The human digestive system has two functions:
Regions of the digestive system are adapted to the digestion and absorption of food:
|Mouth||Begins the digestion of carbohydrates|
|Stomach||Begins the digestion of protein; small molecules such as alcohol absorbed|
|Small intestine - Duodenum||Continues the digestion of carbohydrate and protein; begins the digestion of lipids|
|Small intestine - Ileum||Completes the digestion of carbohydrates and proteins into single sugars and amino acids; absorption of single sugars, amino acids and fatty acids and glycerol|
|Large intestine||Absorption of water; egestion of undigested food|
The surface of the small intestine wall is folded, and has projections called villi.
The epithelial cells that cover each villus themselves have projections called microvilli.
These all increase the surface area over which digested food – now simple molecules – is absorbed.
Most of the digested food passes through the epithelial cells of the gut wall and is carried by blood to the liver. Digested lipids pass through the gut wall and enter the lacteals.