Final answer:
The small intestine is divided into three main regions known as the duodenum, jejunum, and ileum, which play crucial roles in digestion and nutrient absorption thanks to their folded mucosal lining equipped with villi and microvilli.
Step-by-step explanation:
The small intestine consists of three major regions: a) Duodenum, jejunum, ileum. The duodenum is the first part where initial digestion occurs, the jejunum is a lengthy middle section, and the ileum is the final part leading towards the large intestine. These regions are essential for the digestion of food and absorption of nutrients due to their specialized structures. The inner lining of these regions features villi and microvilli, which drastically increase the surface area for absorption.
The jejunum, approximately 0.9 meters (3 feet) long, is so named because it was often found empty after death, according to ancient observers. The small intestine's mucosal lining is highly adapted to maximize nutrient absorption, equipped with circular folds, villi, and microvilli, containing brush border enzymes that aid in the complete digestion of nutrients.