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Intestinal motility
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Intestinal motility is the set of movements the intestine uses to handle what is inside it, and they come in two kinds. Peristalsis pushes the contents forward. Segmentation does not push them: it mixes them. The two together are what allow the intestine to absorb water and nutrients.
The one setting the pace is not the brain. Between the two muscle layers of the wall, the circular layer on the inside and the longitudinal layer on the outside, there is a network of nerves called the myenteric plexus, and that is where the interstitial cells of Cajal live. Those cells are the pacemaker of the digestive tract: they generate slow waves, depolarizations that spread through the muscle.
The bolus moves along like this. When the bolus, the portion of food, is passing through a segment of intestine, the circular layer just behind it contracts and the one just ahead of it relaxes. It is like squeezing a tube behind the contents while the way ahead opens up. With each wave the bolus advances a few centimeters, and the cycle starts over.
In brief
The digestive tract has two movements: peristalsis, which propels the contents, and segmentation, which mixes them; together they allow water and nutrients to be absorbed.
The myenteric plexus, between the circular and longitudinal muscle layers, houses the interstitial cells of Cajal, the pacemaker that generates slow waves.
With the bolus in a segment, the circular layer behind it contracts and the layer ahead relaxes, and the bolus advances a few centimeters with each wave.
It is like squeezing a tube behind the contents while the way ahead opens up.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingPhysiology, Peristalsis, StatPearlsPublished
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