12 Facts About Your Digestive System

iStock.com/yodiyim
iStock.com/yodiyim

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.

7 Facts About Blood

Moussa81/iStock via Getty Images
Moussa81/iStock via Getty Images

Everyone knows that when you get cut, you bleed—a result of the constant movement of blood through our bodies. But do you know all of the functions the circulatory system actually performs? Here are some surprising facts about human blood—and a few cringe-worthy theories that preceded the modern scientific understanding of this vital fluid.

1. Doctors still use bloodletting and leeches to treat diseases.

Ancient peoples knew the circulatory system was important to overall health. That may be one reason for bloodletting, the practice of cutting people to “cure” everything from cancer to infections to mental illness. For the better part of two millennia, it persisted as one of the most common medical procedures.

Hippocrates believed that illness was caused by an imbalance of four “humors”—blood, phlegm, black bile, and yellow bile. For centuries, doctors believed balance could be restored by removing excess blood, often by bloodletting or leeches. It didn’t always go so well. George Washington, for example, died soon after his physician treated a sore throat with bloodletting and a series of other agonizing procedures.

By the mid-19th century, bloodletting was on its way out, but it hasn’t completely disappeared. Bloodletting is an effective treatment for some rare conditions like hemochromatosis, a hereditary condition causing your body to absorb too much iron.

Leeches have also made a comeback in medicine. We now know that leech saliva contains substances with anti-inflammatory, antibiotic, and anesthetic properties. It also contains hirudin, an enzyme that prevents clotting. It lets more oxygenated blood into the wound, reducing swelling and helping to rebuild tiny blood vessels so that it can heal faster. That’s why leeches are still sometimes used in treating certain circulatory diseases, arthritis, and skin grafting, and helps reattach fingers and toes. (Contrary to popular belief, even the blood-sucking variety of leech is not all that interested in human blood.)

2. Scientists didn't understand how blood circulation worked until the 17th century.

William Harvey, an English physician, is generally credited with discovering and demonstrating the mechanics of circulation, though his work developed out of the cumulative body of research on the subject over centuries.

The prevailing theory in Harvey’s time was that the lungs, not the heart, moved blood through the body. In part by dissecting living animals and studying their still-beating hearts, Harvey was able to describe how the heart pumped blood through the body and how blood returned to the heart. He also showed how valves in veins helped control the flow of blood through the body. Harvey was ridiculed by many of his contemporaries, but his theories were ultimately vindicated.

3. Blood types were discovered in the early 20th century.

Austrian physician Karl Landsteiner discovered different blood groups in 1901, after he noticed that blood mixed from people with different types would clot. His subsequent research classified types A, B and O. (Later research identified an additional type, AB). Blood types are differentiated by the kinds of antigens—molecules that provoke an immune system reaction—that attach to red blood cells.

People with Type A blood have only A antigens attached to their red cells but have B antigens in their plasma. In those with Type B blood, the location of the antigens is reversed. Type O blood has neither A nor B antigens on red cells, but both are present in the plasma. And finally, Type AB has both A and B antigens on red cells but neither in plasma. But wait, there’s more! When a third antigen, called the Rh factor, is present, the blood type is classified as positive. When Rh factor is absent, the blood type is negative.

Scientists still don’t understand why humans have different blood types, but knowing yours is important: Some people have life-threatening reactions if they receive a blood type during a transfusion that doesn’t “mix” with their own. Before researchers developed reliable ways to detect blood types, that tended to turn out badly for people receiving an incompatible human (or animal!) blood transfusion.

4. Blood makes up about 8 percent of our total body weight.

Adult bodies contain about 5 liters (5.3 quarts) of blood. An exception is pregnant women, whose bodies can produce about 50 percent more blood to nourish a fetus.)

Plasma, the liquid portion of blood, accounts for about 3 liters. It carries red and white blood cells and platelets, which deliver oxygen to our cells, fight disease, and repair damaged vessels. These cells are joined by electrolytes, antibodies, vitamins, proteins, and other nutrients required to maintain all the other cells in the body.

