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How are nutrients absorbed from the small intestine into the bloodstream?

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Diagram of the human digestive system viewed from the front, showing and labeling organs including the mouth, teeth, tongue, salivary glands, pharynx, esophagus, liver, stomach, gallbladder, pancreas, large intestine, small intestine, appendix, rectum, and anus. — digestion The human digestive system as seen from the front.

Nutrients are absorbed from the small intestine into the bloodstream through the villi, which are small, slender projections that significantly increase the surface area of the intestinal lining. Absorption occurs via four primary mechanisms: active transport, passive diffusion, facilitated diffusion, and endocytosis.12

Proteins and carbohydrates are typically transported into the blood vessels located within the core of each villus. Once absorbed, these nutrients enter the portal vein, which carries blood from the intestines directly to the liver for processing and distribution.13

Fats follow a different pathway. After being processed into chylomicrons within the intestinal cells, they are generally absorbed into the lymphatic system via specialized vessels called lacteals. However, medium-chain fatty acids are water-soluble and can pass directly into the capillary tributaries of the portal vein to reach the liver. The swaying and contracting motions of the villi help enhance this overall flow of blood and lymph, facilitating efficient nutrient uptake.41