Final answer:
The small intestine's interior is highly folded with structures called villi and microvilli, increasing the surface area for absorbing nutrients. Villi absorb the products of digestion and transport them to the circulatory and lymphatic systems. The three segments of the small intestine, the duodenum, jejunum, and ileum, each have specific roles in the digestion and absorption process.
Step-by-step explanation:
The interior of the small intestine is designed to maximize nutrient absorption. It has a highly folded inner wall, looking much like corrugations of cardboard, and is covered with fingerlike projections known as villi. These villi are further covered with microscopic projections called microvilli, which resemble little brushes. The villi and microvilli increase the surface area for absorption up to 600 times compared to a smooth surface, thereby significantly enhancing the intestine's ability to absorb nutrients. This structured and bumpy appearance contributes to the small intestine's ability to efficiently absorb digested nutrients and transport them to the bloodstream or the lymphatic system.
The small intestine is responsible for the completion of digestion of proteins, fats, and carbohydrates. Here, enzymes such as trypsin digest proteins, lipase digests fats, and maltase breaks down specific sugars. The increased surface area provided by the villi and microvilli ensures that the small intestine is highly effective at absorbing these nutrients once they are broken down into smaller molecules. The duodenum, the jejunum, and the ileum are the three parts of the small intestine, each playing a crucial role in digestion and absorption.