Expansion
Iron in the duodenum, folate in the jejunum, B12 and bile salts in the terminal ileum
Expansion
| Site | Absorbed |
|---|---|
| Duodenum | Iron, calcium, magnesium, most fat-soluble vitamins |
| Jejunum | Folate, most sugars, amino acids, fats and water-soluble vitamins |
| Ileum | Continued absorption of most nutrients |
| Terminal ileum | Vitamin B12 (with intrinsic factor) and bile salts |
| Colon | Water, electrolytes, short-chain fatty acids, vitamin K |
The two ends are the ones that matter clinically because they are site-specific and irreplaceable:
- Duodenal disease (coeliac disease, bypass surgery) causes iron deficiency
- Terminal ileal disease or resection causes B12 deficiency and bile salt diarrhoea
Everything in between has a large functional reserve, which is why the jejunum can be resected extensively with relatively little consequence.