Department of Physiology and Biophysics, University of Nebraska Medical Center, Omaha, Nebraska
The endothelium of cerebral blood vessels forms the interface between the blood and brain tissue (blood-brain barrier), and is the main physical barrier that minimizes the entry of blood constituents into brain tissue. This restriction by the blood-brain barrier arises by the presence of tight junctions (zonulae occludens) between adjacent endothelial cells and a relative paucity of pinocytotic vesicles within endothelium of cerebral arterioles, capillaries, and venules. Physical, chemical, and metabolic stimuli can alter the permeability characteristics of cerebral endothelium. For example, acute increases in arterial blood pressure beyond the autoregulatory capacity of cerebral blood vessels, application of hyperosmolar solutions, cerebral hypoxia, cerebral ischemia-reperfusion, synthesis/release of inflammatory mediators during brain injury, and/or activation of blood-borne elements can dramatically alter the permeability characteristics of the blood-brain barrier. However, the precise cellular mechanisms that account for maintaining the basal integrity of the blood-brain barrier and stimulus-induced increases in permeability of the blood-brain barrier remain poorly defined. Recent evidence suggests that the synthesis/release of nitric oxide may play a role in the regulation of permeability of the blood-brain barrier. Thus, this review will focus on studies that have implicated an important role for nitric oxide in the integrity of the blood-brain barrier during physiologic and pathophysiologic conditions.
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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.