Absorption in Small Intestine

Nutrient absorption in the small intestine occurs through several mechanisms:

1. Villi and microvilli: Increase the surface area for absorption
2. Simple diffusion: For small, non-polar molecules like oxygen and carbon dioxide
3. Facilitated diffusion: For larger molecules like glucose and amino acids
4. Active transport: For ions and some nutrients against concentration gradients
5. Endocytosis: For large molecules and particles

Absorbed nutrients enter the bloodstream through capillaries in the villi or are transported to the lymphatic system (for fats). The absorbed nutrients are then distributed throughout the body for energy production and cellular functions.