It has probably never occurred to you that your ever-so-ordinary bowel movement may entail mysterious, previously unknown actions. Although they've understood the bigger picture for some time now, scientists have long been mystified by the nitty gritty of this most routine of bodily processes. Now, Canadian gastroenterology scientists working with colleagues in China have discovered how interacting motions work together to create a specific rhythm, which results in elimination. "It's like when a stone is dropped in water, it creates waves or motion that pushes things along, but when a second stone is dropped in the water, the movement changes to up and down, appearing to stay in the same place," Dr. Jan Huizinga, a professor of medicine at McMaster University, commented in a press release.

Inner Dynamics

For those who eat, there must also be a system of removal to rid the body of what remains after the digestive system — the stomach, small intestine, and colon — has done its important job of absorbing all the nutrients from food. A bowel movement, then, is simply the way in which your body discards waste. Specifically, it does this by compacting the remainders of food into a mass referred to as stool or feces, and then passing this mass through the rectum and anus. Unpleasant (or comical) though this may seem, your bowel movement is an indicator of your general health. A variety of different patterns and routines all suggest well-being. Some healthy people, for instance, have only three bowel movements per week, while others have three every day. Patterns and frequency may change, but if everything else remains the same, this is most likely not a sign of illness. On the other hand, if you begin to experience pain, see blood, or repeatedly pass narrow, ribbon-like stools or loose, watery stools, it’s no laughing matter: time to see a doctor.

Now, it’s long been known how food moves through the gastrointestinal tract. The hollow organs contain a layer of muscle within their walls that enables movement, which is called peristalsis. This movement not only mixes food and liquid together but propels the combination through the digestive tract. The muscles contract and relax, with peristalsis appearing like an ocean wave as food journeys to its end. Scientists have also identified another type of movement, referred to as segmentation contractions, which mainly occur in the large and small intestines.

Studying the two types of movement, Huizinga, working with a team of researchers from the Farncombe Family Digestive Health Institute at McMaster University, the University of Toronto, and Wuhan University in China, noted that unlike peristalsis, which primarily forces food through the tract, segmentation contractions appeared to be responsible for absorption. Perhaps for this reason, these movements worked in a very different matter and though experimentation, the team of scientists overturned all previous hypotheses explaining how exactly it works. "The dominant theory suggests alternate excitation and inhibition from the enteric nervous system," the authors wrote in their published article. "Here we demonstrate that typical segmentation can occur after total nerve blockade." Essentially, the researchers discovered that the motion known as segmentation contractions only occurs when two sets of pacemakers interact to create a specific rhythm. Working together with nerves and muscle, the interaction generates movement that allows for nutrient absorption.

As doctors well know, in cases of diarrhea, segmentation activity is too low, while in cases of constipation, it is too high. In fact, most pain related to eating is caused by abnormal contractions. This new discovery, then, will provide direction to researchers attempting to identify nutrients or develop drugs, which can combat disorders causing malabsorption, diarrhea, constipation, or bloating.

 

Source: Huizinga JD, Chen J-H, Zhu YF, et al. The origin of segmentation motor activity in the intestines.  Nature Communications. 2014.