13 Fundamental Facts About the Anus

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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.

The anus might be the most underappreciated part of the body. Its very mention generally causes people to giggle or cringe. Yet without it, you'd be unable to eliminate waste and eventually die. In case your childhood wasn't enough to give you an accurate idea of its location, the anus is essentially the valve that stands between your poop and the toilet. It's considered the last piece of your digestive tract, essentially a two-inch long canal comprised of pelvic floor muscles and sphincters, easy to locate below either your vagina or your scrotum.

1. IT HAS TWO SPHINCTERS …

You may have heard talk of your "anal sphincter," which is not just one, but two valves. The internal sphincter is involuntary, meaning you can't squeeze it open—it's always closed up tight until it's time to poop. You can consciously hold closed the external, voluntary sphincter if you have to go to the bathroom but there's no toilet in sight, and consciously choose to open it when you're ready to poop. Thanks to your pelvic floor muscle, your poop normally doesn't come out when you don't want it to.

2. …AND ONE VERY IMPORTANT ROLE.

"The most important role is to eliminate waste," Rafael Lugo, a colorectal surgeon in Houston, tells Mental Floss. "We don't think much of it, but it's very important because if we don't eliminate waste, we have a [serious] problem." In rare cases, long-term constipation can cause illness and even death.

3. YOU REALLY SHOULD TAKE A LOOK AT IT … FOR YOUR HEALTH.

Since some of the health conditions of the anus don't cause any immediate symptoms you can feel, Lugo recommends you get comfortable looking at your anus from time to time. "We have these taboos in this society about looking at our bodies. Your body is your body. Touch it. The best place is in the shower. You have soap, feel the area. If anything is abnormal, take it to a mirror," he says. Once a year, have a professional look at it. He says he finds a lot of abnormalities that people live with and don't even know can be treated, such as fissures, hemorrhoids, and even cancer.

4. A SELF-CHECK CAN CATCH ANAL CANCER IN ITS EARLY STAGES.

"We can't control how [anal] melanoma happens, but it can be addressed early if you keep an eye on your butt. You can detect these changes early on and not die from it," Lugo advises. He recommends you "know your body head to toe. People tend to notice the dent in their car more often than they notice an issue in their body."

5. YOU DON'T HAVE TO SUNTAN TO GET ANAL CANCER.

Anal carcinoma, unfortunately, is not something you can usually feel with your hand. "It doesn't grow a tumor like a melanoma," Lugo says. "There's no bump." This kind of cancer can be genetic and is further reason to see a proctologist once a year, particularly if you have a family history of cancer.

6. ANAL SEX SLIGHTLY INCREASES YOUR RISK OF CANCER FROM THE HPV VIRUS.

Another form of anal carcinoma is caused by the human papilloma virus (HPV) that causes genital warts. While this virus can spread from a penis or vagina to an anus, chances of transmission are greater by anal sex. Unlike the convenient test for the HPV virus in the vagina, there's not a similar test for signs of HPV of the anus. This is another reason why having a professional look at your anus is a good idea. "There might be a little wart, something that looks abnormal. If you're sexually active, have multiple partners, or having high-risk sex, you should be more vigilant every few months," Lugo says.

7. THERE'S NOTHING DIRTY ABOUT THE ANUS.

So long as you handle your basic hygiene, your anus isn't dirty, Lugo insists. He says the anus doesn't require soap to stay clean, just water and wiping. In fact, soaps and shampoos can irritate and dry out the sensitive skin of the anus, so go easy on those. "It's a very complex organ that we basically disregard," says Lugo.

8. HUMANS HAVE WIPED THEIR BUTTS IN A LOT OF WAYS.

Over the centuries, before the advent of toilet paper, humans turned to a wide variety of objects with which to wipe their butts, including "leaves, grass, stones, corn cobs, animal furs, sticks, snow, seashells, and, lastly, hands," as Scientific American reported. Notice that most of these objects are hard, and you might really appreciate that squeezably soft Charmin.

