Abstract
The human gastrointestinal tract harbors most of the microbial cells inhabiting the body, collectively known as the microbiota. These microbes have several implications for the maintenance of structural integrity of the gastrointestinal mucosal barrier, immunomodulation, metabolism of nutrients, and protection against pathogens. Dysfunctions in these mechanisms are linked to a range of conditions in the gastrointestinal tract, including functional gastrointestinal disorders, ranging from irritable bowel syndrome, to functional constipation and functional diarrhea. Irritable bowel syndrome is characterized by chronic abdominal pain with changes in bowel habit in the absence of morphological changes. Despite the high prevalence of irritable bowel syndrome in the global population, the mechanisms responsible for this condition are poorly understood. Although alterations in the gastrointestinal microbiota, low-grade inflammation and immune activation have been implicated in the pathophysiology of functional gastrointestinal disorders, there is inconsistency between studies and a lack of consensus on what the exact role of the microbiota is, and how changes to it relate to these conditions. The complex interplay between host factors, such as microbial dysbiosis, immune activation, impaired epithelial barrier function and motility, and environmental factors, including diet, will be considered in this narrative review of the pathophysiology of functional gastrointestinal disorders.
Highlights
In the human body there are about 39 trillion microbial cells (Sender et al, 2016), the majority of which inhabit the gastrointestinal (GI) tract, forming a dynamic ecological environment collectively known as the microbiota (Schulberg and De Cruz, 2016)
The mechanisms responsible for functional GI disorders (FGIDs) are poorly understood and there is a lack of consensus on what the exact role of the microbiota is, and how changes to it relate to these conditions
FGIDs include functional constipation (FC) and functional diarrhea (FD) where there is a significant change in bowel habit but not abdominal pain, in the absence of alternative pathology
Summary
In the human body there are about 39 trillion microbial cells (Sender et al, 2016), the majority of which inhabit the gastrointestinal (GI) tract, forming a dynamic ecological environment collectively known as the microbiota (Schulberg and De Cruz, 2016). The search was extended by using the references of selected recent articles and systematic reviews or metaanalysis Host factors, such as microbial dysbiosis, low-grade inflammation, altered epithelial barrier function and motility, as well as environmental factors, including diet, will be considered to help shed light on the emerging pathophysiology of FGIDs. IBS is a multifactorial condition characterized by chronic and relapsing abdominal pain and altered bowel habit. FGIDs include functional constipation (FC) and functional diarrhea (FD) where there is a significant change in bowel habit but not abdominal pain, in the absence of alternative pathology These heterogeneous conditions are described as “disorders of gut-brain interaction,” as they can be classified as disorders that span both the GI and the neurological systems (Figure 1). Understanding the etiology and pathophysiology promises an opportunity to develop new, effective and personalized treatments in addition to biomarkers for diagnosis, determining severity and treatment response
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