Final answer:
Microvilli are most abundant in the small intestine, especially the jejunum, where they significantly increase the surface area for efficient nutrient absorption.
Step-by-step explanation:
Microvilli are the longest and most abundant in the small intestine, particularly in the jejunum segment. These tiny protrusions greatly increase the surface area available for absorption, which enhances the small intestine's ability to absorb nutrients efficiently.
Each microvillus, approximately 1 µm in length, contains a core of actin microfilaments and is covered in plasma membrane. This configuration contributes to forming what is known as the brush border, which is densely packed with these structures. Microvilli contain enzymes that complete the digestion of carbohydrates and proteins, facilitating nutrient assimilation into the bloodstream. An estimated 200 million microvilli per square millimeter can be found in the small intestine, optimizing the digestive system's capacity to process and absorb dietary nutrients.