biology zoology blog swallowing in reverse

Swallowing in Reverse

What was swallowing in reverse called again?

During the time I was working for a TV’s education channel, I had plans for a series on food and nutrition. The opening sequence was meant to show a family sitting around the dinner table and helping themselves to some food, perhaps a bit of fish, potatoes, cauliflower etc. and just after having put some food in the mouth, I wanted the film to reverse and the food to come out again and end up on the plate as before. And then I wanted the film to show the sign ‘STOP’, and a voice saying “Let’s find out more about this food”. Unfortunately, the producer didn’t like my idea and my series (at least not with my idea) never got off the ground.

You may wonder how I got that idea of reversing the introductory sequence in my film on food and, eating and digestion. Well, in a movie anything backwards looks quite funny, but in real life, it often isn’t funny at all. Someone, for instance, who watches his pregnant wife endure daily attacks of nausea and morning sickness may wonder why there is no religion that requires men to utter daily prayers of thanks that they aren’t women! As unpleasant as vomiting (and even the words describing the action, e.g. spewing up, throwing up) may be, from a physiological viewpoint -and only then- vomiting is actually a very interesting phenomenon. It obviously exists to safeguard the body from something ingested, which could possibly do some harm to the body and has to be got rid off.

The act of swallowing-in-reverse is under the control of a centre in the medulla of the brain and in ruminant animals like cows, sheep, deer etc. the process has been perfected into the essentially life-sustaining art of “swallowing their cud”. In other animals, and the human being, stimulation of the vomiting centre can be a bump on the head, chemicals released from the ingested food, meningitis, encephalitis, a brain tumour or hormones. The increase of chorionic gonadotropins during pregnancy in combination with changes of the carbohydrate metabolism triggers the morning sickness and the sudden rise from a reclining to an upright position does not help either. As a protective behavioural reflex, vomiting can be induced by chemical irritants in the duodenum and the stomach or by mechanical stimulation of the back of the throat (as bulimia and anorexia sufferers know very well).

To expel and eject the stomach content, the stomach needs to be relaxed while the abdominal musculature contracts rhythmically and forcefully. During the act of vomiting, respiration is impossible and the glottis is closed so that stomach contents do not block the nose or enter the trachea. All this happens automatically and requires no thinking or learning. Regurgitation, crop-emptying, and the bringing-up of food are also widespread phenomena in parental birds and mammals to supply their young with nourishment, but it can also serve as part of a defence reaction aimed at spoiling the appetite of a might-be predator. In some insects, the regurgitated material is sticky and smelly and effectively turns off an attacker’s desire to continue its attack. But let’s end with something sweet. Honey, by the way, owes its thick and sugary taste to the repeated regurgitation and re-swallowing of the ingested nectar material by numerous bees. But when you savour this delicious, healthy and tasty syrupy food, you need not have to think of the many stomachs it has been in before it entered your mouth. Bon appétit!

© Dr V.B. Meyer-Rochow and, 2018.
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