We all know what the brain is and how important it is to our existence. But what many of us may not know is that our body has a ‘second brain’ that lives inside our gut i.e., the gastrointestinal tract consisting of the esophagus, stomach and the intestines.

A key function of the gut is to break down food, something we hardly think about until something goes wrong. This process requires complex 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, that 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.”

Just like the brain, the enteric nervous system is made up of two kinds of nervous system cells: neurons and glia. There are some 500 million neurons that controls important reflexes, such as peristalsis, the involuntary contraction and relaxation of different groups of muscles throughout the digestive tract. And there are the neglected glial cells (pictured below).

For the longest time, glia cells were thought to play a passive role in the enteric nervous system, serving as some sort of glue that fills the space between neurons. But recent advances in neuroscience have led to new discoveries indicating that glia, far from being passive, play important physiological roles in the brain and nervous system that once seemed reserved for neurons.

A variety of glial cells exist in the gut system, some of which sense food as it moves through the digestive tract, signaling to the gut tissue to contract and move it along its way. Enteric glia also help maintain the gut’s barrier to keep toxins out, and when trouble comes, they are also among the first responders to injury or inflammation in gut tissue. Because of this, scientists now believe glial play a role in many gastrointestinal disorders and diseases, making them good potential targets for treatment. As if that is not enough, enteric glial busily communicate with our microbiome (the gut’s reservoir of good bacteria), neurons and immune-system cells, managing and coordinating their functions. “We think that they do everything,” sums up Brian Gulbransen, a neuroscientist at Michigan State University. “The more that people find out about them, it’s less surprising that they do these diverse roles.”

Note: This post is adapted from a Quanta Magazine article posted online titled, ‘In the gut’s second brain, key agents of health emerge’ by Yasemin Saplakoglu dated Nov 21, 2023.