University of Western Ontario, London, Canada
Gap junctions, found in nearly all mammalian cells, are intercellular channels that permit a direct passage of ions and small molecules (up to 1 kDa molecular mass) between the cytosols of adjacent cells. Gap junctional communication between the cells of vascular wall has been proposed to coordinate microvascular function, including participation in the local control of blood flow.
Conceptually, the local control serves to match the local tissue blood flow to the tissue's metabolic demand. Vasoac-tive metabolites generated within the tissue during periods of demand are envisioned to reach upstream arterioles to cause adjustment of arteriolar diameter and blood flow to meet this demand. However, for tissues where the distance between the site of demand and upstream arterioles is large (e.g., distances along skeletal muscle fibers can be of the order of 1 mm), it is not clear how metabolic signals reach these arterioles. Since simple diffusion of metabolites across these distances may be too slow in relation to the speed of observed vasomotor responses, a new mechanism of matching the arteriolar response to the local demand has been proposed . This mechanism is hypothesized to involve metabolically induced electrical signals that spread along the capillary endothelium to the arteriole via gap junctions (i.e., capillary-arteriolar communication). The present chapter discusses the available evidence regarding this mechanism and examines how the pathological condition of systemic inflammation could affect this communication.
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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.