8 Surprising Facts About the Stomach

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.

While you may only think of your stomach when you're eating or it catches your attention with a gurgle or burble, it's much more than a repository for the food you eat. Your stomach kills microbes, secretes hormones and mucus, and absorbs nutrients. Here are eight gut-clenching facts you might not have known:

1. IT HAS SOME SERIOUS STORAGE CAPACITY.

Your stomach at rest holds about 7 ounces of stomach acid and bile. However, it has the capacity to hold nearly a half-pound of food at a time if necessary. (The average capacity is about 32 ounces, or a quarter-gallon.) It normally takes from four to six hours to digest one meal, so this capacity can be important.

2. PH BALANCE AND MUCUS PREVENT ACID FROM CORRODING YOUR STOMACH.

"Thanks to the high production of hydrochloric acid, which is highly potent, the stomach regenerates its lining frequently," says Sydney Ziverts, a health and nutrition investigator for ConsumerSafety.org. The stomach cavity has a powerful protective process in place that normally keeps the pH of the stomach balanced. Potassium ions help to modulate the hydrochloric acid, and the stomach lining itself produces high numbers of goblet mucus cells to protect the lining.

3. IT ALLOWS YOU TO ABSORB THE CRUCIAL VITAMIN B12 OUT OF YOUR FOOD.

Your stomach is responsible for helping to release the crucial vitamin B12 [PDF] from the proteins you eat. Hydrochloric acid and an enzyme called pepsin break the locked B12 out of its protein so it can be absorbed into your blood stream. "The metabolism of vitamin B starts in the stomach in the parietal cells," Lisa Ganjhu, associate professor of gastroenterology and hepatology at NYU Langone Medical Center, tells Mental Floss. Vitamin B "is one of the main vitamins in our body to help with metabolism and energy production," she says.

4. IT'S A HORMONE-GENERATING MACHINE.

Eating and digesting your food is most likely something you never have to think about. Yet your GI tract is home to a veritable orchestra of hormones stimulated by epithelial cells that line the stomach and small intestine. These hormones engage in a wide range of functions, including stimulating appetite, encouraging the secretion of enzymes and gastric acid, and reminding the gall bladder to contract and empty. These hormones directly enter the blood, and eventually affect the function of other parts of the digestive system, including the liver and pancreas, and even your brain.

5. YOUR STOMACH IS ONE OF YOUR IMMUNE SYSTEM'S FIRST LINES OF DEFENSE.

Besides just digesting your food, the stomach helps protect your entire body. "The acidity in our stomach helps to sterilize whatever you're eating. It kills off bacteria and potential food toxins," says Ganjhu. Your gastrointestinal tract also has patches of lymphoid defense cells it sends out when something makes it through the stomach, such as a virus or bacterial infection.  

6. AND IT MAY PLAY A PART IN YOUR MOOD, TOO.

Your stomach may very well be a key player in keeping your mood balanced. New research suggests links between the gut microbiome—the microorganisms that live in any environment—and your mental health. A recent study in the Journal of Psychiatric Research found that transferring the gut microbiota of depressed human patients into rats induced depressive symptoms in the rodents, opening up a whole new realm of possible bacteria-based treatments.

7. STOMACH FLU ISN'T ACTUALLY A FLU.

If you've ever had the misfortune to find yourself stranded by the toilet for 24 to 48 hours purging the contents of your stomach, you may have described the cause as a stomach flu. However, actual influenza is primarily a respiratory infection. What keeps you in the bathroom is likely some form of norovirus or rotavirus, which causes gastroenteritis of the stomach and intestines, and usually resolves in one to two days.

8. THE MOST COMMON CAUSE OF STOMACH ULCERS IS LIKELY BACTERIAL.

The causes of ulcers have perplexed medical researchers for years. However, recent studies have found a link between the bacteria H. pylori and inflammation of the stomach lining, gastritis, and ulcers. In fact, new research suggests that the bacteria may also be linked to stomach cancer.

25 Amazing Facts About the Human Body

iStock.com/kali9
iStock.com/kali9

The human body is an amazing piece of machinery—with a few weird quirks.

  1. It’s possible to brush your teeth too aggressively. Doing so can wear down enamel and make teeth sensitive to hot and cold foods.

  2. Goose bumps evolved to make our ancestors’ hair stand up, making them appear more threatening to predators.

Woman's legs with goosebumps
iStock.com/MyetEck
  1. Wisdom teeth serve no purpose. They’re left over from hundreds of thousands of years ago. As early humans’ brains grew bigger, it reduced space in the mouth, crowding out this third set of molars.

  2. Scientists aren't exactly sure why we yawn, but it may help regulate body temperature.

  3. Your fingernails don’t actually grow after you’re dead.

  4. If they were laid end to end, all of the blood vessels in the human body would encircle the Earth four times.

  5. Humans are the only animals with chins.

    An older woman's chin
    iStock.com/mhelm3011
    1. As you breathe, most of the air is going in and out of one nostril. Every few hours, the workload shifts to the other nostril.

    2. Blood makes up about 8 percent of your total body weight.

    3. The human nose can detect about 1 trillion smells.

    4. You have two kidneys, but only one is necessary to live.

    5. Belly buttons grow special hairs to catch lint.

      A woman putting her hands in a heart shape around her belly button
      iStock.com/PeopleImages
      1. The satisfying sound of cracking your knuckles comes from gas bubbles bursting in your joints.

      2. Skin is the body’s largest organ and can comprise 15 percent of a person’s total weight.

      3. Thumbs have their own pulse.

      4. Your tongue is made up of eight interwoven muscles, similar in structure to an elephant’s trunk or an octopus’s tentacle.

      5. On a genetic level, all human beings are more than 99 percent identical.

        Identical twin baby boys in striped shirts
        iStock.com/BorupFoto
        1. The foot is one of the most ticklish parts of the body.

