Which of the following components of blood does not enter the nephron?

Options

A. Plasma proteins
B. Glucose
C. Sodium `(Na^(+))` ions
D. Urea

Explanation

To determine which component of blood does not enter the nephron, we will analyze each of the provided options: plasma protein, glucose, sodium ions, and urea.

### Step-by-Step Solution:

1. **Understanding Nephron Function**:
- The nephron is the functional unit of the kidney, responsible for filtering blood and forming urine. The filtration occurs in the glomerulus, where blood components are separated based on their size.

2. **Analyzing Each Component**:
- **Urea**:
- Urea is a small molecule produced from the breakdown of proteins. Due to its small size, it easily passes through the filtration barrier of the nephron and enters the nephron.
- **Sodium Ions**:
- Sodium ions are also small and are crucial for maintaining the body's ionic balance. They can easily enter the nephron through the filtration process.
- **Glucose**:
- Glucose is a simple sugar that is soluble in blood. It is filtered through the nephron and is reabsorbed back into the bloodstream, but it does enter the nephron during filtration.
- **Plasma Proteins**:
- Plasma proteins, such as albumin, are much larger molecules (with a size greater than 100 kDa). Due to their size, they do not pass through the filtration barrier of the nephron and remain in circulation.

3. **Conclusion**:
- Among the options provided, **plasma proteins** do not enter the nephron due to their large size, while urea, sodium ions, and glucose do enter the nephron.

### Final Answer:
**Plasma proteins do not enter the nephron.**

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