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How are nutrients absorbed after food is digested?

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After food is digested, nutrients are absorbed primarily in the small intestine, where the surface area is vastly increased by villi—slender, vascular projections covered in even smaller microvilli.

Nutrients cross the intestinal membrane into the body through four primary mechanisms:
* Active transport: A carrier-mediated process that moves substances against a chemical or electrical gradient, requiring energy.1
* Passive diffusion: The movement of substances along a concentration gradient without the need for energy or carriers.1
* Facilitated diffusion: A carrier-mediated process that requires no energy to move substances across the membrane.1
* Endocytosis: The process by which material is engulfed into the cell interior.1

Once absorbed, proteins and carbohydrates typically enter the blood vessels within the villi, while emulsified fats are taken up by lymphatic capillaries called lacteals. These nutrients are then transported through the blood to tissues throughout the body, where they pass through capillary walls to reach the cells that require them.234