Anxiety sometimes cause diarrhea, sometimes constipation, and sometimes both. It's interesting because it seems their underlying neurophysiology is somehow different. What are underlying physiological processes that lead to these two symptoms in anxious people? Particularly in terms of the activity of sympathetic and parasympathetic nervous system?
Hraish is right about the relationship between emotions and gut-brain axis. Stress hormones released by the brain are responsible for the gut-brain reflexes. Anxiety is related to stress and stress hormones are released when anxiety is expressed by the individual.
Irritable bowel syndrome(IBS) symptom-based diagnosis, which is having symptoms such as chronic abdominal pain, discomfort, bloating, alteration of bowel habits, diarrhea, constipation etc.
Irritable bowel syndrome (IBS) is a functional digestive disorder characterized by abdominal pain, bloating and altered bowel habits without any organic cause.
(Drossman 1999b; Mulak and Bonaz 2004).
In addition, stress is able to increase visceral sensitivity either at the central and/or peripheral level. (Mulak and Bonaz 2004; Larauche, et al. 2011).
Stress is enabled through the corticotrophin-releasing factor (CRF) system (CRF, urocortins and their receptors CRF1,2), is a key factor involved in the pathophysiology of IBS.
Stress is able to modify visceral sensitivity as well as GI motility, permeability, intestinal microbiota, and immunity of the GI tract, all mechanisms that are involved in the pathophysiology of IBS. In addition, stress is able to modulate the hypothalamic pituitary adrenal (HPA) axis and the autonomic nervous system (ANS) which is the link between the gut and the CNS and an imbalance of the ANS is observed in IBS patients. The main brain areas involved in stress are the prefrontal cortex, the limbic system (e.g. the hippocampus and the amygdala) and the hypothalamus. Relations between the prefrontal cortex and the limbic system are important in the management of stress response. (Pellissier, et al. 2010a; Mazurak, et al. 2012)
One of the most common gut related conditions seen by GPs and Gastroenterologists is Irritable Bowel Syndrome (IBS), previously known as colitis,mucous colitis, spastic colon, and spastic bowel disease.Around 10-20% of adolescents and adults have symptoms consistent with IBS (with females twice as likely as males to report IBS symptoms). IBS is associated with 12 months of abdominal pain or discomfort which is (1) relieved with defecation; and/or (2) associated with change in stool frequency and/ or form (i.e., constipation and/or diarrhoea). IBS is also associated with other gut-related symptoms including: bloating,nausea,and excessive gas. Non-gut related symptoms include fatigue, headaches, sleep problems,and pain conditions, such as fibromyalgia.
Individuals who experience IBS also identify that their gut problems increase doing times of stress.Itcan become a vicious cycle-IBS is exacerbated by stress and stress is inturn increased by symptoms of IBS.With anxiety comes increased muscle tension around the gut (affecting gutmotility) and activation of the flight fight response, reducing blood in the gut (this is what causes butterflies in the tummy!). These physical changes cause the gut-brain to send signals to the brain which in turn promote further stress and distress, most commonly in the form of anxiety.For individuals with IBS (or actually most gut conditions), the ongoing worry about their gut and unproductive patterns can be very debilitating. It can also be the starting point for their anxiety and/or depression. Reference
From the above definitions it is clear that anxiety and brain-gut relationships are valid and IBS is an important reason for gut related disorders when stress is been experienced by the person. Over 10-20 % of adults have symptoms related to IBS, which means a common type of disorder in the general public.