There are nicer things in life than lying on an examining table at the doctor’s with one thermometer in your mouth and another in your behind. But that used to be the standard examination in cases of suspected appendicitis. A significantly higher temperature down below than in the mouth was a major indication. Modern doctors no longer need to rely on temperature differences to diagnose appendicitis. Important symptoms are fever in combination with pain below and to the right of the belly button (the position of the appendix in most people).

Often, pressing that side of the lower abdomen will cause pain, while, curiously, pressing the other side will relieve it. As soon as pressure on the left-hand side is released—ouch! This is because our abdominal organs are surrounded by a supporting fluid. When pressure is applied to the left-hand side, extra support fluid is pushed over to the right, where it provides additional cushioning for the inflamed gut, which relieves pain. Other signs of appendicitis are pain when raising the right leg against a resistant pressure (get someone to push against it), lack of appetite, and nausea.

Our appendix, officially known as the vermiform, or worm-shaped, appendix, has a reputation for being useless. Looking like a deflated balloon of the kind children’s party entertainers twist into animal shapes, the appendix is not only too small to deal with chyme, it is also positioned in a location that partly digested food hardly ever reaches. It is just below the junction between the small and large intestines, and is completely bypassed. This is a creature that can only look on from below as the world continues on its way above. Those of you who remember the bumpy landscape in your mouth might have an idea what its true function could be. Although far removed from the rest of its kind, the appendix is part of the tonsillar immune tissue.

Our large intestine takes care of things that cannot be absorbed in the small intestine. For that reason, it does not have the same velvety texture. It would simply be a waste of energy and resources to fill this part of the gut with absorbent villi. Instead, the large intestine is the home of most of our gut bacteria, which can break down the last nutritious substances for us. And our immune system is very interested in these bacteria.

So, the vermiform appendix couldn’t be better placed. It is far enough away so as not to be bothered by all the digestive business going on above it, but close enough to monitor all foreign microbes. Although the walls of the large intestine include large deposits of immune cells, the appendix is made almost entirely of immune tissue. So, if a bad germ comes by, it is surrounded. However, that also means that everything around it can become infected—360-degree, panoramic inflammation, so to speak. If this inflammation causes the appendix to swell, the little tube has problems sweeping itself clean of those bad germs—leading to one of the more than 270,000 appendectomies carried out every year in the United States alone.

However, that is not the only function of the appendix. It leaves only good germs alive and attacks anything it sees as dangerous, and this also means a healthy appendix acts as a storehouse of all the best, most helpful bacteria. This was discovered by American researchers Randal Bollinger and William Parker in 2007. Its practicality comes into play after a heavy bout of diarrhea. That will often flush away many of the typical gut microbes, leaving the terrain free for other bacteria to settle. This should not be left to chance. And this is when, according to Bollinger and Parker, the appendix team steps in and spreads out protectively throughout the entire large intestine.

In most parts of North America and northern Europe, we do not have many pathogens that cause diarrhea. We may pick up a gastrointestinal flu bug every now and then, but our environment teems with much less dangerous microbes than in India or Spain, for example. So you could say that we do not need our appendix as urgently as the people in those regions. That means no one in areas with few diarrhea-inducing pathogens who has undergone an appendectomy, or is about to face one, should be too worried. The immune cells in the rest of the large intestine may not be quite so closely packed, but in total, they are many times more numerous than those in the appendix, and they are competent enough to take on the job. Anyone who wants to take no chances after a bout of diarrhea can buy good bacteria at the pharmacy to repopulate their gut.

So now, I hope, it is clear why we have an appendix. But what’s the purpose of the large intestine that it is appended to? Nutrients have already been absorbed, there are no villi here, and what does our gut flora want with indigestible leftovers anyway? Our large intestine does not wind about like its smaller counterpart. It surrounds our small intestine on the outside, like a plump picture frame. And it would not take exception to being called plump—it simply needs more room to do its job.

“Waste not, want not” may sound hackneyed today, but for past generations it was a way to survive lean times. And it is also the motto of our large intestine. It takes its time with all the leftovers and digests them thoroughly. The small intestine can get on with processing the next meal, or even the next two, in the meantime, without affecting the large intestine’s work. It doggedly processes leftovers for sixteen hours or so. In doing so, it makes available substances that would have been lost if the gut were more hurried. They include important minerals like calcium, which can only be absorbed properly here. The careful cooperation of the large intestine and its flora also provides us with an extra helping of energy-rich fatty acids, vitamin K, vitamin B12, thiamine (vitamin B1), and riboflavin (vitamin B2). Those substances are useful for many things—for example, to help our blood clot properly, to strengthen our nerves, or to prevent migraines. In the final three feet or so (about the last meter) of the large intestine, our water and salt levels are finely tuned. Not that I’m recommending a taste test, but the saltiness of our feces always remains the same. This fine-balancing act saves the body an entire quart (or liter) of fluids, which we would have to make up by drinking that much more per day.

As with the small intestine, all the treasures absorbed by the large intestine are transported first to the liver for checking, before entering the main blood system. The final few inches (or centimeters) of the large intestine, however, do not send their blood to the detoxifying liver; blood from their vessels goes straight into the main circulatory system. This is because, generally, nothing more is absorbed in this section, simply because everything useful has already been removed. But there is one important exception: any substances contained in a medical suppository. Suppositories can contain much less medication than pills and still take effect more quickly. Tablets and fluid medications often have to contain large doses of the active agent because much of it is removed by the liver before it even reaches the area of the body it is meant to act on. That is, of course, less than ideal, since the substances recognized by the liver as toxins are the reason we take the medicine in the first place. So, if you want to do your liver a favor and still need to take fever-reducing or other medication, make use of the shortcut via the rectum and use a suppository. This is an especially good idea for very young or very old patients.

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