# What are capillaries?

The the smallest blood vessels is called the capillaries. Gray's Anatomy (1918) describes it as the smallest blood vessels in the body.

## What it means

- The smallest blood vessels in the body.
- Their walls are only a single cell thick.
- The site where oxygen, nutrients, and waste products are exchanged between blood and tissue.

## Action steps

1. Form dense networks (capillary beds) within every tissue.
2. Connect the smallest arteries (arterioles) to the smallest veins (venules).
3. Nearly every cell in the body lies within a fraction of a millimeter of a capillary.

## Sources

- [Gray's Anatomy of the Human Body (1918)](https://www.bartleby.com/107/)

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