Intestinal brush border. Transmission electron micrograph (TEM) of intestinal absorptive cells sectioned horizontally at their apex to show the surface microvilli (round). Microvilli are slender finger-like extensions of the intestinal cell that serve to greatly increase the surface area for absorption of nutrients from the lumen of the gastrointestinal tract. The brush borders of the intestinal lining are the site of terminal carbohydrate digestion. The microvilli have enzymes for this final part of digestion anchored into their apical plasma membrane as integral membrane proteins. These enzymes are found near to the transporters that will then allow absorption of the digested nutrients.