11 Facts About the Appendix

Illustration by Mental Floss / Images: iStock
Illustration by Mental Floss / Images: iStock

Despite some 500 years of study, the appendix might be one of the least understood structures in the human body. Here's what we know about this mysterious organ.

1. THE ANCIENT EGYPTIANS CALLED IT THE "WORM" OF THE BOWEL.

The human appendix is small, tube-shaped, and squishy, giving ancient Egyptians, who encountered it when preparing bodies for funerary rites, the impression of a worm. Even today, some medical texts refer to the organ as vermiform—Latin for "worm-like."

2. THE APPENDIX SHOWS UP IN LEONARDO DA VINCI’S DRAWINGS.

The earliest description of a human appendix was written by the Renaissance physician-anatomist Jacopo Berengario da Carpi in 1521. But before that, Leonardo da Vinci is believed to drawn the first depiction of the organ in his anatomical drawings in 1492. Leonardo claimed to have dissected 30 human corpses in his effort to understand the way the body worked from mechanical and physiological perspectives.

3. IT'S ABOUT THE SIZE OF A PINKY FINGER.

The appendix is a small pouch connected to the cecum—the beginning of the large intestine in the lower right-hand corner of your abdomen. The cecum’s job is to receive undigested food from the small intestine, absorb fluids and salts that remain after food is digested, and mix them with mucus for easier elimination; according to Mohamad Abouzeid, M.D., assistant professor and attending surgeon at NYU Langone Health, the cecum and appendix have similar tissue structures.

4. CHARLES DARWIN THOUGHT IT WAS A VESTIGIAL ORGAN …

The appendix has an ill-deserved reputation as a vestigial organ—meaning that it allegedly evolved without a detectable function—and we can blame Charles Darwin for that. In the mid-19th century, the appendix had been identified only in humans and great apes. Darwin thought that our earlier ancestors ate mostly plants, and thus needed a large cecum in which to break down the tough fibers. He hypothesized that over time, apes and humans evolved to eat a more varied and easier-to-digest diet, and the cecum shrank accordingly. The appendix itself, Darwin believed, emerged from the folds of the wizened cecum without its own special purpose.

5. … BUT THE APPENDIX PROBABLY EVOLVED TO HELP IMMUNE FUNCTION.

The proximity and tissue similarities between the cecum and appendix suggest that the latter plays a part in the digestive process. But there’s one noticeable difference in the appendix that you can see only under a microscope. “[The appendix] has a high concentration of the immune cells within its walls,” Abouzeid tells Mental Floss.

Recent research into the appendix's connection to the immune system has suggested a few theories. In a 2015 study in Nature Immunology, Australian researchers discovered that a type of immune cells called innate lymphoid cells (ILCs) proliferate in the appendix and seem to encourage the repopulation of symbiotic bacteria in the gut. This action may help the gut recover from infections, which tend to wipe out fluids, nutrients, and good bacteria.

For a 2013 study examining the evolutionary rationale for the appendix in mammal species, researchers at Midwestern University and Duke University Medical Center concluded that the organ evolved at least 32 times among different lineages, but not in response to dietary or environmental factors.

The same researchers analyzed 533 mammal species for a 2017 study and found that those with appendices had more lymphatic (immune) tissue in the cecum. That suggests that the nearby appendix could serve as "a secondary immune organ," the researchers said in a statement. "Lymphatic tissue can also stimulate growth of some types of beneficial gut bacteria, providing further evidence that the appendix may serve as a 'safe house' for helpful gut bacteria." This good bacteria may help to replenish healthy flora in the gut after infection or illness.

6. ABOUT 7 PERCENT OF AMERICANS WILL GET APPENDICITIS DURING THEIR LIFETIMES.

For such a tiny organ, the appendix gets infected easily. According to Abouzeid, appendicitis occurs when the appendix gets plugged by hardened feces (called a fecalith or appendicolith), too much mucus, or the buildup of immune cells after a viral or bacterial infection. In the United States, the lifetime risk of getting appendicitis is one in 15, and incidence in newly developed countries is rising. It's most common in young adults, and most dangerous in the elderly.

