The blood in the artificial kidney flows through channels or tubes bounded by `"________"`

Explanation

**Step-by-Step Solution:**

1. **Understanding the Context**: The question pertains to the function of an artificial kidney, also known as a dialyzer, which is used in the process of hemodialysis to treat kidney failure.

2. **Identifying the Components**: In an artificial kidney, blood flows through channels or tubes. The key component that separates the blood from the dialysate (the fluid used in dialysis) is a membrane.

3. **Recognizing the Type of Membrane**: The membrane used in artificial kidneys is a semi-permeable membrane. This type of membrane allows certain substances to pass through while blocking others.

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