        2. Extraocular muscles in the eye are the body’s fastest muscles. They allow both of your eyes to flick in the same direction in a single 50-millisecond movement.

        3. A surgical procedure called a selective amygdalohippocampectomy removes half of the brain’s amygdala—and with it, the patient’s sense of fear.

        4. The pineal gland, which secretes the hormone melatonin, got its name from its shape, which resembles a pine nut.

        5. Hair grows fast—about 6 inches per year. The only thing in the body that grows faster is bone marrow.

          An African-American woman drying her hair with a towel and laughing
          iStock.com/GlobalStock
          1. No one really knows what fingerprints are for, but they might help wick water away from our hands, prevent blisters, or improve touch.

          2. The heart beats more than 3 billion times in the average human lifespan.

          3. Blushing is caused by a rush of adrenaline.

12 Intriguing Facts About the Intestines

When we talk about the belly, gut, or bowels, what we're really talking about are the intestines—long, hollow, coiled tubes that comprise a major part of the digestive tract, running from the stomach to the anus. The intestines begin with the small intestine, divided into three parts whimsically named the duodenum, jejunum, and ileum, which absorb most of the nutrients from what we eat and drink. Food then moves into the large intestine, or colon, which absorbs water from the digested food and expels it into the rectum. That's when sensitive nerves in your rectum create the sensation of needing to poop.

These organs can be the source of intestinal pain, such as in irritable bowel syndrome, but they can also support microbes that are beneficial to your overall health. Here are some more facts about your intestines.

1. The intestines were named by medieval anatomists.

Medieval anatomists had a pretty good understanding of the physiology of the gut, and are the ones who gave the intestinal sections their names, which are still used today in modern anatomy. When they weren't moralizing about the organs, they got metaphorical about them. In 1535, the Spanish doctor Andrés Laguna noted that because the intestines "carry the chyle and all the excrement through the entire region of the stomach as if through the Ocean Sea," they could be likened to "those tall ships which as soon as they have crossed the ocean come to Rouen with their cargoes on their way to Paris but transfer their cargoes at Rouen into small boats for the last stage of the journey up the Seine."

2. Leonardo da Vinci believed the intestines helped you breathe.

Leonardo mistakenly believed the digestive system aided respiratory function. In 1490, he wrote in his unpublished notebooks, "The compressed intestines with the condensed air which is generated in them, thrust the diaphragm upwards; the diaphragm compresses the lungs and expresses the air." While that isn't anatomically accurate, it is true that the opening of the lungs is helped by the relaxation of stomach muscles, which does draw down the diaphragm.

3. Your intestines could cover two tennis courts ...

Your intestines take up a whole lot of square footage inside you. "The surface area of the intestines, if laid out flat, would cover two tennis courts," Colby Zaph, a professor of immunology in the department of biochemistry and molecular biology at Melbourne's Monash University, tells Mental Floss. The small intestine alone is about 20 feet long, and the large intestine about 5 feet long.

4. ... and they're pretty athletic.

The process of moving food through your intestines requires a wave-like pattern of muscular action, known as peristalsis, which you can see in action during surgery in this YouTube video.

5. Your intestines can fold like a telescope—but that's not something you want to happen.

Intussusception is the name of a condition where a part of your intestine folds in on itself, usually between the lower part of the small intestine and the beginning of the large intestine. It often presents as severe intestinal pain and requires immediate medical attention. It's very rare, and in children may be related to a viral infection. In adults, it's more commonly a symptom of an abnormal growth or polyp.

6. Intestines are very discriminating.

"The intestines have to discriminate between good things—food, water, vitamins, good bacteria—and bad things, such as infectious organisms like viruses, parasites and bad bacteria," Zaph says. Researchers don't entirely know how the intestines do this. Zaph says that while your intestines are designed to keep dangerous bacteria contained, infectious microbes can sometimes penetrate your immune system through your intestines.

7. The small intestine is covered in "fingers" ...

The lining of the small intestine is blanketed in tiny finger-like protrusions known as villi. These villi are then covered in even tinier protrusions called microvilli, which help capture food particles to absorb nutrients, and move food on to the large intestine.

8. ... And you can't live without it.

Your small intestine "is the sole point of food and water absorption," Zaph says. Without it, "you'd have to be fed through the blood."

9. The intestines house your microbiome. 

The microbiome is made up of all kinds of microorganisms, including bacteria, viruses, fungi, and protozoans, "and probably used to include worm parasites too," says Zaph. So in a way, he adds, "we are constantly infected with something, but it [can be] helpful, not harmful."

10. Intestines are sensitive to change.

Zaph says that many factors change the composition of the microbiome, including antibiotics, foods we eat, stress, and infections. But in general, most people's microbiomes return to a stable state after these events. "The microbiome composition is different between people and affected by diseases. But we still don't know whether the different microbiomes cause disease, or are a result in the development of disease," he says.

11. Transferring bacteria from one gut to another can transfer disease—or maybe cure it.

"Studies in mice show that transplanting microbes from obese mice can transfer obesity to thin mice," Zaph says. But transplanting microbes from healthy people into sick people can be a powerful treatment for some intestinal infections, like that of the bacteria Clostridium difficile, he adds. Research is pouring out on how the microbiome affects various diseases, including multiple sclerosis, Parkinson's, and even autism.

12. The microbes in your intestines might influence how you respond to medical treatments.

Some people don't respond to cancer drugs as effectively as others, Zaph says. "One reason is that different microbiomes can metabolize the drugs differently." This has huge ramifications for chemotherapy and new cancer treatments called checkpoint inhibitors. As scientists learn more about how different bacteria metabolize drugs, they could possibly improve how effective existing cancer treatments are.

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