Tubular secretion adds to the glomerular filtrate

Options

A. Urea
B. Uric acid
C. Ammonia
D. All the above

Answer

To answer the question "Tubular secretion adds to the glomerular filtrate," we will go through the process of urine formation in the kidneys and identify what substances are involved in tubular secretion.

### Step-by-Step Solution:

1. **Understanding Urine Formation**:
- Urine formation in the kidneys occurs through three main processes: glomerular filtration, tubular reabsorption, and tubular secretion.

2. **Glomerular Filtration**:
- In the first step, blood is filtered in the glomerulus, where water, ions, and small molecules pass through the glomerular membrane into the Bowman’s capsule, forming the glomerular filtrate.

3. **Tubular Reabsorption**:
- After filtration, the renal tubules reabsorb essential substances (like glucose, amino acids, and certain ions) back into the bloodstream, which is not part of tubular secretion.

4. **Tubular Secretion**:
- Tubular secretion is the process where certain substances are actively transported from the blood in the peritubular capillaries into the tubular fluid. This process helps to eliminate waste products and maintain pH balance.

5. **Substances Involved in Tubular Secretion**:
- The substances that are typically secreted into the tubular fluid include:
- **Urea**: A waste product formed from protein metabolism.
- **Uric Acid**: A product of purine metabolism.
- **Ammonia**: A byproduct of amino acid metabolism.

6. **Conclusion**:
- Since tubular secretion adds urea, uric acid, and ammonia to the glomerular filtrate, the correct answer to the question is "all the above."

### Final Answer:
**All the above (urea, uric acid, ammonia)** are added to the glomerular filtrate through tubular secretion.

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