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The microcirculation of the gastrointestinal tract is under the control of both myogenic and metabolic regulatory systems. The myogenic mechanism contributes to basal vascular tone and the regulation of transmural pressure, while the metabolic mechanism is responsible for maintaining an appropriate balance between O2 demand and O2 delivery. In the postprandial state, hydrolytic products of food digestion elicit a hyperemia, which serves to meet the increased O2 demand of nutrient assimilation. Metabolically linked factors (e.g., tissue pO2, adenosine) are primarily responsible for this functional hyperemia. The fenestrated capillaries of the gastrointestinal mucosa are relatively permeable to small hydrolytic products of food digestion (e.g., glucose), yet restrict the transcapillary movement of larger molecules (e.g., albumin). This allows for the absorption of hydrolytic products of food digestion without compromising the oncotic pressure gradient governing transcapillary fluid movement and edema formation. The gastrointestinal microcirculation is also an important component of the mucosal defense system whose function is to prevent (and rapidly repair) inadvertent epithelial injury by potentially noxious constituents of chyme. Two pathological conditions in which the gastrointestinal circulation plays an important role are ischemia/reperfusion and chronic portal hypertension. Ischemia/reperfusion results in mucosal edema and disruption of the epithelium due, in part, to an inflammatory response (e.g., increase in capillary permeability to macromolecules and neutrophil infiltration). Chronic portal hypertension results in an increase in gastrointestinal blood flow due to an imbalance in vasodilator and vasoconstrictor influences on the microcirculation. Table of Contents: Introduction / Anatomy / Regulation of Vascular Tone and Oxygenation / Extrinsic Vasoregulation: Neural and Humoral / Postprandial Hyperemia / Transcapillary Solute Exchange / Transcapillary Fluid Exchange / Interaction of Capillary and Interstitial Forces / Gastrointestinal Circulation and Mucosal Defense / Gastrointestinal Circulation and Mucosal Pathology I: Ischemia/Reperfusion / Gastrointestinal Circulation and Mucosal Pathology II: Chronic Portal Hypertension / Summary and Conclusions / References / Author Biography
Three distinct types of contractions perform colonic motility functions. Rhythmic phasic contractions (RPCs) cause slow net distal propulsion with extensive mixing/turning over. Infrequently occurring giant migrating contractions (GMCs) produce mass movements. Tonic contractions aid RPCs in their motor function. The spatiotemporal patterns of these contractions differ markedly. The amplitude and distance of propagation of a GMC are several-fold larger than those of an RPC. The enteric neurons and smooth muscle cells are the core regulators of all three types of contractions. The regulation of contractions by these mechanisms is modifiable by extrinsic factors: CNS, autonomic neurons, hormones, inflammatory mediators, and stress mediators. Only the GMCs produce descending inhibition, which accommodates the large bolus being propelled without increasing muscle tone. The strong compression of the colon wall generates afferent signals that are below nociceptive threshold in healthy subjects. However, these signals become nociceptive; if the amplitudes of GMCs increase, afferent nerves become hypersensitive, or descending inhibition is impaired. The GMCs also provide the force for rapid propulsion of feces and descending inhibition to relax the internal anal sphincter during defecation. The dysregulation of GMCs is a major factor in colonic motility disorders: irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), and diverticular disease (DD). Frequent mass movements by GMCs cause diarrhea in diarrhea predominant IBS, IBD, and DD, while a decrease in the frequency of GMCs causes constipation. The GMCs generate the afferent signals for intermittent short-lived episodes of abdominal cramping in these disorders. Epigenetic dysregulation due to adverse events in early life is one of the major factors in generating the symptoms of IBS in adulthood.
The mammalian gastrointestinal mucosa is a rapidly self-renewing tissue in the body, and its homeostasis is preserved through the strict regulation of epithelial cell proliferation, growth arrest, and apoptosis. The control of the growth of gastrointestinal mucosa is unique and, compared with most other tissue in the body, complex. Mucosal growth is regulated by the same hormones that alter metabolism in other tissues, but the gastrointestinal mucosa also responds to host events triggered by the ingestion and presence of food within the digestive tract. These gut hormones and peptides regulate the growth of the exocrine pancreas, gallbladder epithelium, and the mucosa of the oxyntic gland region of the stomach and the small and large intestines. Luminal factors, including nutrients or other dietary factors, secretions, and microbes that occur within the lumen and distribute over a proximal-to-distal gradient, are also crucial for maintenance of normal gut mucosal regeneration and could explain the villous-height-crypt-depth gradient and variety of adaptation, since these factors are diluted, absorbed, and destroyed as they pass down the digestive tract. Recently, intestinal stem cells, cellular polyamines, and noncoding RNAs are shown to play an important role in the regulation of gastrointestinal mucosal growth under physiological and various pathological conditions. In this book, we highlight key issues and factors that control gastrointestinal mucosal growth and homeostasis, with special emphasis on the mechanisms through which epithelial renewal and apoptosis are regulated at the cellular and molecular levels.
On July 9-10, 2014, the Institute of Medicine's Food Forum hosted a public workshop to explore emerging and rapidly developing research on relationships among the brain, the digestive system, and eating behavior. Drawing on expertise from the fields of nutrition and food science, animal and human physiology and behavior, and psychology and psychiatry as well as related fields, the purpose of the workshop was to (1) review current knowledge on the relationship between the brain and eating behavior, explore the interaction between the brain and the digestive system, and consider what is known about the brain's role in eating patterns and consumer choice; (2) evaluate current methods used to determine the impact of food on brain activity and eating behavior; and (3) identify gaps in knowledge and articulate a theoretical framework for future research. Relationships among the Brain, the Digestive System, and Eating Behavior summarizes the presentations and discussion of the workshop.
AN INSTANT NEW YORK TIMES BESTSELLER AS SEEN ON NETFLIX’S HACK YOUR HEALTH: THE SECRETS OF YOUR GUT “Everything you ever wanted to know about the gut (and then some).” —SELF Discover the secrets of your digestive system—and how to hone a healthy gut—plus new research on the mind-gut connection. With quirky charm, science star and medical doctor Giulia Enders explains the gut’s magic, answering questions like: What’s really up with gluten and lactose intolerance? How does the gut affect obesity? What's the connection between our microbiome and mental health? Why does acid reflux happen? In this revised edition of her beloved bestseller, Enders includes a new section on the brain-gut connection, and dives into groundbreaking discoveries of psychobiotics—microbes with psychological effects that can influence mental health conditions like depression and even stress. For too long, the gut has been the body’s most ignored and least appreciated organ. But it does more than just dirty work; it’s at the core of who we are, and this beguiling book will make you finally listen to those butterflies in your stomach: they’re trying to tell you something important.
A visual exploration of the universe that exists within our own bodies. Within our bodies hides an entire world of organisms called microbes. They boost our immune systems, digest our food, regulate our metabolism and even impact on our mental health. Through Katie Brosnan’s personable illustrations, we follow the digestive process from the moment the food enters our mouths to the moment waste leaves our bodies. Along the way we learn about this fascinating scientific frontier and gain an insight into the vast ecosystem that exists inside us.
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This text features coverage of basic intestinal physiology, as well as the management of complications and unusual problems. Additional chapters and fully updated material consider laparoscopic-assisted colostomy and methods of urinary diversion in stoma management.