The GI tract plays a major role in digestion, the immune system, and the production of hormones and neurotransmitters. It processes food and absorbs nutrients and water, while excreting and keeping out unwanted toxins. The lining of the intestines acts as a barrier that allows fully digested foods to pass through its lining and enter the bloodstream. The cells that line the intestines act as a filter between the environment and the body. Without the GI tract barrier, our bodies would reject all food that we ingest. The body sees food as a foreign substance. Foreign substances that produce an inflammatory immune response are known as antigens. The role of the GI tract is to keep out all antigens that are detrimental to the body. Antigens include food, bacteria, and toxins (anything that is foreign to the body).
Here is an example of how the GI tract protects us. Animal protein is a good source of protein for muscles. A doctor should theoretically be able to inject animal protein directly into your biceps to build muscle. This would assure that the protein goes directly to your muscles.
However, if a doctor did this, within hours your body would be overwhelmed by the injection of this foreign substance. Inflammation and infection would spread throughout the bloodstream to all parts of the body. It would lead to inflammation and sepsis (total body infection). If the protein is not removed and the infection and inflammation are not treated soon enough, death would quickly ensue. The GI tract however, allows us to take in foreign substances such as animal protein on a daily basis without any inflammatory response. Therefore, the protective role of the GI barrier is critical in that it allows us to ingest the foods that we need without potential deadly consequences.
Unfortunately, under stress this protective mechanism and other functions of the GI tract are disrupted. The GI tract contains the largest part of the body’s immune system in its mucosal (inner) lining. The GI immune systems role is to ensure that unwanted entities don’t cross the GI tract and enter the blood. The gastrointestinal tract is the first line of defense against pathogens, which enter the body through food we ingest. However, under stress, unwanted pathogens (bacteria and viruses that can cause disease), toxins, and food substances are not destroyed by the immune system and are allowed to cross the barrier, leading to infection and inflammation throughout the body.
To make matters worse, stress decreases saliva production and digestive enzymes; therefore, food is not completely digested. Undigested foods irritate and damage the intestinal lining, making them more permeable. The intestinal mucosal cell junctions loosen and allow unwanted matter in the intestines to pass through into the blood. These unwanted substances trigger the immune system and lead to an inflammatory reaction.
Consequently, food allergies are likely to develop during times of stress due to the undigested food entering the blood and causing an inflammatory reaction. This inflammatory reaction can lead to inflammatory and, in some cases, autoimmune diseases. Individuals diagnosed with food sensitivities and inflammatory and autoimmune diseases should be evaluated for GI dysfunction.
In addition, digestive acid production decreases while gastric (stomach) emptying into the intestines diminishes. Harmful bacteria that reside in the intestines and normally controlled by gastric acid are now able to flourish. An antibody known as secretory SIgA is contained in intestinal mucus and destroys many of these microorganisms. But SIgA is decreased by stress which contributes to further pathogen overgrowth. Large intestinal motility increases under stress, which hinders the primary role of the colon the absorption of nutrients and water.
Figure 27 below illustrates the adverse effects of stress on the GI tract.
The Stomach The Other Brain
If you have ever felt butterflies in your stomach just before giving a big presentation or found yourself running to the bathroom the night before a big exam, you probably already know that stress can wreak havoc on your digestive system. The gut is full of nerves or neurons, which may explain why we feel stress in our gut. Sometimes it seems that our gut knows we are stressed before we do. However, how is this possible?
The brain is often seen as the command center of the body, telling every organ what to do and when to do it. However, the gastrointestinal (GI) tract, which includes the esophagus, stomach, and small and large intestines, also has a mind of its own called the enteric nervous system (ENS). The ENS is located in the mucosal tissue that lines the GI tract. The ENS functions independently of the brain. It contains more neurons than the brain. The GI tract produces far more serotonin than the brain and is responsible for over 90% of all serotonin produced by the body. It also produces other neurotransmitters, e.g. dopamine, acetylcholine, norepinephrine, and endorphin. Therefore, it is important to address GI health when treating depression, anxiety and other psychological conditions.
The presence of a nervous system in the GI tract does not mean that the brain does not communicate with the GI tract. In fact, it is actually the opposite. The nerves of the ENS provide a direct link from the stomach to the brain and vice versa, opening up a channel for two-way communication. The ENS is made up of the same type of cells that compose the brain. It produces and uses many of the same hormones and neurotransmitters. The brain and the ENS essentially speak the same language.
Information is constantly being relayed to the brain from the gut via these relatively well-defined pathways, which travels through the vagus nerve. When you are sick, these signals may be responsible for the sensation of nausea. Unpleasant events in the gut can also be perceived by the brain as painful because of information conveyed by the spinal nerves and other nerves leading up to the brain.
During times of stress, these pathways are activated to cause more harm than good. The normal movement of the upper GI tract is suppressed, causing a delay in stomach emptying, thereby keeping food in the stomach longer than normal. At the same time, the colon becomes more active and empties to decrease any excess baggage so that the body is more lightweight. In humans, this combination causes a lack of appetite and an overwhelming urge to empty your bowels.
Studies have shown that stressful events have been linked to the development or worsening of symptoms of most chronic disorders of the digestive system, including:
- Functional Gastrointestinal Disorders (FGD), also known as Leaky Gut Syndrome
- Irritable Bowel Syndrome (IBS)
- Gastro-esophageal Reflux Disease (GERD), also known as acid reflux
- Peptic Ulcer Disease
Points to Remember
- The gastrointestinal tract is important for digestion, immunity and balance.
- Stress has adverse effects on the GI tract, which leads to GI dysfunction and disease.
- GI dysfunction can lead to inflammatory and autoimmune diseases.
Reference: The Stress Connection, Drs. Eldred and Ava Taylor. (Copyrighted 2014.)
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