12 Facts About Your Digestive System

The human digestive system is a lot “smarter” than you might think. In many ways the digestive system functions as a mini brain, commanding a handful of organs to break down that breakfast burrito you just inhaled, convert it into the nutrients that sustain you, and send it along the gastrointestinal tract until it comes out, uh, the other end. However, because it’s such a large and complex system, it’s also prone to a number of digestive diseases and disorders. Here are 11 things you might not know about your digestive system.

1. The digestive system includes 10 organs.

Before you even take your first bite of food, your salivary glands start producing enzyme-rich saliva in anticipation of the starches your body will need to break down. These glands are the first organ involved in the digestive system—a complicated network of 10 organs that span the entire length of your torso. Other organs involved include the pharynx (throat), esophagus, stomach, liver, gallbladder, pancreas, small intestine, large intestine, and rectum.

2. Your digestive system has its own nervous system.

The digestive process is controlled by the enteric nervous system, which functions independently of the brain but contains some of the same types of neurons and neurotransmitters. “In fact, there are so many of these neurons in the gastrointestinal tract that we think there are about as many neurons there as there are in our spinal cord,” says Geoffrey A. Preidis, a scientific advisory board member of the American Gastroenterological Association Center for Gut Microbiome Research & Education. Often called the body’s “second brain,” the enteric nervous system is capable of sensing the food you eat, producing hormones like serotonin, and controlling your gut muscles, to name just a couple of its functions. Some of these sensory neurons can even tell the brain when it’s time to lay off the cheese fries. “If we are bloated, those neurons can tell us, ‘Hey, this is a distended stomach or distended intestine,’ and it can signal pain or discomfort back up to the brain,” Preidis tells Mental Floss.

3. The digestive system feels when you're nervous or stressed.

This “second brain” also might explain why stress and anxiety can wreak havoc on one’s digestive system, at times causing “butterflies” in your belly or more malicious symptoms. “I think everybody can envision a circumstance in their own personal life in which there has been a really stressful situation and they’ve experienced some sort of gastrointestinal symptom, whether that is pain or a change in their bowel habits,” Preidis says. “Some people will be more sensitive to pain and some people will need to run to the restroom more frequently, so it’s very individualized.” When a fight-or-flight response is triggered in the brain, it can also cause digestion to slow or even come to a halt, allowing your body to instead focus on whatever threat you’re facing.

It’s unclear what exactly causes these gastrointestinal reactions to stress, though. A recent study in mice revealed that a specialized diet could alter their gut microbiome, thereby changing their brain chemicals and influencing their response to stress. “Of course rodents are not people, and no one is rushing out to make recommendations for patients with stress or anxiety,” says Preidis, who was not involved in that study, “but this could potentially drive clinical trials of that nature in the future.”

4. The next time beans make you gassy, blame your digestive system.

The reason why beans (the “musical fruit”) make you toot so much is because they contain complex carbohydrates that aren’t readily absorbed by the intestine on its own. But this digestive organ gets some assistance from all the bacteria that live in your intestinal tract and feast on your leftovers. Those bacteria help break down food, but they also create gassy by-products like hydrogen, carbon dioxide, and methane. It’s usually nothing to be concerned about, though. In some cases, gas can even be a sign of healthy gut microbes.

5. The digestive system's contact with the outside environment makes it unique.

Preidis says that part of what makes the digestive system unique, in terms of diseases and disorders, is that it comes into contact with the things from the outside world. “We ingest things, we swallow things from the environment, and they come into direct contact with the lining of our intestine,” Preidis says. “For that reason, many of the diseases have environmental causes—like inflammation from chronic alcohol ingestion—so the gut is right there on the front line of our defense against the environment.”

6. Physicians aren't sure what causes IBS, the most common digestive disorder ...

IBS is the digestive disorder most often diagnosed by gastroenterologists, according to the American College of Gastroenterology. Doctors still don't know exactly what causes it. The muscles lining the intestine appear to have something to do with it, though. These muscles contract as food makes its way through the gut, but longer and stronger contractions can lead to diarrhea, gas, and bloating. Problems affecting the nerves in the digestive system may also be at play, as well as changes in gut bacteria.

7. ... or why coffee makes some people poop.

Coffee has a laxative effect on about one-third of the population, but caffeine isn’t to blame. Scientists aren’t entirely sure what’s at work, but they do know that coffee stimulates the large intestine within four minutes of drinking it. They suspect it has to do with a compound in coffee that leads to a spike in the production of stomach acid. This, in turn, helps transport food at a faster rate through the digestive tract—and ultimately into your toilet.

8. You don’t really have to wait 30 minutes to swim after eating.

This belief held that after a big meal, blood was diverted to the body's core and away from the limbs, which weakened your arms and legs and increased the risk of drowning. The old wives' tale has long been scaring children (and adults) into sitting beside the pool while waiting for their lunch to digest. Well, we have some good news for you: It isn’t based in fact. While eating does divert some blood flow from the muscles to the digestive tract, it isn’t enough of a change to render your arms and legs immobile in the water. At most, you might get a minor cramp.

9. Ancient Greeks and Romans often ate lying down. That isn’t recommended for people today ...

Dining while reclining was seen as a power play in ancient Greece and Rome. It was a sign that someone—typically a man—had the luxury of lounging around and eating to his heart’s content while someone else served him. (The social customs in Greece dictated that women should eat sitting up, but some upper-class women in ancient Rome feasted in a supine position as well.) As James Brown, a biology lecturer at Aston University in Birmingham, UK, writes for The Conversation, lying on one’s left side can reduce pressure on the lower stomach, allowing one to pig out more comfortably. It may also allow carbohydrates to be absorbed more slowly, and therefore prevent spikes in insulin levels, but that’s pretty much where the benefits end. It could also lead to an increased risk of gastroesophageal reflux disease (GERD), and the American College of Gastroenterology recommends that people avoid lying down for two hours after eating.

10. ... but eating lying down is OK for cows.

Ruminants may look lazy, but studies have shown that chewing cud—partially digested food that has been regurgitated from a cow's four stomach chambers—is an important part of its digestive process. Through the process of evolution, cattle are able to eat larger quantities of grass without having to worry about chewing it up. Once they’ve had their fill, the cattle lie down and regurgitate their food, allowing microorganisms to break it down so that they can digest their food more thoroughly.

11. Digestive system functions don't have anything to do with gravity.

Though experts warn against eating while lying down, this suggestion isn't related to gravitational force. That’s because digestion is aided not by physics, but by peristalsis—the contracting of muscles along the digestive tract to transport food through the body. It explains why astronauts are still able to digest their freeze-dried space spaghetti in zero-gravity conditions.

12. Digestive systems vary greatly from one species to the next.

While animals like cows, deer, and giraffes have four-chambered stomachs, other animals, including seahorses, chimeras, and platypuses, have no stomach at all. In the case of platypuses, food travels from the esophagus directly to the intestines. As for seahorses, they are almost constantly wolfing down brine shrimp—often 3000 or more per day—because the digestive process happens so quickly. On the flip side of that, sloths have one of the slowest digestive systems. It can take a month for their stomachs to digest a single meal, which explains why they try to conserve energy by moving as little as possible. It's not laziness—it's a survival tactic.