Also in this week's column:
Is it possible to swallow while standing on your head?
Asked by Troy Landis, age 12, of Milwaukee, Wisconsin
Do not try it! Do not even think about trying it! But it is possible to swallow while standing on your head. This is due to the pulling action involved in the swallow itself.
Swallowing is one of those activities we do many times each day and rarely, if ever, think about it. When most people think about swallowing, they probably believe that the food simply falls down the throat (pharynx) due to gravity - rather like rain down the guttering. This is hardly the case. Instead, the food is gradually pulled down the ten-inch passage to the stomach in five to ten seconds.
As a result of this pulling action, it is possible to swallow food or liquid while standing on your head. But it would be very uncomfortable to do so and the danger of choking would be continuous.
Swallowing is a complex act for moving food from the mouth to the stomach. A series of closures to temporarily inhibit respiration occur while constrictive and peristaltic waves move the food and drink (bolus) in rhythmic muscular contractions down the esophagus.
Liquids make the trip in about one second to be drawn into the stomach. Semi-liquids take about five seconds. Solids take about 10 seconds. The whole swallow takes 10 to 12 seconds.
The first phase of swallowing is the termination of chewing the bolus. The bolus is pushed to the back of the throat by the tongue. The tongue does this by pressing against the roof of the mouth (soft palate) forcing the bolus into the throat.
Next, the bolus is pushed down into the esophagus by rhythmical contractions of the esophageal muscles (peristaltic waves). The sphincter muscle at the entrance to the esophagus remains relaxed in order to open the channel of the throat. The larynx must elevate to force the epiglottis to close over the airway (trachea) preventing the bolus from entering the lungs. Peristalic waves continue to push the bolus through the esophagus and down into the stomach. One more muscle sphincter must relax for this to occur and also to prevent the bolus from coming up again.
Stephen Juan, Ph.D. is an anthropologist at the University of Sydney. Email your Odd Body questions to email@example.com