Department of Molecular and Cellular Physiology, Louisiana State University Health Sciences Center, Shreveport, Louisiana, and Department of General Surgery, University of Münster, Münster, Germany
More than 25 percent of cardiac output normally flows through the gastrointestinal tract. However, the rate of blood perfusion through the gastrointestinal (GI) tract is dynamic, responding to both the metabolic requirements of local tissue and the needs of vital organs. For example, the ingestion of a meal is associated with large increases in GI blood flow, while profound reductions in flow are elicited by stresses (e.g., hemorrhage) that threaten to deprive the brain and heart of their normal blood supply. Although blood vessels in the different organs comprising the GI tract share common mediators and mechanisms of blood flow regulation, some differences related to tissue function have been demonstrated. The vascular supply to the gastrointestinal mucosa is particularly well suited for the absorptive and secretory functions of this tissue in that it allows for a high rate of blood flow, has a large exchange surface area, and exhibits characteristics that allow for easy permeation of nutrients and water, yet proteins are largely retained within the plasma compartment. Disease processes affecting the GI circulation can be associated with either impaired blood perfusion (e.g., ischemia) or over-perfusion (portal hypertension).
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.