all of the essential nutrients and 70%-80% of electrolytes and water are reabsorbed by this segment."
- **Analysis**: This statement is also true. The PCT reabsorbs approximately 65-70% of water and a significant portion of essential nutrients and electrolytes from the filtrate.

3. **Statement III**: "It selectively secretes hydrogen ions, ammonia and potassium ions into the filtrate."
- **Analysis**: This statement is true as well. The PCT plays a role in the secretion of hydrogen ions, ammonia, and potassium ions, which helps in maintaining the body's pH and ionic balance.

4. **Statement IV**: "It is the most convoluted part of the nephron and is present in the medullary region of the kidney."
- **Analysis**: This statement is false. While the PCT is convoluted, it is not the most convoluted part of the nephron; that title goes to the distal convoluted tubule (DCT). Additionally, the PCT is located in the renal cortex, not the medullary region.

### Conclusion:
Based on the analysis, the true statements about the proximal convoluted tubule are:
- **I, II, and III** are true.
- **IV** is false.

Thus, the correct answer is that statements I, II, and III are true.