9. BUTT HAIR IS NORMAL.

In your infrequent inspection of your anus, you may discover that hair grows down there. Scientists aren't entirely sure why. That hasn't stopped us laypeople from asking, though. In fact, so many SciShow viewers asked host Hank Green to tackle the subject that he dedicated an episode to it. The prevailing theories can be summed up as: 1. we simply haven't evolved away from hair there, because it doesn't get in the way of elimination or procreation; 2. it helps conduct scents that our ancient selves relied upon for reproductive purposes; or 3. it helps prevent irritation or chafing in that sensitive tissue.

10. HEMORRHOIDS ARE VARICOSE VEINS OF THE ANUS.

The veins in your anus "help the anus seal," like a closing door, says Lugo. But when you get a hemorrhoid, essentially just a swollen, dilated vein, "it's like having a shoe in the door, because there's something uneven there." Not only can hemorrhoids bleed, throb and itch, they can lead to a condition called anal seepage. "There are many modalities to take care of them, but they're not very comfortable, and you may need a surgery to take care of it," Lugo says.

11. IT IS POSSIBLE TO PREVENT HEMORRHOIDS.

The key to preventing hemorrhoids is avoiding constipation and straining on the toilet. "Prevention is important: Keep your stool soft, [take] plenty of fiber, and drink plenty of water," Lugo advises.

12. TRY NOT TO SIT ON THE TOILET FOR MORE THAN FIVE MINUTES.

Don't spend more than five minutes on the toilet, Lugo advises. "You shouldn't be sitting there having a social event." When you sit on the toilet seat, gravity exerts its pull on tissues, including hemorrhoids. "When your butt is hanging there, all the blood [flows] into there. Hemorrhoids are like balloons, they stretch and contract."

13. BURNING SENSATION? IT MAY NOT BE WHAT YOU THINK.

A burning or hot sensation of the anus is not always a hemorrhoid. It could be an anal fissure, or a tiny tear in the lining of the anus. "This can happen after a large bowel movement, especially if you already suffer constipation, which can stretch the anus," Lugo says. These can be treated by sitting in a hot bath for 20 minutes a day until the tissue heals. In cases where the fissure recurs and won't go away, surgery may be necessary.

Here’s What Happens to Your Body During Anaphylaxis

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According to the Centers for Disease Control and Prevention, allergies affect more than 50 million Americans every year—and anaphylaxis, the most severe allergic reaction, affects at least 1.6 percent of the general population [PDF]. Here’s the science of what happens to the body during anaphylactic shock.

ALLERGEN EXPOSURE

In a person with allergies, cells sometimes identify foreign but innocuous stimuli as major threats. Why some people are allergic to certain things while others are not is a mystery science hasn't yet solved, but we do know how it happens: through a process called sensitization.

Here’s how it works. When the body encounters a foreign substance, also called an antigen, immune system cells deliver some of substance's molecules to T-helper cells living in the lymph nodes. Those cells also bring along a type of molecule that informs a T-helper cell it’s time to stage an immune response. Known as a costimulatory molecule, it's necessary to activate any type of immune system reaction involving T cells, whether you have allergies or not.

Being exposed to an antigen "primes" a T-helper cell, turning it into a Th2 cell. Primed Th2 cells release proteins called interleukins, which do two things: First, they interact with another type of immune cell called B cells to produce infection-fighting antibodies that bind to mast cells, which contain chemical particles they'll release in the presence of an antigen. Second, the interleukins activate eosinophils, a type of white blood cell that discharges toxic substances to destroy invading cells (and, occasionally, host cells). In this process, the immune system identifies the "threat" and deploys cells prepared to fight it. The immune system's elevated level of awareness of and preparation against the antigen reclassifies the substance as an allergen—a considerably more dangerous threat.

Because an allergy only develops after this process, a person allergic to strawberries, for example, will only experience a reaction the next time they eat something containing strawberries. New allergies can pop up at any point in your life.

An immune system on allergies is a little bit like a brain that can't distinguish a piece of lint from a spider: unable to relax, constantly on guard against every potential threat. After initial exposure, the mast cells activated during the sensitization phase are still equipped with allergen-specific antibodies and remain combat-ready, prepared to respond immediately should a second exposure ever occur. If it does—and it probably will—here’s what you can expect to happen.

