Pediatric Lactase Deficiency — Mechanism

10 single-best-answer MCQs · Select one option each · Tap to check

Lactose

↓ Brush-border lactase

Osmosis + fermentation

Brush borderOsmotic diarrheaBacterial fermentationPrimary vs secondaryHydrogen breath test

1. Lactase is normally located predominantly at which site?

Lactase is a brush-border disaccharidase concentrated near mature enterocytes at villous tips.

2. Lactase normally hydrolyses lactose into:

Lactose is split into glucose and galactose before absorption.

3. The immediate cause of watery diarrhea after lactose ingestion is:

Unabsorbed lactose raises luminal osmotic load, retaining water and producing osmotic diarrhea.

4. Abdominal bloating and flatus mainly result from:

Colonic bacteria ferment lactose to hydrogen, carbon dioxide, methane and short-chain acids.

5. Acidic stools in lactase deficiency are explained by formation of:

Bacterial fermentation generates lactic and short-chain fatty acids, lowering stool pH.

6. Primary lactase non-persistence is due to:

Lactase expression physiologically declines after weaning in genetically susceptible populations.

7. Secondary lactase deficiency follows mucosal injury because lactase is:

Villous-tip enzymes are lost early in gastroenteritis, celiac disease and other mucosal injuries.

8. Congenital lactase deficiency most often reflects:

Rare congenital lactase deficiency is an autosomal-recessive disorder caused by pathogenic variants in LCT.

9. The hydrogen breath test becomes positive because:

Fermentation-derived hydrogen is absorbed into blood and exhaled, producing the breath-hydrogen rise.

10. Why does diarrhea improve during fasting?

Carbohydrate-induced osmotic diarrhea falls when the unabsorbed solute is withdrawn.

Lactase Mechanism MCQs