Poop Partnership

Eat something right now. Go ahead—I won’t judge!

Now, let’s think about what happens next. You’ve already chewed the food up well, and your mouth mixed some saliva in with the food. This process is called mastication (minds, out of the gutter, please), from the Greek to chew.

Your throat kind of grabs onto the food next, doesn’t it? Feel what happens when you swallow. Your tongue pushes everything into your esophagus, where slow waves of electrical activity propagate along a long tube of muscles. Each little section fires, one after the other, helping to squish the food down that tube.

Those same pseudo-medical ancient Greeks who named mastication also named this process, and they called it peristalsis. Peri- is the same root as perimeter, and it means around, while stalsis is more like to constrict. This perfectly describes what’s happening here: everything is getting squished around the food as it goes down, kind of like massaging a marble through an uninflated balloon.

Your stomach is always ready for this little squished nugget when it arrives. Here, those stomach acids I heard so much about in 1980s Tums ads do their magic, mixing with those food nuggets and kind of stirring them around until they become like a paste called chyme.

From here, the chyme enters the small intestine, using that same peristalsis balloon-marble trick to keep the food moving along the long tube inside you. Here, the nutrients are slurped out of the chyme by more chemical reactions.

Juice from your pancreas helps to break down fats, carbs, and proteins. Meanwhile, your liver adds bile to the mix, which causes any big clumps of fat to break up into smaller pieces. This emulsifies the fat into the chyme mixture, kind of like a vinaigrette dressing or butter.

A lot of the water is absorbed, along with plenty of vitamins and minerals your body needs. Then, the chyme reaches your large intestine, where the real magic happens.

This is where your partnership with another species really comes into play. Here, a trillion individual bacteria, all living inside your gut, spring into action. Your gut microbiome is made up of around ten times more cells than make up your entire body, so in one sense you’re more bacteria than human, but of course our partnership with bacteria very much makes us who we are.

Those tiny, friendly warriors instantly go to battle on the chyme, slurping away any remaining nutrients and water. These critters… well, there is no delicate way to say this: they eat your poop, and then you poop them out.

Poop is largely a structured bacteria pile, in a way.

There’s a bit more going on in your small intestine, too. Think about it from the perspective of the bacteria, who live for generation after generation inside your gut.

Although bacteria are living entities that multiply rapidly, they need a substrate in order to keep going. In other words, they need to use materials from their surroundings in order to create more of themselves.

These gut bacteria do just that, and they use what is all around them for this purpose: you. In particular, they use your large intestine, which we have to admit is pretty convenient for them.

So, in a weird sense, non-life becomes life inside your body. Little soldiers are formed from a tiny amount of bacteria already in there, but they are all made of stuff from your intestine. Then, these entities go to work on processing the stuff that’s going to make the next generation of bacteria to live inside you, all the while reproducing and making more versions of themselves from you.

There’s an awful lot of wonder in biology, and I find so much awe in poop in particular. Today marks the tenth piece I’ve written on the subject, and you can see the other nine here.

Today, let’s think about this poop partnership a bit, although you might want to finish whatever you’re eating first.