ALLERGIC REACTION

If two or more allergen molecules bind to a sensitized mast cell, the mast cell releases inflammatory mediators that produce an allergic reaction. These mediators include substances like histamine and more of the interleukins that, in turn, activate eosinophils, Th2 cells, and basophils (another type of white blood cell). In a non-allergic reaction, mediators produce helpful inflammation that prevents infection and initiates healing—but those same symptoms can be annoying and even dangerous when the immune system attacks an otherwise benign allergen. Mast cells also release leukotrienes, which recruit more immune cells to the area and speed up the reaction. That leads to what Stanford University researcher Tina Sindher calls a “‘chain reaction’ of allergic inflammation.”

With the release of histamine, you might experience both bronchial contraction—which makes it more difficult to breathe—and blood vessel dilation. The latter makes it easier for blood to flow to affected areas, but it also makes blood vessels more permeable, allowing blood to escape from the blood vessel walls and flow into the spaces between cells and causing swelling and hives.

For most, these symptoms are merely uncomfortable; they can occur as late as eight to 12 hours after initial exposure, long after the allergen is gone, and can be alleviated with an antihistamine like Benadryl. But for a person with severe allergies, a life-threatening allergic response can occur within minutes: Their airways will constrict so much they won't be able to breathe, and their blood vessels will be unable to contract, which can lead to a drop in a blood pressure and keep veins from getting blood back to the heart. The combination of airway constriction and blood vessel dilation can make it impossible for the body to supply enough oxygen to major organs—that's anaphylactic shock.

The only way to stop anaphylaxis in its tracks is with epinephrine, more commonly known as adrenaline. Adrenaline is a hormone naturally produced by the adrenal glands to help generate the "fight or flight" response in emergency situations. It works by constricting certain blood vessels, increasing blood pressure, and relaxing airways, counteracting all the reactions produced by histamines.

According to Sindher, it’s important to use epinephrine immediately if you're at risk for anaphylactic shock. “There’s a general belief out there that epinephrine should only be used in the worst-case scenario,” she tells Mental Floss. “In fact, most of the complications we see in food allergic reactions are due to delayed use in Epi. Antihistamines can be helpful in treating the symptoms of itching and congestion, but they do not help stop an allergic reaction.”

THE FUTURE OF ALLERGY TREATMENT

Researchers like Sindher are still trying to understand what causes allergies, and why the prevalence of food allergies has increased over the past few decades. Sindher’s main goal is to find new ways of treating (and hopefully curing) allergies. The most established technique (for food allergies, at least) is oral immunotherapy, where allergic individuals gradually eat more of their allergen until they can have small amounts without experiencing a reaction. That’s usually done extremely gradually, over the course of months or years, and always under the supervision of a certified allergist.

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Sindher says scientists are still testing other types of immunotherapy treatments and vaccinations in clinical trials: “A lot of research is going into trying to identify the causes so we can be successful in the prevention as well as treatment of food allergies.”

Until that happens, though, doctors say the best course of action is to be careful around allergens. Medications are useful and necessary, but prevention is the name of the game when it comes to allergies.

12 Facts About the Gallbladder

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Don't feel too bad if you forgot you have a gallbladder—it's one of those body parts that people tend to ignore unless there's a problem. Here's a refresher: It's that small pouch beneath the liver whose primary function is to store bile, which helps you digest fats. So the next time you wolf down a Quarter Pounder with cheese, you can thank your gallbladder for doing its part. Here are a few other things you should know.

1. IT’S THE SIZE OF A SMALL PEAR, AND IT LOOKS LIKE ONE, TOO.

Right before you take your first bite of pizza, your gallbladder is full of bile—an alkaline fluid that's produced in the liver, transported to the gallbladder, and then released into the small intestine to help break down fat and bilirubin, a product of dead red blood cells. The organ can hold the equivalent of a shot glass of the yellow-green liquid, which causes it to swell up to the size of a small pear.

When you eat certain foods—especially fatty ones—the gallbladder releases the bile and deflates like a balloon. Although most gallbladders are roughly 1 inch wide and 3 inches long, there are notable exceptions. In 2017, a gallbladder removed from a woman in India measured nearly a foot long, making it the longest gallbladder in the world.

