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 **incorrect**. The proximal convoluted tubule is actually lined by simple cuboidal epithelium with a brush border. The brush border does indeed increase the surface area for reabsorption, but the type of epithelium is incorrectly stated as columnar.

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 **correct**. The PCT is responsible for the reabsorption of approximately 65-70% of water and electrolytes, as well as nearly all essential nutrients such as glucose and amino acids.

3. **Statement III**: "It selectively secretes hydrogen ions, ammonia, and potassium ions into the filtrate."
- **Analysis**: This statement is **correct**. The PCT does have a role in the selective secretion of substances such as hydrogen ions, ammonia, and potassium ions into the filtrate, which helps in maintaining acid-base balance and electrolyte levels.

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 **incorrect**. While the PCT is indeed convoluted, it is not located in the medullary region; it is found in the renal cortex. The most convoluted part of the nephron is actually the distal convoluted tubule (DCT).

### Conclusion:
- The true statements about the proximal convoluted tubule are **II and III**. Therefore, the correct answer is that statements II and III are true.