Each individual villus contains a tiny blood vessel—a capillary—that is fed with the absorbed molecules. All the small intestine’s blood vessels eventually come together and carry the blood to the liver, where the nutrients are screened for harmful substances and toxins. Any dangerous substances can be destroyed here before the blood passes into the main circulatory system. If we eat too much, this is where the first energy stores are created. The nutrient-rich blood then flows from the liver directly to the heart. There, it receives a powerful push and is pumped to the countless cells of our body. In this way, a sugar molecule can end up in a skin cell in your right nipple, for example, where it is absorbed and then “burned” along with oxygen. That releases energy, which the cell uses to stay alive, with heat and tiny amounts of water created as byproducts. This happens inside so many cells at the same time that the heat produced keeps our body at a constant temperature of 97 to 99 degrees Fahrenheit (36 to 37 degrees Celsius).
The basic principle underlying our energy metabolism is simple. Nature requires energy to ripen an apple on the tree. We humans come along and break the apple down into its constituent molecules and metabolize them for energy. We then use the energy released to keep us alive. All the organs that develop out of that embryonic gut tube are able to provide fuel for our cells. Our lungs, for example, do nothing other than absorb molecules with every breath we take. Thus, “breathing in” really means “taking in nourishment in gaseous form.” A good proportion of our body weight is made from such inhaled atoms and not from cheeseburgers. Indeed, plants draw the majority of their weight from the air and not from the soil they grow in . . . I hope I haven’t just inadvertently provided the next dubious diet idea to appear in women’s magazines!
So, all our body’s organs use up energy, but it is from the small intestine that we start to get some energy back. That explains why eating is such a pleasant pastime. However, we can’t expect to feel a burst of energy as soon as we have swallowed the last mouthful of a meal. In fact, many people find they feel tired and sluggish after eating. The food has not yet reached the small intestine—it is still in the preparatory stages of digestion. We no longer feel hungry because our stomach has been expanded by the food we’ve eaten. But we feel just as sluggish as we did before the meal, and now we have to come up with the extra energy for all that mixing and breaking down. To achieve this, a large amount of blood is delivered to our digestive organs, and many researchers also believe that postprandial tiredness may be due to the resulting reduced blood supply to the brain.
One of my professors always dismissed that idea, arguing that if all the blood in our head were diverted to our stomach we would be dead, or at least unconscious. Indeed, there are other possible causes of the fatigue that follows eating. Certain messenger chemicals released by the body when we are full can also stimulate the areas of the brain responsible for tiredness. This tiredness is perhaps inconvenient for our brain when we are at work, but the small intestine welcomes it. It works most effectively when we are pleasantly relaxed. It means the optimum amount of energy is available for digestion and our blood is not full of stress hormones. The phlegmatic after-lunch reader is a more efficient digester than the stressed-out office executive.
The Unnecessary Appendix
and the Bulgy Large Intestine
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.
&n
bsp; “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.
What We Really Eat
THE MOST IMPORTANT phase of our digestion takes place in the small intestine, where the maximum surface area meets the maximum reduction of our food down to the tiniest pieces. This is where the decisions are made. Can we tolerate lactose? Is this food good for our health? Which food causes allergic reactions? Here, in this final stage of breakdown, our digestive enzymes work like tiny pairs of scissors. They snip away at our food until it shares a lowest common denominator with our cells. Canny as ever, Mother Nature here makes use of the fact that all living things are made out of the same basic ingredients: sugar molecules, amino acids, and fats. Everything we eat comes from living things—at this biological level, there is no difference between an apple, a tree, and a cow.
Sugar molecules can be linked to form complex chains. When that happens, they no longer taste sweet, and we know them as the carbohydrates we find in bread, pasta, or rice. After that piece of toast you ate for breakfast has undergone the snipping of the enzyme scissors, the final product is the same number of sugar molecules as a couple of spoonfuls of refined household sugar. The only difference is that household sugar does not require so much work from our enzymes as it is already broken down into such small pieces when it arrives in the small intestine that it can be absorbed directly into the bloodstream. Eating too much pure sugar at once really does make our blood sweeter for a while.
The sugar contained in white toast is digested relatively quickly by our enzymes. With wholegrain bread, everything moves at a much more leisurely pace. Such bread contains particularly complex sugar chains, which have to be broken down bit by bit. So, wholegrain bread is not a sugar explosion, but a beneficial sugar store. Incidentally, our body has to work much harder to restore a healthy balance if a sugar onrush comes suddenly. It pumps out large amounts of various hormones, most importantly insulin. The result is that we rapidly feel tired again once this special operation is over. If it doesn’t enter the system too quickly, sugar is an important raw material for our body. It is used as fuel for our cells—like heat-giving firewood—or to build sugar structures for use in our body, such as the antler-like glycocalyxes attached to our gut cells.