2. YOU CAN LIVE WITHOUT IT.

You don’t need your gallbladder to live a full and healthy life. Just ask British playwright Mark Ravenhill, who wrote an account for the BBC about getting his gallbladder removed after a gallstone—a solid object made of cholesterol or calcium salts and bilirubin—had moved painfully into his pancreas. "'The gallbladder's completely useless,'" Ravenhill recalled his doctor explaining. "'If it's going to be a problem, best just to take it out.'"

In addition to preventing more gallstones from forming, a physician may recommend that a patient’s gallbladder be removed due to other diseases, like cholecystitis (inflammation of the gallbladder) and cancer. In most cases, removing it doesn’t affect digestion, but there can be some complications. "People can certainly live without one, but they do have to watch their fat intake," says Ed Zuchelkowski, an anatomist and biology professor at California University of Pennsylvania. People who don't have gallbladders still produce bile, but it flows directly from the liver to the small intestine. The only difference is that "you would not have as much bile readily available to release," Zuchelkowski tells Mental Floss, which could cause minor problems like diarrhea if you're eating fatty foods.

3. OUR HUNTER-GATHERER ANCESTORS MAY HAVE NEEDED IT MORE THAN WE DO.

"[The gallbladder] probably was more important to people in days when they would eat fewer meals and larger meals," Zuchelkowski says. This was generally the situation that our hunter-gatherer ancestors found themselves in. As Ravenhill notes, "feast or famine was the general rule." Nomadic groups ate large slabs of meat about once a week, and the gallbladder helped to quickly digest the onslaught of protein and fat.

Even though our diets and eating habits have changed drastically since then, evolution hasn't caught up—we still have the same digestive system. It's probably for this reason that "most meat-eating animals have a gallbladder," Zuchelkowski says. "Dogs do, cats do—they can concentrate bile just like we do, but I think you’d find that in animals that only eat vegetation, that’s where it’s likely to be missing.” However, Zuchelkowski notes that the gallbladder also helps you absorb fat-soluble vitamins like A, D, E, and K, so it still serves a useful function in people who are vegetarians.

4. ASTRONAUTS ARE ENCOURAGED TO GET THEIRS REMOVED.

A 2012 report from the Canadian Journal of Surgery recommended that astronauts consider having their appendix and gallbladder removed—even if their organs are perfectly healthy—to prevent appendicitis, gallstones, or cholecystitis from setting in when they’re far, far away from Earth's hospitals. “The ease and safety of surgical prophylaxis currently appears to outweigh the logistics of treating either acute appendicitis or cholecystitis during extended-duration space flight,” the authors wrote.

5. ALEXANDER THE GREAT LIKELY DIED FROM A GALLBLADDER GONE BAD.

Alexander may have been great at conquering entire empires, but his organs weren’t exactly up to the task. The king of Macedonia died at the age of 34, and some historians believe that the cause was peritonitis (inflammation of the peritoneum, the tissue lining the abdomen), which itself was a result of acute cholecystitis. “Historians have suggested that the fatal biliary tract disease was fueled by excess consumption of alcohol and overeating at a banquet that Alexander threw for his leading officers in Babylon,” author Leah Hechtman writes in Clinical Naturopathic Medicine.

6. THE DOCTOR WHO CONDUCTED THE FIRST SUCCESSFUL GALLSTONE REMOVAL SURGERY DIDN'T KNOW WHAT HE WAS LOOKING FOR.

Gallbladder-related ailments have been afflicting humans for thousands of years, as evidenced by gallstones found in Egyptian mummies. And for thousands of years, people put up with it because they didn’t know what was wrong or how to fix it. In fact, it wasn’t until 1867 that the first cholecystotomy (removal of gallstones) was carried out. The surgery was performed by Dr. John S. Bobbs of Indianapolis, who had no idea what ailed his patient, 31-year-old Mary Wiggins, until he cut open a sac that he later realized was her gallbladder and “several solid bodies about the size of ordinary rifle bullets” fell out, according to The Indianapolis Star. Amazingly, Wiggins survived and lived to the age of 77. Fifteen years after this surgery, the first cholecystectomy (removal of the gallbladder) was performed in Germany.

