The Science of Defecation Could Produce Better Medicine for Constipation

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Health and Medicine Science and Technology

The Science of Defecation Could Produce Better Medicine for Constipation






April 27, 2017
• Atlanta, GA








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David Hu is a professor in the George W. Woodruff School of Mechanical Engineering and the School of Biological Sciences.




A new study led by researchers in the George W. Woodruff School of Mechanical Engineering finds that all mammals, from humans to elephants to cats, defecate in the same amount of time: about 12 seconds. That’s despite the fact that the length of their rectums can vary widely. For instance, an elephant’s is 10 times the length of a cat’s (40 centimeters vs. four).

The study suggests that the time is consistent because of mucus. The substance covering the the large intestine is very thin for small animals and much thicker for larger ones. According to the paper, mucus allows feces to move through the intestine “like a sled sliding through a chute.”

The extra fluid allows larger animals to defecate at higher speeds than smaller animals, even though both use the same amount of pressure to relieve themselves. In other words, defecation might not be possible without this previously unknown mucus layer.

The research also found that the length of feces is double that of the rectum, which means the rectum and the colon both store feces.

The study, “Hydrodynamics of defecation,” is published in the journal Soft Matter. It covers a topic that hasn’t been heavily researched within the scientific community. Professor David Hu (also in the School of Biological Sciences) and his mechanical engineering student Patricia Yang are the lead authors. Daniel Chu, an assistant professor and colorectal surgeon at the University of Alabama at Birmingham, is one of the co-authors. Georgia Tech spoke with each of them about their findings.

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