Functional GI disorders are common in the general population, with a reported prevalence of 25-40%. Functional GI disorders are responsible for up to 40% of office consultations to gastroenterologists (Talley, 1994; Drossman, 2006). The burden of IBS is estimated to be $1.6-$10 billion in direct costs and $19.2 billion in indirect costs in US.
Irritable bowel syndrome (IBS) and functional dyspepsia (FD) have no known organic cause. The motor dysfunction of GI tract and visceral hypersensitivity are considered especially important factors for IBS and FD etiology (Drossman, 2006; Van Oudenhove et al., 2010). Disorders of colonic motility may contribute to symptoms in constipation- or diarrhea- predominant IBS (Vassallo et al., 1992; Camilleri et al., 1999).
Pathogenesis of FD and IBS is highly associated with stress. GI symptoms may depend on the degree of strength, duration and accumulation of various types of mental and social stress. In addition, these disorders could also depend on how we adapt to the stressful events in our daily life.
Epidemiological studies suggest considerable overlap between FD and IBS. About half of the FD patients fulfill the criteria for IBS (Corsetti et al., 2004). The possible explanation of the overlap is that the dysfunction of upper and lower gut are due to the expression abnormality of OXT and CRF at the hypothalamus.