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The Gastrointestinal Circulation

2010 Medical
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Release : 2010
Genre : Medical
Kind : eBook
Book Rating : 176/5 ( reviews)

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Book Synopsis The Gastrointestinal Circulation by : Peter R. Kvietys

Download or read book The Gastrointestinal Circulation written by Peter R. Kvietys. This book was released on 2010. Available in PDF, EPUB and Kindle. Book excerpt: 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

Regulation of Tissue Oxygenation, Second Edition

2016-08-18 Medical
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Release : 2016-08-18
Genre : Medical
Kind : eBook
Book Rating : 212/5 ( reviews)

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Book Synopsis Regulation of Tissue Oxygenation, Second Edition by : Roland N. Pittman

Download or read book Regulation of Tissue Oxygenation, Second Edition written by Roland N. Pittman. This book was released on 2016-08-18. Available in PDF, EPUB and Kindle. Book excerpt: This presentation describes various aspects of the regulation of tissue oxygenation, including the roles of the circulatory system, respiratory system, and blood, the carrier of oxygen within these components of the cardiorespiratory system. The respiratory system takes oxygen from the atmosphere and transports it by diffusion from the air in the alveoli to the blood flowing through the pulmonary capillaries. The cardiovascular system then moves the oxygenated blood from the heart to the microcirculation of the various organs by convection, where oxygen is released from hemoglobin in the red blood cells and moves to the parenchymal cells of each tissue by diffusion. Oxygen that has diffused into cells is then utilized in the mitochondria to produce adenosine triphosphate (ATP), the energy currency of all cells. The mitochondria are able to produce ATP until the oxygen tension or PO2 on the cell surface falls to a critical level of about 4–5 mm Hg. Thus, in order to meet the energetic needs of cells, it is important to maintain a continuous supply of oxygen to the mitochondria at or above the critical PO2 . In order to accomplish this desired outcome, the cardiorespiratory system, including the blood, must be capable of regulation to ensure survival of all tissues under a wide range of circumstances. The purpose of this presentation is to provide basic information about the operation and regulation of the cardiovascular and respiratory systems, as well as the properties of the blood and parenchymal cells, so that a fundamental understanding of the regulation of tissue oxygenation is achieved.

Anatomy and Physiology

2013-04-25
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Release : 2013-04-25
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Kind : eBook
Book Rating : 807/5 ( reviews)

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Book Synopsis Anatomy and Physiology by : J. Gordon Betts

Download or read book Anatomy and Physiology written by J. Gordon Betts. This book was released on 2013-04-25. Available in PDF, EPUB and Kindle. Book excerpt:

Mesenteric Vascular Disease

2014-11-20 Medical
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Release : 2014-11-20
Genre : Medical
Kind : eBook
Book Rating : 478/5 ( reviews)

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Book Synopsis Mesenteric Vascular Disease by : Gustavo S. Oderich

Download or read book Mesenteric Vascular Disease written by Gustavo S. Oderich. This book was released on 2014-11-20. Available in PDF, EPUB and Kindle. Book excerpt: This book represents the first comprehensive textbook devoted to the standard of care, current guidelines and innovations in the field of mesenteric vascular disease. The book reviews imaging modalities, diagnostic work up, physiologic tests, traditional open surgical techniques and novel endovascular approaches. Technical aspects of both open surgical and endovascular techniques are provided by experts in the field, with illustrations and photographs of key steps for each type of procedure. Results of epidemiologic studies and national databases are summarized, as well as large institutional experiences. An evidence-based approach is used for recommendations regarding best therapies. Diagnostic approaches including imaging and novel physiologic tests, including gastric tonometry and oxygen light spectroscopy are covered. Mesenteric Vascular Disease: Current Therapy will serve as a very useful resource for clinicians, surgeons, interventionalists, gastroenterologists and researchers dealing with and interested in mesenteric vascular diseases.

Colonic Motility

2010-11-01 Medical
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Release : 2010-11-01
Genre : Medical
Kind : eBook
Book Rating : 516/5 ( reviews)

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Book Synopsis Colonic Motility by : Sushil K. Sarna

Download or read book Colonic Motility written by Sushil K. Sarna. This book was released on 2010-11-01. Available in PDF, EPUB and Kindle. Book excerpt: 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.

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