Laid flat, the absorptive surface of the small intestine covers some 30 to 40 m², thanks to three tiers of amplification: mucosal folds, then villi, then microvilli. A course of antibiotics sweeps away friendly and hostile bacteria alike as diversity collapses; in coeliac disease gluten drives an immune attack that erodes the villi, leaving a flat lining that lets nutrients slip past. The gut also wires straight to the head: roughly 500 million enteric neurons talk to the brain along the vagus nerve.
Laid flat, the absorptive surface of the small intestine covers some 30 to 40 m², thanks to three tiers of amplification: mucosal folds, then villi, then microvilli. A course of antibiotics sweeps away friendly and hostile bacteria alike as diversity collapses; in coeliac disease gluten drives an immune attack that erodes the villi, leaving a flat lining that lets nutrients slip past. The gut also wires straight to the head: roughly 500 million enteric neurons talk to the brain along the vagus nerve.
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