Let's turn inside today and consider the fact that our stomachs "growl."
Dr. Michael Picco, a gastroenterologist at the Mayo Clinic, explains that stomach growling can typically be chalked up to normal digestion. It does not occur only when we are hungry, but also after eating or between meals when food is passing through our intestines. Appetite is controlled by the release of hormone-like substances which cause the brain's hypothalamus to stimulate our desire to eat. A message sent to our stomach and intestines triggers muscle contractions and the release of digestive fluid, which produce the noise as we prepare to eat. The response is triggered by hunger - but can also be stimulated by the thought, sight, or smell of food. Only if stomach noise is excessive and accompanied by bloating, cramping, diarrhea, or excess gas, is it a possible sign of an underlying disorder.
Physiologist Mark A.W. Andrews of the Lake Erie College of Osteopathic Medicine says that the reason stomach growling is associated more with hunger than digestion is that it is typically louder when the stomach and intestines are empty and their contents don't muffle the noise. The science behind the noise itself is that the walls of the gastrointestinal tract - a hollow tube that runs from mouth to anus - are layered with smooth muscle. When activated, they squeeze the tract's contents to mix and propel food, gas, and fluids through the system, generating the rumbling. The squeezing (peristalsis) involves a ring of contraction that moves down the tract a few inches at a time. Though the rate and force of peristalsis typically increases in the presence of food, he explains, activity also increases after the stomach and small intestines have been empty for approximately 2 hours. They may continue for 10 to 20 minutes once initiated, and then repeat every 1-2 hours until the next meal is ingested.
The word that the ancient Greeks came up with for the growling of the stomach was an attempt to put the sound into words and is the origin for the medical term:
bor·bo·ryg·musSeveral bodily noises in English - belch, growl, gurgle, hiccup, rumble, slurp, snort - are also onomatopeiac.
n. pl. bor·bo·ryg·mi (-mī')
A rumbling noise produced by the movement of gas through the intestines.
[New Latin, from Greek borborugmos, of imitative origin.]
I've illustrated this post with a photograph of the giant colon (1st image) on display at Philadelphia's Mütter Museum. The colon belonged to a sideshow performer who was billed as the "Balloon Man" and the "Human Windbag" because his severe constipation distended his belly and gave it an unusual shape that people would pay to see. He died at age 29 in 1892, and an autopsy revealed that he had accumulated 40lbs of feces. His colon - now stuffed with paper, as I recall - measures 8' in length and 27" in circumference. The x-ray (2nd image) shows the megacolon of a living 55-year-old patient, which measures approximately 10cm in maximum diameter. The arrows point to pseudopolyps and the condition required emergency surgery.