Small intestine nutrient absorption

Small intestine nutrient absorption" refers to the physiological process by which digested nutrients—including carbohydrates, proteins, fats, vitamins, minerals, and water—are absorbed from the lumen of the small intestine into the blood or lymphatic circulation. This process is facilitated by specialized structures such as villi and microvilli that greatly increase surface area for efficient uptake. Different regions of the small intestine are responsible for absorbing specific nutrients; for example, iron is absorbed in the duodenum while vitamin B12 and bile salts are absorbed in the terminal ileum. The majority of nutrient absorption occurs in the jejunum. Absorption mechanisms include passive diffusion (for water and lipids), active transport (for sodium bicarbonate), co-transport with glucose or amino acids, and facilitated diffusion (for fructose). The process is essential for providing energy and building blocks to body tissues[1][2][4][6]. Note on target status: "Small intestine nutrient absorption" describes a physiological function rather than a discrete molecular target such as a receptor, enzyme, transporter, or channel. Therefore it is not considered a therapeutic target itself but rather an outcome mediated by many different molecular targets within intestinal epithelial cells[1][5].