Phase and nature of malabsorptive defect | Example |
Luminal phase | |
A. Substrate hydrolysis | |
1. Digestive enzyme deficiency | Chronic pancreatitis |
2. Digestive enzyme inactivation | Zollinger-Ellison syndrome |
3. Dyssynchrony of enzyme release, inadequate mixing | Post Billroth II procedure |
B. Fat solubilization | |
1. Diminished bile salt synthesis | Cirrhosis |
2. Impaired bile secretion | Chronic cholestasis |
3. Bile salt de-conjugation | Bacterial overgrowth |
4. Increased bile salt loss | Ileal disease or resection |
C. Luminal availability of specific nutrients | |
1. Diminished gastric acid | Atrophic gastritis - vitamin B12 |
2. Diminished intrinsic factor | Pernicious anemia - vitamin B12 |
3. Bacterial consumption of nutrients | Bacterial overgrowth - vitamin B12 |
Mucosal (absorptive) phase | |
A. Brush border hydrolysis* | |
1. Congenital disaccharidase defect | Sucrase-isomaltase deficiency |
2. Acquired disaccharidase defect | Lactase deficiency |
B. Epithelial transport | |
1. Nutrient-specific defects in transport | Hartnup's disease |
2. Global defects in transport | Celiac sprue |
Postabsorptive, processing phase | |
A. Enterocyte processing | Abetalipoproteinemia |
B. Lymphatic | Intestinal lymphangiectasia |
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