More specifically, it's found on the apical surface (the surface facing the lumen) of the epithelial cells that line the small intestine.

Here's why it's important:

* Increased Surface Area: The brush border is made up of microscopic, finger-like projections called microvilli. These microvilli greatly increase the surface area of the small intestine, which is crucial for efficient absorption of nutrients.

* Digestive Enzymes: The brush border also contains enzymes that play a role in the final stages of digestion, breaking down carbohydrates, proteins, and fats into smaller molecules that can be absorbed by the body.

Let me know if you have any more questions about the brush border or the small intestine!