The small intestine is the principal site for the chemical digestion and subsequent absorption of nutrients. Functionally, it is divided into three segments: the duodenum, which receives bile and digestive enzymes from the liver and pancreas; the jejunum, where the majority of nutrient absorption occurs; and the ileum, which absorbs specific substances, including B12 and bile salts. Its inner lining is highly folded and possesses microscopic projections called villi, which are themselves covered in microvilli. This extensive surface area maximization is crucial for efficiently absorbing complex molecules such as carbohydrates, proteins, and fats into the bloodstream and lymphatic system for systemic use.