7. THE WORLD RECORD FOR MOST GALLSTONES EVER REMOVED FROM A PERSON'S BODY STANDS AT MORE THAN 23,000.

Unlike the Guinness World Record for most Twinkies devoured in one sitting, this isn’t the kind of record you’d enjoy setting. In 1987, an 85-year-old woman complaining of severe abdominal pain showed up at Worthing Hospital in West Sussex, England, and doctors found a shockingly high number of gallstones—23,530, to be exact. In May 2018, a similar (albeit less severe) case of gallstones was reported in India, where a 43-year-old man underwent surgery to have thousands of them removed. “Usually we get to see two to 20 stones, but here there were so many and when we counted them, it was a whopping 4100,” the surgeon told Fox News.

8. SOME EASTERN CULTURES BELIEVE THERE’S A LINK BETWEEN THE GALLBLADDER AND HEADACHES.

Some practitioners of Eastern medicine—especially Traditional Chinese Medicine (TCM)—purport that gallbladder problems can cause certain kinds of headaches. TCM practitioners say our internal organs are connected to channels called meridians, which direct several fundamental substances—like blood, other bodily fluids, and qi (vital life energy)—throughout the body. The gallbladder meridian, for instance, runs along the side of the head near the temple. Through the practice of acupuncture, tiny needles are inserted into the skin along the gallbladder meridian in an effort to relieve tension and free up blocked qi. (Western scientists tend to disagree on what, if any, benefit acupuncture offers.)

9. IN CHINA, BOLD PEOPLE ARE SAID TO HAVE A “BIG GALLBLADDER.”

Speaking of China, the country's primary language, Mandarin, hints at a link between organ function and personality. For instance, a word that’s assigned to bold and daring people translates to “big gallbladder,” and brave people are said to have “gallbladder strength,” according to The Conceptual Structure of Emotional Experience in Chinese. The word for coward, on the other hand, translates to “gallbladder small like mouse.” (Interestingly, mice do in fact have gallbladders, but rats don’t.)

10. WESTERN PHILOSOPHERS ALSO THOUGHT ONE'S TEMPERAMENT HAD TO DO WITH THE GALLBLADDER.

You may remember learning something about the four humors during a high school lesson on ancient Greece. The theory, originating with Hippocrates, held that a person’s temperament was influenced by one of four bodily fluids: black bile, yellow bile, phlegm, and blood. Yellow bile, stored in the gallbladder, was said to make people choleric, or irritable. Disease was blamed on an imbalance of these four humors, and this remained a popular theory up until the 18th century. Because of this theory's longstanding influence, the word gall—a synonym for bile—also meant “embittered spirit” during medieval times. It wasn’t until 1882 that the word took on the meaning of "impudence" or "boldness" in American English—as in “I can’t believe he had the gall to finish that Netflix series without me.”

11. ANCIENT ETRUSCANS USED THEM FOR DIVINATION.

Well, not human gallbladders. Ancient Etruscans, a group of people who once lived in present-day Tuscany and whose civilization became part of the Roman empire, practiced a type of divination called haruspicy. The soothsayers were called haruspices (literally “gut gazers”), and they looked for clues from the gods in the markings, coloring, and shape of a sacrificial sheep’s liver and gallbladder. This was often done before the Romans went into battle, but the practice was never adopted as part of the state religion.

12. SOME GALLBLADDERS SPORT A PHRYGIAN CAP.

A crease called a "Phrygian cap" at the base of the gallbladder occurs in about 4 percent of people. Its odd name is something of a misnomer. It comes from its resemblance to a type of peaked felt hat called a pileus, worn by emancipated slaves in ancient Rome; the design was similar to the peaked caps then worn in Phrygia, a region in modern-day Turkey. Much later, during the French Revolution, people took to wearing Phrygian caps—which they likely confused with the pileus's style—as symbols of their freedom from tyranny. In the 20th century, the Smurfs started wearing them.

As for the aforementioned gallbladder abnormality, there’s no deeper symbolism in its name. The way it folds over just looks a lot like a Phrygian cap. Despite being a “congenital anomaly,” as a 2013 study published in Case Reports in Gastroenterology puts it, the condition typically causes no symptoms or complications.

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