Despite the problems, our body loves sugary sweet treats because they save the body work, since sugar can be taken up more quickly. The same is true of warm proteins. In addition, sugar can be turned into energy extremely quickly, and our brain rewards us for a rush of rapid energy by making us feel good. However, there is one problem: never before, in the history of humankind, have we been faced with such a huge abundance of readily available sugar. Some 80 percent of the processed foods found on the shelves of modern-day American supermarkets contain added sugar. On an evolutionary scale, then, we could say our species has just discovered the secret stash of candies at the back of the cupboard, and it keeps returning to binge on the booty before collapsing on the couch with a stomachache and sugar shock.
Even though we know intellectually that too much snacking is bad for us, we can’t really blame our instincts for encouraging us to grab every opportunity for a treat. When we eat too much sugar, our body simply stores it away for leaner times. Quite practical, really. One way the body does this is by relinking the molecules to form long, complex chains of a substance called glycogen, which is then stored in the liver. Another strategy is to convert the excess sugar into fat and store it in fatty tissue. Sugar is the only substance our body can turn into fat with little effort.
Glycogen reserves are soon used up—just about the time during your run when you notice the exercise is suddenly much harder work. That is why nutritional physiologists say we should do at least an hour’s exercise if we want to burn fat. It is not until we pass through that first energy dip that we start to tap into those fine reserves. We might find it annoying that our paunch isn’t the first thing to go, but our body is deaf to such complaints. The simple reason for this is that human cells adore fat.
Fat is the most valuable and efficient of all food particles. The atoms are so cleverly combined that they can concentrate twice as much energy per ounce as carbohydrates or protein. We use fat to coat our nerves—just like the plastic on an electric cable. It is this coating that makes us such fast thinkers. Some of the most important hormones in our body are made out of fat, and every single one of our cells is wrapped in a membrane made largely of fat. Such a special substance must be protected and not squandered at the first sign of physical exertion. When the next period of famine comes—and there have been many over the eons—every ounce of fat in that paunch is a life insurance policy.
Our small intestine also knows the special value of fat. Unlike other nutrients, it cannot be absorbed straight into the blood from the gut. Fat is not soluble in water—it would immediately clog the tiny blood capillaries in the villi of the gut and float on top of the blood in larger vessels, like the oil on spaghetti water. So fat must be absorbed via a different route: the lymphatic system. Lymphatic vessels are to blood vessels as Robin is to Batman. Every blood vessel inside the body is accompanied by a lymphatic vessel, even each tiny capillary in the small intestine. While our blood vessels are thick and red and heroically pump nutrients to our tissues, the lymphatic vessels are thin and filmy white in color. They drain away fluid that is pumped out of our tissue and transport the immune cells, whose job it is to ensure that everything is as it should be throughout the body.
Lymphatic vessels are so slight because they do not have muscular walls like our blood vessels. Often, they work just by using gravity. That explains why we sometimes wake up in the morning with swollen eyes. Gravity is not very much help when you are lying down. The tiny lymphatic vessels in our face are n
icely open, but it is only when we get up and gravity kicks in that the fluid transported there during the night by our blood vessels can flow back down. (The reason our lower legs do not fill up with fluid after a long day on our feet is that our leg muscles squeeze the lymphatic vessels every time we take a step and that squeezes the fluid—known as lymph in medical circles—upwards.) The lymphatic system is seen as an underappreciated weakling everywhere in the body except in the small intestine. This is its time to shine! All the body’s lymph vessels converge in an impressively thick duct, where all the digested fat can gather without the risk of clogging.
It’s well known that doctors like to show off their Latin skills, and they give this vessel the mighty sounding name ductus thoracicus. It sounds almost as if it means to say, “Hail, Ductus! Teach us why noble fat is so important and evil fat so bad!” Shortly after we eat a fatty meal, there are so many tiny fat droplets in our ductus or thoracic duct that the lymph fluid is no longer transparent but milky white. When the fat has gathered, the thoracic duct skirts the belly, passes through the diaphragm, and heads straight for the heart. (All the fluid drained from our legs, eyelids, and gut ends up here.) So, whether it’s extra virgin olive oil or cheap fat from french fries, it all goes straight into the heart—there is no detoxing detour via the liver as there is for everything else we digest.
A = Blood vessels pass through the liver and then go on to the heart. B = Lymphatic vessels go straight to the heart.
Gut: The Inside Story of Our Body's Most Underrated Organ (Revised Edition) Page 4
