Carbohydrate digestion - disaccharidase products (lactose, sucrose)
Core concept
- Only MONOSACCHARIDES are absorbed - all dietary carbohydrate must be reduced to glucose, galactose or fructose
- Two stages
- Luminal: salivary and pancreatic alpha-amylase -> starch to maltose, maltotriose, alpha-limit dextrins
- Brush border: membrane-bound disaccharidases on the microvilli of the small intestinal enterocyte
| Disaccharidase | Substrate | Products |
|---|---|---|
| Lactase | Lactose | Glucose + GALACTOSE |
| Sucrase | Sucrose | Glucose + FRUCTOSE |
| Maltase / glucoamylase | Maltose, maltotriose | Glucose + glucose |
| Isomaltase (alpha-dextrinase) | Alpha-1,6 limit dextrins | Glucose |
| Trehalase | Trehalose (mushrooms) | Glucose + glucose |
- Transport across the enterocyte
- Glucose and galactose -> SGLT1 (apical, Na-coupled secondary active transport)
- Fructose -> GLUT5 (apical, facilitated - no sodium, no energy)
- All three exit basolaterally via GLUT2
3 more sections, plus exam facts
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