What does haemodialysis do?

Explanation

### Step-by-Step Solution:

1. **Understanding the Context**: Hemodialysis is a medical procedure used when the kidneys are not functioning properly. It is essential for patients with kidney failure or severe kidney dysfunction.

2. **Function of Hemodialysis**: The primary purpose of hemodialysis is to filter waste products, excess salts, and fluids from the blood, mimicking the natural function of healthy kidneys.

3. **The Machine Used**: The procedure involves a machine known as a hemodialyzer, which acts as an artificial kidney. This machine is responsible for the filtration process.

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