Your gut has a mind of its own. A “second brain” of nervous system cells, including glia (stained green in this cross section of a mouse esophagus), coordinates the movement and digestion of food as it moves through your body.
From the moment you swallow a bite of food to the moment it exits your body, the gut is toiling to process this strange outside material. It has to break chunks down into small bits. It must distinguish healthy nutrients from toxins or pathogens and absorb only what is beneficial. And it does all this while moving the partially processed food one way through different factories of digestion — mouth, esophagus, stomach, through the intestines and out.
“Digestion is required for survival,” said Marissa Scavuzzo, a postdoctoral researcher at Case Western Reserve University in Ohio. “We do it every day, but also, if you really think about it, it sounds very foreign and alien.”
Breaking down food requires coordination across dozens of cell types and many tissues — from muscle cells and immune cells to blood and lymphatic vessels. Heading this effort is the gut’s very own network of nerve cells, known as the enteric nervous system, which weaves through the intestinal walls from the esophagus down to the rectum. This network can function nearly independently from the brain; indeed, its complexity has earned it the nickname “the second brain.” And just like the brain, it’s made up of two kinds of nervous system cells: neurons and glia.