During urine formation, which of the following process helps in maintaining osmotic pressure in the uriniferous tubule?

Options

A. Active `Na^(+)` absorption , followed by absorption of `Cl^(-)`
B. Active `Cl^(+)` absorption , followed by absorption of `Na^(+)`
C. Active secretion of `Na^(+)` into efferent arteriole followed by absorption of `Cl^(-)` into efferent renal arteriole
D. Active secretion of `Cl^(-)` and absorption of `N^(+)a` into efferent renal arteriole

Answer

To solve the question regarding the process that helps maintain osmotic pressure in the uriniferous tubule during urine formation, let's break it down step by step:

### Step 1: Understanding the Uriniferous Tubule
The uriniferous tubule is the functional unit of the kidney, which consists of the nephron. It plays a crucial role in the formation of urine through processes such as filtration, reabsorption, and secretion.

### Step 2: Identifying Key Processes in Urine Formation
During urine formation, three main processes occur:
1. **Filtration**: Blood is filtered in the glomerulus.
2. **Reabsorption**: Essential substances like water, sodium, and chloride are reabsorbed back into the bloodstream.
3. **Secretion**: Waste products are secreted into the tubule.

### Step 3: Role of Sodium and Chloride
Sodium (Na+) and chloride (Cl-) ions are critical in maintaining osmotic pressure:
- **Sodium Reabsorption**: About 70% of sodium is reabsorbed in the proximal convoluted tubule (PCT). This reabsorption is crucial for maintaining osmotic pressure because it influences water reabsorption.
- **Chloride Reabsorption**: Chloride ions are also reabsorbed, which helps balance the osmotic pressure created by sodium.

### Step 4: Analyzing the Options
Now, let's analyze the provided options:
1. **Active Na+ absorption followed by Cl- absorption**: This is correct as sodium is actively reabsorbed, which is followed by the reabsorption of chloride.
2. **Active Cl- absorption**: This is incorrect since sodium is absorbed first.
3. **Active secretion of Na+**: This is incorrect; sodium is reabsorbed, not secreted.
4. **Secretion of Cl-**: This is also incorrect; chloride is reabsorbed, not secreted.

### Step 5: Conclusion
The correct answer is the first option: **Active Na+ absorption followed by Cl- absorption**. This process is essential for maintaining osmotic pressure in the uriniferous tubule.

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