Peristalsis sim
Contract the circular muscles behind a bolus and the longitudinal muscles in front of it, segment by segment, then turn the oesophagus upright, lying down or upside down and switch gravity off: the food still arrives at the same speed.
Nutrition in humans: peristalsis · covers the O-Level, IGCSE, GCSE topic
What the sim shows
Peristalsis is a wave of muscle contraction that pushes food along the gut. The wall has two muscle layers that work as an antagonistic pair: when one contracts, the other relaxes. Behind the bolus the circular muscles contract and the longitudinal muscles relax, so the tube there becomes narrower and longer and squeezes the bolus forward. In front of it the longitudinal muscles contract and the circular muscles relax, so the tube there becomes wider and shorter and makes room. Mucus from the lining helps it slide. The wave carries the bolus at about 3 cm/s whatever position you are in, so you can swallow lying down or upside down, and astronauts can swallow in orbit: gravity is not what moves food. The numbers: a typical squeeze of 10.7 kPa (about 80 mmHg; normal values 30–180 mmHg) on a bolus 2 cm wide pushes with about 3.4 N (an upper estimate: squeeze pressure × the bolus's cross-section, ignoring the small pressure in front), while a 10 g bolus weighs 0.10 N (g = 10 N/kg): the push is about 34 times the weight. In real life gravity helps a little when you are upright, but the muscles do the work. Each step moves the bolus one 2.5 cm segment in 0.83 s; time moves only when a step happens. Model limits: the tube is cut into 10 segments, and one step moves the bolus one segment; in the model the relaxed tube's grip on a solid bolus (0.5 N, illustrative) holds it still when the muscles are relaxed; liquids can run down an upright oesophagus faster than the wave, helped by gravity, so this model is for a solid bolus.
- Muscle colour: pale = relaxed, deep red = contracting
- Pivot: turn the tube upright, lying down or upside down
- Plumb line: the way gravity pulls (it floats when gravity is off)
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