BECs express well-developed adherens and tight junctions that contain both cadherin-5 (vascular endothelial (VE) cadherin) and N- and P-cadherins. VE-cadherin appears to be expressed by both BECs and LECs. While BEC maintain conventional adherens and tight junctions at endothelial borders that regulate solute exchange, LEC junctions form a specialized type of adherens junction termed the complexus adherentes, that contains high levels of plakophilin-2, a desmosomal protein found in nonclassi-cal adherens junctions. Besides plakophilin-2, cadherin-13 and zona occludens 2 (ZO-2) also appear to be elements of the LEC complexus adherentes junction. Desmoplakins have been reported in LECs, but have also been reported in venous BECs and may be an unreliable marker for discriminating BEC from LEC . Despite the proposition that LECs lack the same level of junctional integrity as BECs, podoplanin found within the overlapping cell borders of LEC may help create the LEC capillary "valves," which support the opening and closing of these vessels without the need to remodel tight or adherens junctions . Junctional adhesion molecule-2 (JAM-2) is a junctional component within the CTX [cortical thymocyte Xenopus (CTX) molecular family] that is shared by both high endothelial venule EC and LEC. JAM-2 supports lymphocyte extravasation from the blood vascular space , but its function in lymphatics is not clear. Most likely JAM-2 expressed on HEV and lymphatics plays a role in lymphocyte targeting in that JAM-2 on these endothelium binds to JAM-3 expressed on T, NK, and dendritic cells. Unlike JAM-2, JAM-1 appears to be associated with tight junctions in conjunction with occludin and claudins.
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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.