Dear Dru,
When it comes to intestines, it sure seems like two are better than one.
I asked my friend Franck Carbonero why that is. He’s a microbiologist at Washington State University. He studies the bacteria that live inside the human gut.
He told me that the small intestine and the large intestine do different jobs.
Let’s say you sink your teeth into some pizza. You chew it up and swallow it. All those chewed up bits land in your stomach. They mix with digestive juices and start to break down. The broken-down food and digestive juices together are called chyme. After about six hours, your stomach sends that chyme to your small intestine.
The small intestine’s job is to absorb nutrients from the food.
It might be called small, but the small intestine is super long. If you plopped it on the floor and stretched it out, it would be about 20 feet long. That’s about as long as a small school bus.
“The small intestine is so long because it takes quite some time to absorb all the nutrients,” Carbonero said.
It can take six hours for the small intestine to do its job. The nutrients are sucked from the inner surface of the small intestine into the bloodstream. Then they zoom away to other parts of your body. The small intestine sends what’s left to the large intestine.
The large intestine’s job is to absorb any leftover nutrients. Then it recycles extra water from the stew-like chyme. It forms the leftover waste into poop.
The large intestine is wider than the small intestine. But it’s much shorter—about 5 feet long when stretched out. This part of digestion is slower. It can take 3 days.
That’s because digestion in the large intestine involves about 38 trillion helpers. They’re bacteria that live in your large intestine.
“The bacteria evolved to degrade the fiber and leftover food,” Carbonero said. “They ferment it into smaller molecules for their own needs. By doing that, they also release vitamins our bodies can use.”
The kind of digestion bacteria do is called fermentation. That’s when bacteria break down sugars so they can use the energy. In the large intestine, bacteria break down fiber and sugars that we can’t digest on our own. Fermentation also makes vitamins we need.
By splitting up the digestion jobs—and partnering with lots of bacteria—your intestines get everything we can use out of the food we eat. They should really take a bow-el for a job well done.
Sincerely,
Dr. Universe