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 causingbutterflies” 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.

‘Water’ in Kansas City Woman’s Ear Turned Out to Be a Venomous Brown Recluse Spider

N-sky/iStock via Getty Images
N-sky/iStock via Getty Images

Susie Torres, a resident of Kansas City, Missouri, woke up on Tuesday morning with the distinct feeling that water was lodged in her left ear. She likened it to the swooshing sensation that can often happen after swimming, WDAF-TV reports.

Instead of waiting for the problem to resolve itself, Torres went to the doctor—a decision that might have saved her from some serious pain. The medical assistant was the first to realize something was alarmingly amiss, and immediately called for backup.

“She ran out and said ‘I’m going to get a couple more people,’” Torres told 41 Action News. “She then said, ‘I think you have an insect in there.’” For many people, the thought of having any live insect stuck in an ear would be enough to cue a small- or large-scale freak-out, but Torres stayed calm.

The doctors “had a few tools and worked their magic and got it out,” Torres said. The “it” in question turned out to be a spider—and not just any harmless house spider (which you shouldn’t kill, by the way). It was a venomous brown recluse spider.

“Gross,” Torres told WDAF-TV. “Why, where, what, and how.”

Miraculously, the spider didn’t bite Torres. If it had, she would’ve ended up visiting the doctor with more than general ear discomfort: Brown recluse bites can cause pain, burning, fever, nausea, and purple or blue discoloration of the surrounding skin, according to Healthline.

Torres may have remained admirably level-headed throughout the ordeal, but that doesn’t mean she’s taking it lightly. “I went and put some cotton balls in my ears last night,” she told WDAF-TV. “I’m shaking off my clothes, and I don’t put my purse on the floor. I’m a little more cautious.”

Is this the first time an insect has posted up in the ear of an unsuspecting, innocent human? Absolutely not—here are six more horror stories, featuring a cockroach, a bed bug, and more.

[h/t WDAF-TV]

12 Fantastic Facts About the Immune System

monkeybusinessimages/iStock via Getty Images
monkeybusinessimages/iStock via Getty Images

If it weren't for our immune system, none of us would live very long. Not only does the immune system protect us from external pathogens like viruses, bacteria, and parasites, but it also battles cells that have mutated due to illnesses, like cancer, within the body. Here are 12 fascinating facts about the immune system.

1. The immune system saves lives.

The immune system is a complex network of tissues and organs that spreads throughout the entire body. In a nutshell, it works like this: A series of "sensors" within the system detects an intruding pathogen, like bacteria or a virus. Then the sensors signal other parts of the system to kill the pathogen and eliminate the infection.

"The immune system is being bombarded by all sorts of microbes all the time," Russell Vance, professor of immunology at University of California, Berkeley and an investigator for the Howard Hughes Medical Institute, tells Mental Floss. "Yet, even though we're not aware of it, it's saving our lives every day, and doing a remarkably good job of it."

2. Before scientists understood the immune system, illness was chalked up to unbalanced humors.

Long before physicians realized how invisible pathogens interacted with the body's system for fighting them off, doctors diagnosed all ills of the body and the mind according to the balance of "four humors": melancholic, phlegmatic, choleric, or sanguine. These criteria, devised by the Greek philosopher Hippocrates, were divided between the four elements, which were linked to bodily fluids (a.k.a. humors): earth (black bile), air (blood), water (phlegm) and fire (yellow bile), which also carried properties of cold, hot, moist, or dry. Through a combination of guesswork and observation, physicians would diagnose patients' humors and prescribe treatment that most likely did little to support the immune system's ability to resist infection.

3. Two men who unraveled the immune system's functions were bitter rivals.

Two scientists who discovered key functions of the immune system, Louis Pasteur and Robert Koch, should have been able to see their work as complementary, but they wound up rivals. Pasteur, a French microbiologist, was famous for his experiments demonstrating the mechanism of vaccines using weakened versions of the microbes. Koch, a German physician, established four essential conditions under which pathogenic bacteria can infect hosts, and used them to identify the Mycobacterium tuberculosis bacterium that causes tuberculosis. Though both helped establish the germ theory of disease—one of the foundations of modern medicine today—Pasteur and Koch's feud may have been aggravated by nationalism, a language barrier, criticisms of each other's work, and possibly a hint of jealousy.

4. Specialized blood cells are the immune system's greatest weapon.

The most powerful weapons in your immune system's arsenal are white blood cells, divided into two main types: lymphocytes, which create antigens for specific pathogens and kill them or escort them out of the body; and phagocytes, which ingest harmful bacteria. White blood cells not only attack foreign pathogens, but recognize these interlopers the next time they meet them and respond more quickly. Many of these immune cells are produced in your bone marrow but also in the spleen, lymph nodes, and thymus, and are stored in some of these tissues and other areas of the body. In the lymph nodes, which are located throughout your body but most noticeably in your armpits, throat, and groin, lymphatic fluid containing white blood cells flows through vein-like tubules to escort foreign invaders out.

5. The spleen helps your immune system work.

Though you can live without the spleen, an organ that lies between stomach and diaphragm, it's better to hang onto it for your immune function. According to Adriana Medina, a doctor who specializes in hematology and oncology at the Alvin and Lois Lapidus Cancer Institute at Sinai Hospital in Baltimore, your spleen is "one big lymph node" that makes new white blood cells and cleans out old blood cells from the body.

