How does peristalsis let you swallow upside down?

Dear Cecil:

My high school gym teacher used to tell us that peristalsis was so dandy that a human being could swallow water while standing on his head. He was always going to show us, but never did. Tell me if my gym teacher lied--considering what he told us about sex, I have my doubts.

Cecil replies:

Dear E.:

Why the doubts? It’s 100% possible to have sex while standing on your head. It’s also possible to drink while standing on your head, and now that I think about it there’s a very close relationship between having sex while standing on your head and drinking. Whatever your gym teacher had in mind, I’m telling you that’s one classroom demonstration I would not have slept through.

Peristalsis works just like toothpaste, to wit: circular and longitudinal muscles along the walls of the pharynx (throat), esophagus, stomach, and intestines contract in waves, pushing the food or whatever ahead, much like you squeeze that last smidgen of sex appeal out of the tube.

So powerful is the force created by these muscles that food passing through the pharynx is rammed down the line at a speed of about 25 feet per second. Things slow down a tad in the esophagus–here, four to eight inches of muscle contract at a time, and about nine seconds are required for the whole trip from throat to stomach.

Gravity is a secondary consideration, coming into play only when liquids are involved. When you’re sitting up, liquids drop straight through the esophagus, then wait nine seconds or so for the peristaltic contractions to catch up and open the gateway to the stomach. If you’re standing on your head or bending over, peristalsis does the job just fine, as any giraffe will be happy to attest.

Humanity has been sadly shortchanged in the peristalsis department. Cows and other cud-chewing animals (ruminants) have the ability to reverse the direction of peristalsis when necessary, bringing food up from the stomach to the mouth for a few extra chomps. All we have is Barry Manilow.

Send questions to Cecil via cecil@straightdope.com.

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