5. A healthy red blood cell lasts for roughly 120 days.

Red blood cells contain an important protein called hemoglobin that delivers oxygen to all the other cells in our bodies. It also carries carbon dioxide from those cells back to the lungs.

Red blood cells are produced in bone marrow, but not everyone produces healthy ones. People with sickle cell anemia, a hereditary condition, develop malformed red blood cells that get stuck in blood vessels. These blood cells last about 10 to 20 days, which leads to a chronic shortage of red blood cells, often causing to pain, infection, and organ damage.

6. Blood might play a role in treating Alzheimer's disease.

In 2014, research led by Stanford University scientists found that injecting the plasma of young mice into older mice improved memory and learning. Their findings follow years of experiments in which scientists surgically joined the circulatory systems of old and young mice to test whether young blood could reverse signs of aging. Those results showed rejuvenating effects of a particular blood protein on the organs of older mice.

The Stanford team’s findings that young blood had positive effects on mouse memory and learning sparked intense interest in whether it could eventually lead to new treatments for Alzheimer’s disease and other age-related conditions.

7. The sight of blood can make people faint.

For 3 to 4 percent of people, squeamishness associated with blood, injury, or invasive medical procedures like injections rises to the level of a true phobia called blood injury injection phobia (BII). And most sufferers share a common reaction: fainting.

Most phobias cause an increase in heart rate and blood pressure, and often muscle tension, shakes, and sweating: part of the body’s sympathetic nervous system’s “fight or flight” response. But sufferers of BII experience an added symptom. After initially increasing, their blood pressure and heart rate will abruptly drop.

This reaction is caused by the vagus nerve, which works to keep a steady heart rate, among other things. But the vagus nerve sometimes overdoes it, pushing blood pressure and heart rate too low. (You may have experienced this phenomenon if you’ve ever felt faint while hungry, dehydrated, startled, or standing up too fast.) For people with BII, the vasovagal response can happen at the mere sight or suggestion of blood, needles, or bodily injury, making even a routine medical or dental checkup cause for dread and embarrassment.

What Purpose Does the Belly Button Serve?

misuma/iStock via Getty Images
misuma/iStock via Getty Images

While your eyelashes are protecting your eyes, your lungs are letting you breathe, and virtually every other part of your body—inside and out—is performing its own relatively well-known task, your belly button is just sitting there collecting lint. And while it’s true that your navel served its most important purpose before you were born, it’s not totally useless now.

According to ZME Science, back when you were a fetus, your belly button was more of a belly portal: Your umbilical cord extended from it and connected you to the placenta on your mother’s uterine wall. That way, the placenta could channel nutrients and oxygen to you through the cord, and you could send back waste.

Your umbilical cord was cut when you were born, creating a tiny bulge that left behind some scar tissue after it healed. That scar tissue is your belly button, navel, or umbilicus. Though you may have heard that the shape of your belly button is a direct result of the scissor skills of the doctor who delivered you, that’s not true. Dr. Dan Polk, a neonatologist in the Chicago area, told the Chicago Tribune that a belly button's shape “has to do with how much baby skin leads onto the umbilical cord from the baby’s body. Less skin makes an innie; more skin makes an outie.” About 90 percent of people have innies.

Regardless of how your belly button looks, you probably don’t use it on a daily basis. However, if you’ve studied anatomy, medicine, or a related field, you might recognize it as the central point by which the abdomen is divided into the following quadrants: right upper, left upper, right lower, and left lower. Another way of classifying that area is into nine regions—including the hypochondriac, lumbar, iliac, epigastric, and hypogastric regions—with the umbilical region at the very center.

Abdominopelvic regions diagram
Blausen Medical, Wikimedia Commons // CC BY 3.0

Your belly button can also serve as the opening for laparoscopic surgery, which can save you from having a scar elsewhere on your abdomen.

The navel is a great central landmark outside of medicine, too. If you’ve taken yoga or Pilates classes, you may have heard it referred to as the center of balance or center of gravity. Because it sits right on top of your abdominal muscles, your belly button is an easy marker for your instructor to mention when they want you to access your core, which helps you balance.

And, of course, belly buttons are notorious for storing quite a bit of lint, which always seems to be blue (you can learn more about that here).

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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