Gastrointestinal Physiology and Function

Abstract

The gastrointestinal (GI) system is responsible for the digestion and absorption of ingested food and liquids. Due to the complexity of the GI tract and the substantial volume of material that could be covered under the scope of GI physiology, this chapter briefly reviews the overall function of the GI tract, and discusses the major factors affecting GI physiology and function, including the intestinal microbiota, chronic stress, inflammation, and aging with a focus on the neural regulation of the GI tract and an emphasis on basic brain-gut interactions that serve to modulate the GI tract. GI diseases refer to diseases of the esophagus, stomach, small intestine, colon, and rectum. The major symptoms of common GI disorders include recurrent abdominal pain and bloating, heartburn, indigestion/dyspepsia, nausea and vomiting, diarrhea, and constipation. GI disorders rank among the most prevalent disorders, with the most common including esophageal and swallowing disorders, gastric and peptic ulcer disease, gastroparesis or delayed gastric emptying, irritable bowel syndrome (IBS), and inflammatory bowel disease (IBD). Many GI disorders are difficult to diagnose and their symptoms are not effectively managed. Thus, basic research is required to drive the development of novel therapeutics which are urgently needed. One approach is to enhance our understanding of gut physiology and pathophysiology especially as it relates to gut-brain communications since they have clinical relevance to a number of GI complaints and represent a therapeutic target for the treatment of conditions including inflammatory diseases of the GI tract such as IBD and functional gut disorders such as IBS.

Inflammation and Gut-Brain Axis During Type 2 Diabetes: Focus on the Crosstalk Between Intestinal Immune Cells and Enteric Nervous System

“…Numerous pathologies that link inflammation, gut microbiota and ENS have been described ( Greenwood-Van Meerveld et al, 2017 ). Along those lines, recent data have shown that specific neurodegenerative diseases (i.e., multiple sclerosis, Parkinson disease) were also characterized by gastrointestinal comorbidities.…”

Epithelial Barrier Function in Gut-Bone Signaling

“…Colonic mucosal biopsies from young and old non-human primates (baboons) demonstrate significant differences in permeability and TJ proteins. The older baboons displayed a significant decrease in ZO-1, occludin, and JAM-A proteins, and an increase in claudin-2 expression, all of which correlated with increased permeability in the old aged group [66]. Another study in monkeys found that old monkeys have an increase in FITC dextran flux compared to young monkeys [67].…”

“…Specifically, the strongest link between gut permeability and bone loss comes from colitis studies where barrier disruption in adult animal models leads to bone loss, even without weight loss [84][85][62]. Thus, as animals and humans age, intestinal permeability increases [64][65][66][67][62][69] and could contributes to age-related bone loss. In addition, increased permeability likely promotes the low-grade chronic inflammation, termed “inflammageing” [72][67][75], and many studies link low grade inflammation with bone loss [84][85][62].…”

In vitro safety evaluation of a povidone‐iodine solution applied to human nasal epithelial cells

“…The permeability of these pathways is typically measured using several complementary methods. TEER measures the net flux of all ions (cations and anions) across the epithelium (pore and leak pathway) 22 . The most common ions in physiological solutions, Na + and Cl − , carry this current.…”