As we talk about the small intestine, I think it's important to remember that we're talking about a 6 to 7 meter long tube. Something like 20 feet, and we need to move the chyme inside this tube. Now to do that, we are talking about motility in the small intestine. Now we're going to start out just by saying that it typically takes chyme about 3 to 6 hours to move through the small intestine. And that number, 3 to 6 hours, initially kind of sounds like a lot to me. But if I think of a coiled tube 20 feet long, the diameter of a sausage, and I need to move a slop through it using only muscle contraction, it sounds about right.
The way this works is a process called peristalsis, and peristalsis is a wave of muscle contraction. That wave of muscle contraction pushes chyme through the GI tract, starting at the esophagus all the way through to the large intestine. And the way this works, importantly, is that it uses both the circular and the longitudinal muscle layers of the muscularis externa. So, we can see this in our image here. We have this chyme here, and we can see both layers of this muscularis externa kind of squeezing in like a ring squeezing down. As it squeezes just kind of behind this chyme, that pushes that chyme forward. And then that squeeze kind of moves along in a wave, and so does the chyme get pushed forward, so on and so on all the way through. Just like if you had a tube of toothpaste and the toothpaste was all at the back of the tube, you squeeze in the back and just squeeze along and push it to the other end.
Now that's in contrast to segmentation. Segmentation is going to be non-adjacent contraction. So just kind of squeezing almost randomly back and forth. Now segmentation aids in mechanical digestion. Mechanical digestion, remember, that's sort of physically breaking up the food particles, and it's also going to mix in the enzymes into that chyme to really help with chemical digestion and make that chemical digestion more efficient. Now, different from peristalsis, this uses the inner circular layer of the muscularis externa only. So, if we look at this, we have the small intestine, and we have sort of blue and yellow bits of chyme, sort of showing how the chyme is separate from each other, and we can see just this inner layer squeezing in different places.
And as it squeezes in, this kind sort of squishes out both sides. And then as you do that again somewhere else, well, now it squeezes in and it squishes out in a different way down here. And as you keep sort of squishing back and forth, we go from these separate blue and yellow bits of chyme to a well-mixed green chyme down here at the bottom. Okay. You need to keep these separate in your head. You can remember the alliteration. Peristalsis is a push. It moves that chyme through the alimentary canal. Segmentation is a swish. It kind of swishes it back and forth and mixes it up.
We got practice after this, and give it a try.