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When we refer to the belly, gut, or bowels, we're really talking about the intestines—long, tubular structures that are a key part of the digestive system, extending from the stomach to the anus. The journey begins with the small intestine, divided into three sections humorously named the duodenum, jejunum, and ileum, which absorb most of the nutrients from the food and liquids we consume. Next, food moves into the large intestine, or colon, which absorbs water from the partially digested food and then excretes it into the rectum. That's when the sensitive nerves in your rectum trigger the sensation of needing to poop.
These organs can sometimes cause discomfort, as seen in conditions like irritable bowel syndrome, but they also house beneficial microbes that contribute to your overall health. Here are some more interesting facts about your intestines.
1. The intestines were named by anatomists in the medieval period.
Medieval anatomists had a strong grasp of the gut's physiology and are credited with naming the intestinal sections that are still used in modern anatomy. When not focused on the moral aspects of these organs, they got creative in their descriptions. In 1535, Spanish physician Andrés Laguna noted that since the intestines "transport the chyle and all waste through the entire stomach region as if navigating the Ocean Sea," they could be compared to "the tall ships that, after crossing the ocean, arrive in Rouen with their goods, only to transfer their cargo to smaller boats for the final leg of the journey up the Seine."
2. Leonardo da Vinci believed the intestines were involved in respiration.
Leonardo mistakenly believed that the digestive system contributed to breathing. In 1490, he wrote in his private notes, "The compressed intestines with the condensed air generated within them push the diaphragm upward; this compression of the diaphragm then forces the air out of the lungs." Although this isn't anatomically correct, it's true that the stomach muscles' relaxation aids the lungs' expansion, which in turn helps lower the diaphragm.
3. Your intestines could stretch across two tennis courts ...
Your intestines take up an enormous amount of space inside you. "If the intestines were spread out flat, their surface area would cover two tennis courts," says Colby Zaph, a professor of immunology at Monash University's Department of Biochemistry and Molecular Biology. The small intestine alone stretches to about 20 feet, while the large intestine measures about 5 feet.
4. ... and they're quite athletic.
The movement of food through your intestines relies on a wave-like muscular action called peristalsis, which you can observe in action during surgery in this YouTube video.
5. Your intestines can telescope—but that's something you definitely don't want to happen.
Intussusception is a condition in which a portion of your intestine folds in on itself, typically occurring between the lower part of the small intestine and the start of the large intestine. It often causes severe intestinal pain and requires urgent medical intervention. Though rare, it may be linked to a viral infection in children, while in adults it is more commonly associated with abnormal growths or polyps.
6. Intestines are highly selective.
"The intestines must distinguish between beneficial substances—such as food, water, vitamins, and healthy bacteria—and harmful agents like viruses, parasites, and bad bacteria," Zaph explains. Scientists are still unsure of the exact mechanism behind this process. Zaph adds that while the intestines are meant to trap harmful bacteria, sometimes infectious microbes can sneak past the immune defenses through the intestines.
7. The small intestine is lined with "finger-like" projections ...
The small intestine’s interior is covered in microscopic finger-shaped structures called villi. These villi themselves are topped with even smaller projections known as microvilli, which play a key role in capturing food particles for nutrient absorption, then pushing the remaining food towards the large intestine.
8. ... And it's vital for survival.
The small intestine "is the only area where food and water can be absorbed," Zaph explains. Without it, "you'd need to be nourished through your bloodstream."
9. Your microbiome resides within your intestines.
The microbiome is composed of various microorganisms, such as bacteria, viruses, fungi, and protozoa, "and perhaps even included worm parasites in the past," according to Zaph. He further adds, "we are constantly exposed to something, but it [can be] beneficial rather than harmful."
10. The intestines are highly responsive to changes.
Zaph explains that numerous factors can alter the microbiome, such as antibiotics, diet, stress, and infections. However, most people's microbiomes tend to return to a stable state after these changes. "The microbiome varies between individuals and is influenced by diseases. But we still don't know whether the variations in microbiomes are the cause of diseases or if they are a result of disease development," he states.
11. Transferring gut bacteria from one person to another could transmit a disease—or perhaps even cure it.
"Studies involving mice show that transferring microbes from obese mice can induce obesity in lean mice," says Zaph. However, transplanting microbes from healthy individuals into those suffering from intestinal infections, such as Clostridium difficile bacteria, can serve as a powerful treatment, he explains. Research continues to explore how the microbiome impacts various diseases, including multiple sclerosis, Parkinson's, and even autism.
12. The microbes in your intestines could affect your response to medical treatments.
Zaph mentions that some individuals don't respond to cancer treatments as effectively as others. "One reason is that different microbiomes may metabolize the drugs in distinct ways." This has significant implications for chemotherapy and new cancer treatments, like checkpoint inhibitors. As scientists gain a deeper understanding of how bacteria metabolize drugs, they may be able to improve the effectiveness of existing cancer treatments.
