The human digestive system
The human Organ system involved in breaking food down so that it can be absorbed into the bloodstream. has two functions:
- breaks down complex food substances
- provides the very large surface area for maximum absorption of food
The structure of the digestive system
Regions of the digestive system are adapted to the digestion and absorption of food:
Digestion
| Region | Function |
| 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 |
| Region | Mouth |
|---|---|
| Function | Begins the digestion of carbohydrates |
| Region | Stomach |
|---|---|
| Function | Begins the digestion of protein; small molecules such as alcohol absorbed |
| Region | Small intestine - duodenum |
|---|---|
| Function | Continues the digestion of carbohydrate and protein; begins the digestion of lipids |
| Region | Small intestine - ileum |
|---|---|
| Function | Completes the digestion of carbohydrates and proteins into single sugars and amino acids; absorption of single sugars, amino acids and fatty acids and glycerol |
| Region | Large intestine |
|---|---|
| Function | Absorption of water; egestion of undigested food |
Digestive A protein which catalyses or speeds up a chemical reaction. are used to break down food in the The digestive system. It is involved in breaking down complex food molecules and the absorption of simple food molecules into the bloodstream. into small, Able to dissolve in solvent. For example, sugar is soluble in water because it dissolves to form sugar solution. molecules that can be absorbed through the gut wall.
Absorption
The surface of the small intestine wall is folded, and has projections called Finger-like projections in the small intestine that provide a large surface area for the absorption of food.. Villi is the plural of villus.
The A cell that forms part of an epithelium. that cover each villus themselves have projections called Projections from the surface of an epithelial cell of the small intestine wall..
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.
The lacteals in each villus join together into larger vessels. Then all the digested lipids pass through a duct into the bloodstream.