MEDICAL MATTERS:The workings of the body can still surprise, writes MUIRIS HOUSTON
WHEN WE think of our organs we associate each with a particular function: our hearts pump blood around the body; our intestines process the food we have eaten, extracting nutrients and producing faecal matter; and our lungs take in oxygen and get rid of carbon dioxide.
Recently, however, two events have got me thinking about this traditional view of the body’s anatomy and functions. One was a television programme broadcast by the BBC last week; the other a fascinating talk at the Tedmed event in Washington in April.
Michael Mosley has narrated some top-notch programmes on health issues in the past year or so. A medic, he wears his heart on his sleeve and presents with an endearing boyishness that belies his middle age.
In his latest offering, Guts: The Strange and Mysterious World of the Human Stomach, he swallowed a “pill camera”, allowing us to follow the passage of his morning porridge through his gastrointestinal system.
“Its first stop was my stomach, whose complex work is under the control of what’s sometimes called ‘the little brain’, a network of neurons that line your stomach and your gut. Surprisingly, there are over 100 million of these cells in your gut, as many as there are in the head of a cat,” he said.
All these nerve cells lining our digestive system keep in close touch with the brain via the vagus nerve. According to Mosley, “when we experience ‘butterflies in the stomach’, this really is the brain in the stomach talking to the brain in your head. As we get nervous or fearful, blood gets diverted from our gut to our muscles and this is the stomach’s way of protesting.”
This new appreciation of the “stomach as brain” has influenced how surgeons approach gastric bypass operations. It’s no longer a case of simply reducing the size of the obese patient’s stomach to ensure less food consumption.
Instead, the shrunken stomach is attached further down the small intestine to a section called the ileum. This part of the intestine secretes a gut hormone called PYY, which transmits an “I’m full” message to the brain.
Because the ileum has been attached closer to the stomach than normal, the brain gets the message a lot quicker than it would in those of us who haven’t had a gastric bypass.
At Tedmed, Dr Jonathan Eisen of the University of California got our attention when he mentioned faecal transplants.
This arose from his talk about the “microbial cloud” that lives both on and in each of us. It too works a little like a functional “organ”. He detailed the studies that show how our microbial residents help develop our immune system and influence our metabolic rate.
Eisen is a pioneer in the use of high-throughput computational methods to study microbes by analysing their genomes, but this didn’t prevent him from giving a highly accessible 15-minute talk to an audience whose familiarity with genome analysis may not have withstood much scrutiny.
He told a story of how surgeons who carried out ileal transplants – yes, that same part of the intestine featured in Mosley’s programme – reflexly sterilised the donor ilea before transplantation in the recipient. However, the patients ran into problems linked to the absence of the normal gut flora in the transplanted intestines.
In response, one surgical team decided to leave some of the donor’s microbes within the ileum they were about to transplant. The recipient recovered normal gut function much quicker than those given the super-sterilized ilea.
This outcome has prompted other researchers to experiment with faecal transplants. However distasteful the thought of delivering faecal matter per rectum to a recipient might be, the bottom line (sorry) is that a community of microbes delivered in this way has helped those struck down with the antibiotic-resistant bug clostridium difficile.
So we have a stomach with brains and a cloud of microbes acting as a functional organ. It’s almost enough to make a faecal transplant desirable.