What are capillaries ? Write their function

Explanation

### Step-by-Step Solution:

1. **Definition of Capillaries**:
- Capillaries are the smallest blood vessels in the body. They are microscopic in size and connect arterioles (small arteries) to venules (small veins).

2. **Structure of Capillaries**:
- The walls of capillaries are extremely thin, consisting of only a single layer of endothelial cells. This thinness facilitates the exchange of materials.

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