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by Don Bottoni, RPh, PCCA Clinical Compounding Pharmacist
The gut-brain connection, also known as the gut-brain axis, is one of the most studied systems in our body. This connection consists of a two-way communication between our gastrointestinal (GI) tract (the gut), our brain and trillions of intestinal floral living in our human microbiota.
Our gut and microbiota — collectively known as the enteric nervous system (ENS) — are often referred to as the “second brain.” The ENS lies in the top layers of our intestinal tract and contains more than 100,000 neurons, about the same number of neurons in our spinal cord. The surface area of our intestinal tract is about the size of a tennis court and contains more than 100 trillion organisms that weigh about six pounds.
To say our intestinal tract is a very complex system is an understatement. Our GI tract is more than a food processing machine. The microbiota is not only associated with the assimilation and absorption of nutrients, but also with the health of our immune system and emotional health.
We have all heard of sayings such as “gut feeling,” “butterflies in the stomach,” or “nervous stomach.” These descriptions, in layman’s terms, describe how emotions affect our GI tract. We all have had our stomach “grumble” when it is mealtime or when we see or smell food. Have you ever wondered why we experience diarrhea when we are stressed out? How would we know we are hungry if our brain and gut did not communicate? These are all internal signs of our gut-brain connection activity.
Another gut feeling is a feeling of being full. This feeling is stored in the brain and accessed later for making future food decisions. Ivan Pavlov won a Nobel Prize back in the early 1900s for his work with dogs and their responses to food stimuli. Our ENS communicates with our brain via the vagus nerve (parasympathetic signals sent to the brain), and the peripheral nerves of the spinal cord (the sympathetic signals) sent from the brain to the intestinal tract.
So how do the two organs communicate? The bacterium in the gut produces more than 20 different hormones and many neurotransmitters. Those transmitters include tryptophan, serotonin, gamma-aminobutyric acid (GABA), norepinephrine and many more signaling substances. Over 90% of the serotonin in our body is found in the gut. Certain bacteria have been associated with the production of some of these transmitters. A deficiency of certain bacteria can be associated with schizophrenia. Certain bacteria in the phyla of firmicutes help promote the formation of short-chain fatty acids that aid in reducing inflammation in our gut which, in turn, improves our mood.
Certain bacteria in the gut help produce serotonin in enterochromaffin cells in the lining of the gut. If approximately 90% of the serotonin found in the body is produced in the gut, then one can understand how conditions such as irritable bowel syndrome, depression, cardiovascular disease and osteoporosis are affected by our intestinal health. Having the proper flora in our microbiota is key to healthy living. The serotonin produced in our gut is essential for normal intestinal functions such as the peristaltic contractions that move food through the gut. It is also key to other body functions such as sleep, mood, pain sensitivity and overall well-being.
There are more immune cells living in the lining of our gut than are circulating in our blood or are found in our bone marrow. The food in our gut is the outside world within us. It makes sense that we were created with a special system to protect us from potentially lethal organisms in our food.
Stomach acid is the first line of defense against potentially harmful organisms. The acidic environment of the stomach will kill many pathogens. The next layer of protection is the bile salts. The bile salts also have a germicidal effect on pathogens in our food. The immune cells in the gut are the third layer of protection. We have what is called the gut associated lymphoid tissue (GALT), which is found in organized lymphoid tissue such as Peyer’s patches, and in the mesenteric lymph nodes that are found in the epithelial layer that lines the gut. This system contains activated T-cells, plasma cells, mast cells, dendritic cells and macrophages.
These protective mechanisms come into play when harmful pathogens and material are sensed to be present in the gut. Our epithelial tissue that lines the gut is one cell thick, and it is a protective barrier against microbe penetration.1-8
Visit the PCCA Blog on January 11, 2023, to read Part 2 of The Gut-Brain Connection: Bidirectional Signals for Health & Disease .
A version of this article originally appeared entirely in PCCA’s members-only magazine, the Apothagram.