Monday, December 23, 2013

We are all just tubes wrapped in muscle and bone

kw: book reviews, nonfiction, alimentary canal, physiology, lore

The squeamish may wish to avoid eating while reading Gulp: Adventures on the Alimentary Canal by Mary Roach. But that goes for many of her books, particularly Stiff (about cadavers) and Bonk (about sex science). I do intend to hunt down a copy of Packing for Mars.

A large part of Gulp is debunking myths. Such as that the human bite is the most dangerous, in terms of causing infection. That's only likely to be true for the bite of someone accustomed to eating food so rotten it endangers his health. Otherwise the Komodo Dragon holds gets the prize for the riskiest bite. And how about the other end? A gastroenterologist of our acquaintance once said he can do all kinds of cutting inside someone's colon, and it'll heal without infection or even a scar. He said he seldom needs to prescribe antibiotics. I've seen the followup colonoscopies after having part of my colon removed, and the trimmed end fitted to re-attach to the ileum, which is something like one-third its diameter. The "fitting" section, called an anastomosis, is a smooth taper from big tube to small tube. My intestinal flora didn't cause any trouble during healing.

OK, that paragraph is about 20% upper GI, and 80% lower GI, just like the book. The mouth gets a couple of chapters, saliva one by itself, the stomach two, the ileum (small intestine) just one, and about 8 chapters dwell on the colon, rectum and anus, plus "gas". This is particularly because of the many uses to which our lower GI is put. You'll just love learning how cell phones get smuggled into prisons… or the recreational uses of the rectum and nearby parts.

Recreation aside, the book is very well researched. The author traveled and interviewed and studied. For the macabre end of things, she discusses some of the exhibits of the Mütter Museum in Philadelphia, including a "megacolon" 29 inches in circumference (over 9" diameter; a normal colon maxes out at about 3" diam at the cecum). This is caused by a nerve problem that prevents peristalsis, so the colon won't empty without extreme measures: lots of enemas. Most sufferers die young, Elvis included. She also visited the Restaurant of the Future at the University of Utrecht, the Netherlands. They study chewing. You know that business about chewing 32 times, to do a thorough job, or "Fletcherizing" (chewing each bite for several minutes; you spend all day chewing), to do a thoroughly obsessive job? Neither is needed for proper digestion. Chewing mixes sufficient saliva with the food so it'll go down. Experiments with barely moistened, swallowed chunks found they digested just fine. However, chewing is pleasurable for most of us, such that people who have esophagus damage and must eat by putting macerated food into a tube that enters the stomach through a fistula never feel they've eaten, and are continually famished, regardless how much they stuff through the tube!

Just as studies of "abnormal psychology" help us understand "normal psychology" (I prefer the terms less-usual and more-usual psychology), studies of pathology all along our bodily canal tend to focus on the unusual so as to illuminate the usual. The very few people who have literally eaten themselves to death had to overcome a series of bodily mechanisms that make it harder and harder to keep eating, long before we are in physical danger of bursting our innards. But it has been done, usually by first consuming barbiturates to numb the inner nerves. A clue to the unwary: don't go to a buffet line just after taking medicine that might numb your stomach's defense mechanisms! A paragraph or two on those performers who eat things like broken glass or a chopped-up piano would have been right at home in this chapter, but no go.

Among the major animal groups, we vertebrates are deuterostomes, a term meaning "two mouths". Ms Roach reminds us to be thankful we are not monostomatic like sea anemones, which must defecate back through their mouth, as their body cavity has only one opening. The same goes for all corals and jellyfish and similar critters. Our body plan is essentially a tube wrapped in muscle, enclosed in bone, with skin over all. Insects and relatives such as lobsters differ from vertebrates primarily in having no skin over their bones (it is just inside), and in being "upside down", with the main nerve chord (equal to our spinal chord) along their front side, and the alimentary canal more to the back.

Seeing as how I typically read if I am eating alone, I scheduled reading time away from the table, and read other things (such as Wired or Scientific American) at mealtimes. Much of the book is actually not icky at all, but you never know when turning the page might unleash a surprise. But Ms Roach's surprises are laced with gentle humor. Like a good meal, it left me wanting more.

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