Someone Crack a Window!

Happy Tuesday, friends! Today’s post is one of my best friend’s favorite facts and will be one of yours too if you enjoy a second graders humor. It is also something you will always remember and think about…


Why is your colon shaped the way it is?
As always, let’s start with the basics…

The human colon is a key part of the digestive tract and is present to remove excess water and salts from your solid waste. There are four portions of the human colon (the ascending colon, the transverse colon, the descending colon and the sigmoid colon) and when you take those four sections and add the rectum and cecum, you get the large intestine. The large intestine is a little shy of 2 meters long. Chyme (contents of digestion) comes into the colon already striped of the vast majority of its nutrients and water. As muscle contractions (peristalsis) move the chyme along, it comes in contact with your body’s lovely supply of gut bacteria that help turn the chyme into feces (that’s the scientific word for poop – just in case you didn’t know). The feces will move into the rectum, which will fill and stretch until nerve endings on the internal recto-anal sphincter tell the body it’s time to hit up a bathroom. A sphincter if like a valve – it can open and close to allow things to move through or not. Your internal sphincter is involuntary (meaning you cannot control it), but thankfully your external recto-anal sphincter is voluntary. As a baby you learn to control this sphincter to regulate when you should get rid of your last meal.

Another byproduct of digestion is gas production. Gas can build up in your body in lots of different ways: forming from the breaking down of food, swallowing air, production by the bacteria in your colon, etc. This gas is known as flatus and is a mixture comprised mostly of nitrogen and oxygen. Just like chyme, flatus is passed through the colon via peristalsis and when it hits that internal sphincter, nerves send messages to the brain that it is time to crack a window. Luckily, just like with feces, flatus can be controlled with the external sphincter.

Basic anatomy and physiology, done - back to the question: why is it shaped the way it is?

If you look at a cross section of your colon (the majority of your large intestine, really), you will see it is not just a hollow tube. It would look more like a scrunchie (with wavy edges that are able to stretch, creating an irregular internal tube appearance) rather than a straw (with smooth internal edges and a constant diameter). This is for a very simple reason.

As peristalsis moves the flatus and feces through your large intestine, it is going to move at different rates and eventually run into each other. The irregular shape and ability to stretch helps allow the gas to move around and past the feces. If it were shaped like a smooth, rigid tube, the gas would build up behind the feces and create lots of pressure. The gas would push the feces through the colon too quickly to be properly processed. That pressure would also be very painful and trying to hold it in would probably be a waste of time. Worst of all, it would also mean every time you passed gas, you would go #2 too. Thanks to evolution, you can release gas and still hold in your #2 until you can get somewhere to get rid of it.

Kind of a gross post, but think about how impressive the body is to figure out that it needs to be designed this way!

And the next time you make a stinky, you are totes going to think about this post.