Waarom Moeten We Hikken?

Het langste geregistreerde geval van hikken duurde 68 jaar... en werd veroorzaakt door een vallend varken. Hoewel dit een extreem geval is, hebben we allemaal weleens de hik gehad. Maar wat veroorzaakt de hik in de eerste plaats? John Cameron neemt ons mee naar het middenrif om daarachter te komen.

Charles Osborne began to hiccup in 1922 after a hog fell on top of him. He wasn't cured until 68 years later and is now listed by Guinness as the world record holder for hiccup longevity.

Meanwhile, Florida teen Jennifer Mee may hold the record for the most frequent hiccups, 50 times per minute for more than four weeks in 2007.

So what causes hiccups? Doctors point out that a round of hiccups often follows from stimuli that stretch the stomach, like swallowing air or too rapid eating or drinking. Others associate hiccups with intense emotions or a response to them: laughing, sobbing, anxiety, and excitement.

Let's look at what happens when we hiccup. It begins with an involuntary spasm or sudden contraction of the diaphragm, the large dome-shaped muscle below our lungs that we use to inhale air. This is followed almost immediately by the sudden closure of the vocal chords and the opening between them, which is called the glottis.

The movement of the diaphragm initiates a sudden intake of air, but the closure of the vocal chords stops it from entering the wind pipe and reaching the lungs. It also creates the characteristic sound: "hic."

To date, there is no known function for hiccups. They don't seem to provide any medical or physiological advantage. Why begin to inhale air only to suddenly stop it from actually entering the lungs? Anatomical structures, or physiological mechanisms, with no apparent purpose present challenges to evolutionary biologists. Do such structures serve some hidden function that hasn't yet been discovered? Or are they relics of our evolutionary past, having once served some important purpose only to persist into the present as vestigial remnants?

One idea is that hiccups began many millions of years before the appearance of humans. The lung is thought to have evolved as a structure to allow early fish, many of which lived in warm, stagnant water with little oxygen, to take advantage of the abundant oxygen in the air overhead.

When descendants of these animals later moved onto land, they moved from gill-based ventilation to air-breathing with lungs. That's similar to the much more rapid changes faced by frogs today as they transition from tadpoles with gills to adults with lungs.

This hypothesis suggests that the hiccup is a relic of the ancient transition from water to land. An inhalation that could move water over gills followed by a rapid closure of the glottis preventing water from entering the lungs. That's supported by evidence which suggests that the neural patterning involved in generating a hiccup is almost identical to that responsible for respiration in amphibians.

Another group of scientists believe that the reflex is retained in us today because it actually provides an important advantage. They point out that true hiccups are found only in mammals and that they're not retained in birds, lizards, turtles, or any other exclusively air-breathing animals.

Further, hiccups appear in human babies long before birth and are far more common in infants that adults. Their explanation for this involves the uniquely mammalian activity of nursing.

The ancient hiccup reflex may have been adapted by mammals to help remove air from the stomach as a sort of glorified burp. The sudden expansion of the diaphragm would raise air from the stomach, while a closure of the glottis would prevent milk from entering the lungs.

Sometimes, a bout of hiccups will go on and on, and we try home remedies: sipping continuously from a glass of cold water, holding one's breath, a mouthful of honey or peanut butter, breathing into a paper bag, or being suddenly frightened. Unfortunately, scientists have yet to verify that any one cure works better or more consistently than others. However, we do know one thing that definitely doesn't work.

 

Bron: TED.com