The human body is an amazing thing. For each one of us, it's the most intimate object we know. And yet most of us don't know enough about it: its features, functions, quirks, and mysteries. Our series The Body explores human anatomy, part by part. Think of it as a mini digital encyclopedia with a dose of wow.
When we talk about the belly, gut, or bowels, what we're really talking about are the intestines—long, hollow, coiled tubes that comprise a major part of the digestive tract, running from the stomach to the anus. The intestines begin with the small intestine, divided into three parts whimsically named the duodenum, jejunum, and ileum, which absorb most of the nutrients from what we eat and drink. Food then moves into the large intestine, or colon, which absorbs water from the digested food and expels it into the rectum. That's when sensitive nerves in your rectum create the sensation of needing to poop.
Colby Zaph, a professor of immunology in the department of Biochemistry and Molecular Biology at Melbourne's Monash University, shares with Mental Floss important facts about how your body processes your food.
1. YOUR INTESTINES WERE NAMED BY MEDIEVAL ANATOMISTS.
Medieval anatomists had a pretty good understanding of the physiology of the gut, and are the ones who gave the intestinal sections their names, which are still used today in modern anatomy. When they weren't moralizing about the organs, they got metaphorical about them. In 1535, the Spanish doctor Andrés Laguna noted that because the intestines "carry the chyle and all the excrement through the entire region of the stomach as if through the Ocean Sea," they could be likened to "those tall ships which as soon as they have crossed the ocean come to Rouen with their cargoes on their way to Paris but transfer their cargoes at Rouen into small boats for the last stage of the journey up the Seine."
2. LEONARDO DA VINCI BELIEVED THE INTESTINES HELPED YOU BREATHE.
Da Vinci mistakenly believed the digestive system aided the respiratory function. In 1490, he wrote in his unpublished notebooks, "The compressed intestines with the condensed air which is generated in them, thrust the diaphragm upwards; the diaphragm compresses the lungs and expresses the air." While that isn't anatomically accurate, it is true that the opening of the lungs is helped by the relaxation of stomach muscles, which does draw down the diaphragm.
3. YOUR INTESTINES COULD COVER TWO TENNIS COURTS …
Your intestines take up a whole lot of square footage inside you. "The surface area of the intestines if laid out flat would cover two tennis courts," Zaph says. The small intestine alone is about 20 feet long, and the large intestine about 5 feet long.
4. … AND THEY'RE PRETTY ATHLETIC.
5. YOUR BOWELS CAN FOLD LIKE A TELESCOPE. (THIS IS NOT GOOD.)
That's not something you want to happen. Intussusception is the name of a condition where a part of your intestine folds in on itself, usually between the lower part of the small intestine and the beginning of the large intestine. It often presents as severe pain in the abdomen and requires immediate medical attention. It's very rare, and in children may be related to a viral infection. In adults, it's more commonly a symptom of an abnormal growth or polyp.
6. INTESTINES ARE VERY DISCRIMINATING.
"The intestines have to discriminate between good things—food, water, vitamins, good bacteria—and bad things—infectious organisms like viruses, parasites and bad bacteria," Zaph says. Researchers don't entirely know how the intestines do this, but they do know that "good bacteria don't live in the mucus layer close to the intestinal epithelial cells." Zaph explains that while your intestines are designed to keep dangerous bacteria contained, infectious microbes can sometimes penetrate your immune system through your intestines.
7. YOUR SMALL INTESTINE HAS MANY "FINGERS" …
The lining of the small intestine is covered in tiny finger-like protrusions known as villi. These villi are then covered in even tinier protrusions called microvilli, which help capture food particles to absorb nutrients, and help move food on to the large intestine.
8. … AND YOU CAN’T LIVE WITHOUT IT.
Your small intestine "is the sole point of food and water absorption," Zaph says. Without it, "you'd have to be fed through the blood."
9. YOUR GUT IS HOME TO A MARVELOUS MICROSCOPIC WORLD KNOWN AS THE MICROBIOME.
The microbiome is made up of all kinds of microorganisms, including bacteria, viruses, fungi, and protozoans, "and probably used to include worm parasites too," says Zaph. So in a way, he adds, "we are constantly infected with something, but it [can be] helpful, not harmful."
10. YOUR GUT IS VERY SENSITIVE TO CHANGES.
Zaph says that many things change the composition of the microbiome: antibiotics, foods we eat, stress, infections. But in general, most people return to a stable microbiome after these events. "The microbiome composition is different between many people, and affected by diseases. But we still don't know whether the different microbiomes cause disease, or are a result in the development of disease."
11. TRANSFERRING BACTERIA FROM ONE GUT TO ANOTHER CAN TRANSFER DISEASE—OR POSSIBLY CURE IT.
"Studies in mice show that transplanting microbes from obese mice can transfer obesity to thin mice," Zaph says. But transplanting microbes from healthy people into sick people can be a powerful treatment for some gut infections, like that of the bacteria Clostridium difficile, he adds. Research is pouring out on how the microbiome affects various diseases, including multiple sclerosis, Parkinson's, and even autism.
12. YOUR GUT MICROBIOME MAY INFLUENCE HOW YOU RESPOND TO MEDICAL TREATMENT.
Some people don't respond to cancer drugs as effectively as others, Zaph says. "One reason is that different microbiomes can metabolize the drugs differently." This has huge ramifications for chemotherapy and new cancer treatments called checkpoint inhibitors. As scientists learn more about how different bacteria metabolize drugs, they could possibly improve how effective existing cancer treatments are.