Gut summary

Let’s admire the work our gut does by tracking a piece of cake as it journeys through the digestive system. This journey actually begins before your first bite. In this case, it begins while you’re standing outside the bakery, and you first lay eyes on that cake.

As you stare at the cake through the shop window, you begin to imagine the sweet aroma and taste, and your mouth begins to water. Unable to resist, you decide to buy it.

Imagine thousands of fans at a sports stadium, all doing the wave. Your esophagus moves in a similar way, with an undulatory motion that eases food from one end to the other. This work is performed automatically and autonomously: once that piece of cake is one-third of the way down your esophagus, you have no control over the muscles that push the food along its journey.

Even if you were to do a handstand, the esophagus would continue moving the food toward the stomach. This is work that your esophagus has mastered: it’s been doing it since you were a baby in your mother’s womb, swallowing half a liter of amniotic fluid every day.

From the esophagus, the piece of cake descends into the stomach. There, the food is processed for about two hours, until it is fully broken up by gastric fluid. At this point, the cake has been broken into pieces approximately 0.2 millimeters in size.

The small intestine is in constant movement. Inside, the walls are made up of intestinal villi, tiny finger-like protrusions that move and manipulate the food as it continues its journey. Each millimeter of the small intestine contains about 30 villi – and they only know one direction: forward!

Tiny electric shocks cause the intestinal muscles to contract in a rhythmical motion, pushing the food along. During this process, digestive fluid, which has extracted the nutrients of the food, is absorbed into the body. One piece of cake would last about an hour in the small intestine before entering the large intestine.

The small intestine likes to keep things tidy. After performing its duty, it goes about cleaning itself up. As it tidies up, it growls.

When you think of allergies, what’s the first part of the body you think of? You probably imagine red, itchy eyes, skin rashes or a runny nose. The gut probably isn’t the first place that comes to mind. Well, this blink might change that.

There’s an interesting theory about the role your gut plays in the allergies you experience.

It begins with how proteins are broken up during the digestive process. Sometimes this doesn’t go as smoothly as it should. Hazelnuts, for example, can leave behind small pieces of protein that don’t get absorbed into the bloodstream when the small intestine is doing its work.

Have you ever been accused of thinking with your stomach? Well, as it turns out, this saying isn’t as far-fetched as it sounds.

As we’ve learned, our gut has its own nervous system that allows it to work on its own, instinctually. This is called the enteric nervous system, or intrinsic nervous system, and it’s made up of around 500 million neurons. And compared to the rest of the organs in our body, the variety of neurons that make up this system is only surpassed by the brain itself.

As well as having its own nervous system, the gut also accounts for 80 percent of our immune system. Considering that most of the dangerous bacteria and pathogenic germs enter our body through our mouth, however, this fact might not come as a surprise.

But not all of the bacteria our bodies are exposed to is dangerous. In fact, our health is dependent upon the work of microorganisms.

Yes, it would seem that even after three million years of evolution, we are still learning about the importance of the many microorganisms in our gut. There are as many as 100 trillion microorganisms in our digestive tract, a community called the gut flora. And they may have an intimate relationship with our brain.

Consider this question: Is it possible that microbes in our gut tell our brain what kind of food we’re craving?

The example of Toxoplasma gondii shows that some microorganisms taking up residence in our gut are bad news. But we certainly shouldn’t write off all microbes – after all, we spend our entire lives with them, no matter how much disinfectant we use!

Our attitude toward microbes has evolved over time; at the turn of the twentieth century, for instance, there were two opposing views.

Well, we’ve reached the last stop on our journey through the gut: the large intestine, also known as the colon.

As your food enters the large intestine, the digestion process has been finished. Any remaining water is reabsorbed and the feces is prepared for defecation. At the end of this process, the food waste reaches the rectum, which is where our sphincter muscles reside.