What does it mean when your stomach rumbles? How do our bodies extract nutrients and vitamins from food? Does what you eat affect your mood? Digestion is an invisible, effortless, unconscious process—and one that, until recently, we knew almost nothing about. On this episode of Gastropod, we follow our food on its journey to becoming fuel, from the filtered blood that helps slide food into the stomach, to the velvet walls and rippling choreography of the small intestine, to the microbial magic of the colon and out the other end. And we do it by visiting the world's most sophisticated artificial gut at dinner time—a plumbing marvel named TIM that chews, swallows, squeezes, farts, and poops just like the real thing.
Before the invention of refrigeration, cadavers that early scientists dissected to learn about human physiology usually had their guts removed, to help reduce the stink. As a result, the digestive system largely remained a black box—food went in, the processed remains came out—until a window opened that black box in 1822, in the form of a bullet hole in the stomach of Alexis St. Martin. An impoverished French Canadian trapper, he worked for the American Fur Company until he was accidentally shot. As Mary Roach, author of Gulp: Adventures on the Alimentary Canal, told Gastropod, a surgeon named William Beaumont discovered that the bullet hole offered a literal opening into the mysterious workings of the stomach, because St. Martin's "breakfast kind of spilled out." Roach says it's unclear whether Beaumont did his best to heal St. Martin: "He says that he did. But, I'm just guessing, maybe he kind of saw an opportunity here."
For more than a decade, the two enjoyed a strange relationship, each dependent on the other. St. Martin lived at Beaumont's house, and Beaumont took advantage of the unhealed stomach opening to dangle food in on a string, to learn that stomach acid can digest food even without the stomach's vise-like squeeze. Today, Beaumont is recognized as one of the fathers of modern physiology.
TIM 1, with stomach and small intestine (left); TIM's inputs are stored on shelves at the side of the cabinet (right, top); TIM's chewing machine (right, bottom). Photos by Nicola Twilley.
Though scientists have long moved past the food-on-a-string method of research, the current techniques for investigating how we process our food, as digestion is occurring in our bodies, remain invasive and expensive. And so researchers also rely on sophisticated models of the gut that attempt to mimic every critical stop along the thirty-odd feet our of digestive systems. To learn what these models can teach us, we traveled to the Netherlands to visit TIM, the world's most sophisticated model gut, at the Dutch public-private research organization TNO. TIM's entire system fills two huge beige cabinets of silicone tubes and metal valves, from its mouth input funnel to the fart tube that removes the smelly gas produced at the other end.
TIM's system is larger than life—but biologist Don Ingber and his colleaugues at the Wyss Institute for Biologically Inspired Engineering at Harvard University have shrunk the large and small intestines down to two small, flexible squares of clear rubber. On each "organ-on-a-chip," nearly invisible tubes are lined with cells from our intestinal walls—cells whose function mimics the activity in our own real intestinal walls.
To compare these models to the real thing, we spoke with Giulia Enders, doctor and author of Gut, The Inside Story of our Bodies’ Most Underrated Organ, and perhaps the biggest gut fan of all. Enders explains how the gut acts as a second brain in the body, with its own form of consciousness. By the time we’re through, you’ll have a new appreciation for the gut as a thing of beauty—and you may never be embarrassed by a rumbling stomach again. Listen in now!
Giulia Enders is a medical doctor and author currently studying for her Ph.D. in gastroenterology at the Institute for Microbiology and Hospital Hygiene in Frankfurt. She's the author of Gut: The Inside Story of Our Body's Most Underrated Organ.
Susann Bellman, Mans Minekus, and TIM, TNO
TIM 2, the large intestine. Photo by Nicola Twilley.
Don Ingber is the founding director of the Wyss Institute for Biologically Inspired Engineering at Harvard and lead inventor of the organs-on-a-chip.