What is pleural fluid? Why is it important?

Explanation

### Step-by-Step Solution

1. **Definition of Pleural Fluid**:
- Pleural fluid is a watery substance that is found between two membranes known as the pleural membranes. These membranes surround the lungs.

2. **Location of Pleural Fluid**:
- The pleural fluid is located in the pleural cavity, which is the space between the two pleural membranes (the visceral pleura that covers the lungs and the parietal pleura that lines the chest wall).

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