It's also a place where immune cells congregate. "Because the immune cells are spread out through the body," Vance says, "eventually they need to communicate with each other." They do so in both the spleen and lymph nodes.

6. You have immune cells in all of your tissues.

While immune cells may congregate more in lymph nodes than elsewhere, "every tissue in your body has immune cells stationed in it or circulating through it, constantly roving for signs of attack," Vance explains. These cells also circulate through the blood. The reason for their widespread presence is that there are thousands of different pathogens that might infect us, from bacteria to viruses to parasites. "To eliminate each of those different kinds of threats requires specialized detectors," he says.

7. How friendly you're feeling could be linked to your immune system.

From an evolutionary perspective, humans' high sociability may have less to do with our bigger brains, and more to do with our immune system's exposure to a greater number of bacteria and other pathogens.

Researchers at the University of Virginia School of Medicine have theorized that interferon gamma (IG), a substance that helps the immune system fight invaders, was linked to social behavior, which is one of the ways we become exposed to pathogens.

In mice, they found IG acted as a kind of brake to the brain's prefrontal cortex, essentially stopping aberrant hyperactivity that can cause negative changes in social behavior. When they blocked the IG molecule, the mice's prefrontal cortexes became hyperactive, resulting in less sociability. When they restored the function, the mice's brains returned to normal, as did their social behavior.

8. Your immune system might recruit unlikely organs, like the appendix, into service.

The appendix gets a bad rap as a vestigial organ that does nothing but occasionally go septic and create a need for immediate surgery. But the appendix may help keep your gut in good shape. According to Gabrielle Belz, professor of molecular immunology at the Walter and Eliza Hall Institute of Medical Research in Melbourne, Australia, research by Duke University's Randal Bollinger and Bill Parker suggests the appendix houses symbiotic bacteria that are important for overall gut health—especially after infections wipe out the gut's good microbes. Special immune cells known as innate lymphoid cells (ILCs) in the appendix may help to repopulate the gut with healthy bacteria and put the gut back on track to recovery.

9. Gut bacteria has been shown to boost immune systems in mice.

Researchers at the University of Chicago noticed that one group of mice in their lab had a stronger response to a cancer treatment than other mice. They eventually traced the reason to a strain of bacteria—Bifidobacterium—in the mice's guts that boosted the animals' immune system to such a degree they could compare it to anti-cancer drugs called checkpoint inhibitors, which keep the immune system from overreacting.

To test their theory, they transferred fecal matter from the robust mice to the stomachs of less immune-strengthened mice, with positive results: The treated mice mounted stronger immune responses and tumor growth slowed. When they compared the bacterial transfer effects with the effects of a checkpoint inhibitor drug, they found that the bacteria treatment was just as effective. The researchers believe that, with further study, the same effect could be seen in human cancer patients.

10. Scientists are trying to harness the immune system's "Pac-Man" cells to treat cancer.

Aggressive pediatric tumors are difficult to treat due to the toxicity of chemotherapy, but some researchers are hoping to develop effective treatments without the harmful side effects. Stanford researchers designed a study around a recently discovered molecule known as CD47, a protein expressed on the surface of all cells, and how it interacts with macrophages, white blood cells that kill abnormal cells. "Think of the macrophages as the Pac-Man of the immune system," Samuel Cheshier, lead study author and assistant professor of neurosurgery at Stanford Medicine, tells Mental Floss.

CD47 sends the immune system's macrophages a "don't eat me" signal. Cancer cells fool the immune system into not destroying them by secreting high amounts of CD47. When Cheshier and his team blocked the CD47 signals on cancer cells, the macrophages could identify the cancer cells and eat them, without toxic side effects to healthy cells. The treatment successfully shrank all five of the common pediatric tumors, without the nasty side effects of chemotherapy.

11. A new therapy for type 1 diabetes tricks the immune system.

In those with type 1 diabetes, the body attacks its own pancreatic cells, interrupting its normal ability to produce insulin in response to glucose. In a 2016 paper, researchers at MIT, in collaboration with Boston's Children's Hospital, successfully designed a new material that allows them to encapsulate and transplant healthy pancreatic "islet" cells into diabetic mice without triggering an immune response. Made from seaweed, the substance is benign enough that the body doesn't react to it, and porous enough to allow the islet cells to be placed in the abdomen of mice, where they restore the pancreatic function. Senior author Daniel Anderson, an associate professor at MIT, said in a statement that this approach "has the potential to provide [human] diabetics with a new pancreas that is protected from the immune system, which would allow them to control their blood sugar without taking drugs. That's the dream."

12. Immunotherapy is on the cutting edge of immune system research.

Over the last few years, research in the field of immunology has focused on developing cancer treatments using immunotherapy. This method engineers the patient's own normal cells to attack the cancer cells. Vance says the technique could be used for many more conditions. "I feel like that could be just the tip of the iceberg," he says. "If we can understand better what the cancer and immunotherapy is showing, maybe we can go in there and manipulate the immune responses and get good outcomes for other diseases, too."