When infected, the appendix swells up as pus fills its interior cavity. It can grow several times larger than its average 3-inch size: One inflamed appendix removed from a British man in 2004 measured just over 8 inches, while another specimen, reported in 2007 in the Journal of Clinical Pathology, measured 8.6 inches. People with appendicitis might feel generalized pain around the bellybutton that localizes on the right side of the abdomen, and experience nausea or vomiting, fever, or body aches. Some people also get diarrhea.

7. APPENDECTOMIES ARE ALMOST 100 PERCENT EFFECTIVE FOR TREATING APPENDICITIS.

Treatment for appendicitis can go two ways: appendectomy, a.k.a. surgical removal of the appendix, or a first line of antibiotics to treat the underlying infection. Appendectomies are more than 99 percent effective against recurring infection, since the organ itself is removed. (There have been cases of "stump appendicitis," where an incompletely removed appendix becomes infected, which often require further surgery.)

Studies show that antibiotics produce about a 72 percent initial success rate. “However, if you follow these patients out for about a year, they often get recurrent appendicitis,” Abouzeid says. One 2017 study in the World Journal of Surgery followed 710 appendicitis patients for a year after antibiotic treatment and found a 26.5 percent recurrence rate for subsequent infections.

8. AN INFECTED APPENDIX DOESN’T ACTUALLY BURST.

You might imagine a ruptured appendix, known formally as a perforation, being akin to the "chestbuster" scene in Alien. Abouzeid says it's not quite that dramatic, though it can be dangerous. When the appendix gets clogged, pressure builds inside the cavity of the appendix, called the lumen. That chokes off blood supply to certain tissues. “The tissue dies off and falls apart, and you get perforation,” Abouzeid says. But rather than exploding, the organ leaks fluids that can infect other tissues.

A burst appendix is a medical emergency. Sometimes the body can contain the infection in an abscess, Abouzeid says, which may be identified through CT scans or X-rays and treated with IV antibiotics. But if the infection is left untreated, it can spread to other parts of the abdomen, a serious condition called peritonitis. At that point, the infection can become life-threatening.

9. SURGEONS CAN REMOVE AN APPENDIX THROUGH A TINY INCISION.

In 1894, Charles McBurney, a surgeon at New York's Roosevelt Hospital, popularized an open-cavity, muscle-splitting technique [PDF] to remove an infected appendix, which is now called an open appendectomy. Surgeons continued to use McBurney's method until the advent of laparoscopic surgery, a less invasive method in which the doctor makes small cuts in the patient's abdomen and threads a thin tube with a camera and surgical tools into the incisions. The appendix is removed through one of those incisions, which are usually less than an inch in length.

The first laparoscopic appendectomies were performed by German physician Kurt Semm in the early 1980s. Since then, laparoscopic appendectomies have become the standard treatment for uncomplicated appendicitis. For more serious infections, open appendectomies are still performed.

10. AN APPENDIX ONCE POSTPONED A ROYAL CORONATION.

When the future King Edward VII of Great Britain came down with appendicitis (or "perityphlitis," as it was called back then) in June 1902, mortality rates for the disease were as high as 26 percent. It was about two weeks before his scheduled coronation on June 26, 1902, and Edward resisted having an appendectomy, which was then a relatively new procedure. But surgeon and appendicitis expert Frederick Treves made clear that Edward would probably die without it. Treves drained Edward's infected abscess, without removing the organ, at Buckingham Palace; Edward recovered and was crowned on August 9, 1902.

11. THE WORLD'S LONGEST APPENDIX MEASURED MORE THAN 10 INCHES.

On August 26, 2006, during an autopsy at a Zagreb, Croatia hospital, surgeons obtained a 10.24-inch appendix from 72-year-old Safranco August. The deceased currently holds the Guinness World Record for "largest appendix removed."

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).

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