The gut has a nervous system of its own called the “enteric nervous system”. It has about as many neurons as the spinal cord and is metaphorically called “the brain of the gut”.
The gut has developed powerful mechanisms to defend the body against invading antigens derived from food, bacteria, parasites, toxins and other compounds. Its outer cell lining, the epithelium, constitutes the inner surface of the body that is highly permeable in most parts of the gut, in particular the small intestine. When the gut lining is damaged through stress, medication or poor diet (namely inflammatory allergens like gluten), gap junctions in the lining allow toxins to pass through and be picked up by immune cells. The immune cells then launch an inflammatory response which is where “irritable bowel syndrome” stems from.
The gut contains the largest immune system of the body, collectively called “gut-associated lymphoid tissue” (GALT) that continuously surveys antigens passing through the gut. The GALT works hand-in-hand with enteric nervous system, the gut endocrine (hormone) system as well as the spine to set up a powerful local defence system. The brain is advised about the actions of this defence system by activity in the spinal cord.
The brain modulates the functions of the enteric nervous system via the spinal cord. It receives detailed information from the gut by appropriate impulse activity in the spinal cord as well as gastrointestinal hormones. As the brain adapts to stress and the environment, so too does the behaviour of the gut. When the gut becomes more damaged and permeable to toxins, the brain changes, and its top-down emotional and cognitive control is disturbed through “efferent” pathways. One becomes more sensitised to pain, and stress and anxiety have a negative impact on the function of the gut’s immune system.
The immune system of the intestine is involved in every process of the gastrointestinal tract that potentially leads to its damage, e.g. inflammation, injury, allergies, infections. In the video below, an immune response is illustrated when the gut lining is damaged. M-cells of the intestinal lining transport antigens to macrophages and dendritic cells, the first line of the innate natural defence system. The antigens are then presented to T cells, the second line of defence, which stimulate B cells. The B cells proliferate in the gut and produce antibodies. They then enter general circulation and localise to the lymphoid tissue in the intestine. When this process becomes uncontrolled, chronic inflammation occurs.
Chronic inflammation will lead to further intolerance to allergens such as gluten and continue to damage the brain through “afferent” pathways, making one more prone to anxiety, depression and lower pain thresholds overall, particularly in the spine.
© Dr Neil Bossenger 2013
