There is a significant connection between mental well-being and gastrointestinal issues. Many people with irritable bowel syndrome (IBS) report that stress and anxiety can cause an increase in their symptoms. Certain situations, feelings, or thoughts can worsen abdominal pain, bloating, constipation, or diarrhea. In order to better manage IBS symptoms, one must understand how the gut and the brain are related.
What is the “gut-brain connection”?
“Gut-brain,” “second brain,” and “little brain” all refer to the enteric nervous system (ENS). It includes more than 500 million nerve cells and is part of the autonomic nervous system (ANS).
We often talk about a “gut feeling” during decision-making or mood perception. Our gut feelings can also provide insight into whether we feel stress or anxiety, which majorly influence the gut-brain. The abdomen can detect stress and anxiety in the body and report back to the brain. Conversely, the gut can also affect our mood and create additional stress. This bidirectional relationship
—called the gut-brain axis
—occurs via nerves, hormones, special messengers, and the microbiome.
If disorders occur with the gut-brain, the mobility of the intestine (motility) may be disturbed. Today, it is believed that dysmotility—impaired function of the muscles of the intestinal wall—is one important cause of IBS.
How does the gut-brain interact with the rest of the autonomic nervous system?
Because the gut-brain works independently from the brain, we can only control our digestive system's activity involuntarily. The gut-brain controls this activity through constant communication with the autonomic nervous system (ANS) in the rest of the body.
The ANS consists of three branches that should work together harmoniously:
- The enteric nervous system (ENS) or “gut-brain” (described above)
- The parasympathetic nervous system (PSNS)
- The sympathetic nervous system (SNS)
Both the PSNS and the SNS directly affect digestive function, ENS communication, and modify its activity. Chemical substances called neurotransmitters bind to receptors in organs and have effects on them.
How does the parasympathetic nervous system (PSNS) affect the gut?
The parasympathetic nervous system (PSNS) is responsible for the processes that help us feel relaxed and calm. The PSNS activates when our brain tells us that we are not under pressure or in imminent danger.
The PSNS is very important for the body’s regenerative processes. It promotes digestion and the synthesis of glycogen, the storage form of sugar (glucose) in the body cells.
The parasympathetic nervous system is also involved in the:
- Absorption of food
- Dilatation of blood vessels leading to the digestive system, resulting in increased blood flow
- Increased contraction of muscle cells in the digestive organ walls, resulting in increased gut motility
- Increased secretion of substances promoting digestion
- Relaxation of muscle cells of sphincters, the muscles in passages or openings of the body
How does the sympathetic nervous system (SNS) affect the gut?
In reaction to an imminent physical or psychological danger, the sympathetic nervous system (SNS) activates the entire body with the “fight-or-flight response.”
The body releases the stress hormones adrenaline and cortisol, and the liver provides our muscles with blood sugar for energy. The blood vessels of organs unnecessary for immediate survival—i.e. skin or the digestive tract—narrow and result in increased blood flow to muscles.
The SNS causes an increase in heart rate, blood pressure, breathing, and muscle tension; sometimes, it also causes bladder contraction.
In the gut, the SNS inhibits digestion through:
- Constriction of blood vessels in the gastrointestinal tract
- Decreased gut motility
- Decreased contraction of smooth digestive muscles
- Contraction of muscle cells of sphincters
How does the autonomic nervous system related to irritable bowel syndrome (IBS)?
Stress and anxiety, among other factors, are known to exacerbate IBS symptoms via nervous system dysregulation. Even though stressful situations often do not demand a physical response, the SNS activates the “flight or fight” response to give the body energy, which is then not fully used.
This excess energy may be a reason why chronically stressed people suffer from physical symptoms, such as:
- muscle tension
- neck pain
- increased heart rate
- gastrointestinal problems
People with IBS may be more easily anxious and stressed by external stimuli than others. During rest periods, this typically subsides.
The accumulation of stress over time can ultimately lead to nervous system dysregulation, or the imbalance between the nervous system's activating and calming mechanisms. Normal communication between various parts of the nervous system is disrupted, and digestion reacts more strongly to external influence and stress than it normally would. Stress is known to aggravate irritable bowel symptoms.
How can stress and anxiety aggravate irritable bowel symptoms? How can one mitigate this?
It is hardly surprising that stress is closely related to the severity of IBS symptoms. Stress and intestinal problems strongly influence each other.
With IBS, microinflammation in the intestinal wall can occur, which causes altered gut motility and increased intestinal sensitivity. As a result, irritable bowel symptoms may be perceived as more intense, which can further increase one's stress levels. This can result in a vicious cycle, as the additional stress may exacerbate symptoms even further.
Stress also disturbs gut flora, because the microbiome is involved in the stress response. Because healthy gut flora increases one's resilience to cope with stress, it can help to reduce stress in the context of irritable bowel treatment, for example, through physical activity or relaxation techniques.
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