Gershon, Michael
<p class="default">07:06 PM, October 15, 2007
 
Michael Gershon ... the second brain gets a lot of press from Brenda Watson.
 
The Enteric Nervous System has 100 million neurons. It contains 95% of the serotonin of the body.
See espec. page 2:
 
But it turns out that irritable bowel syndrome, like depression, is at least in part a function of changes in the serotonin system. In this case, it is  <b>too much serotonin</b> rather than too little.
In a healthy person, after serotonin is released into the gut and initiates an intestinal reflex, it is whisked out of the bowel by a molecule known as the serotonin transporter, or SERT, found in the cells that line the gut wall.
People with irritable bowel syndrome do not have enough SERT, so they wind up with  <b>too much serotonin floating around, causing diarrhea</b> .
 
Another mechanism that lends credence to physiology as the source of intestinal dysfunctions is the system  <b>of mast cells in the gut</b> that have an important role in immune response.
"During stress, trauma or 'fight or flight' reactions, the barrier between the lumen, the interior of the gut where food is digested, and the rest of the bowel could be broken, and bad stuff could get across," Dr. Wood said. "So the  <b> big brain calls in more immune surveillance at the gut wall by activating mast cells</b> ."
 <b>These mast cells release histamines and other inflammatory agents, mobilizing the enteric nervous system to expel the perceived intruders, and causing diarrhea</b> .
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