The response of blood vessels to injury is made up of a series of interrelated reactions involving endothelial cells, platelets, and proteins of the coagulation, complement, kinin, and fibrinolytic systems, all of which may directly or indirectly contribute to the inflammatory process. Inflammation may in turn contribute to thrombosis and atherosclerosis through the complement system, or via inflammatory cytokines secreted by activated macrophages and lymphocytes present at inflammatory sites, atherosclerotic plaques, and sites of vascular injury. The inflammatory process, which begins as a protective response, is therefore the result of multiple interactions including those that involve the complement system and the coagulation cascade.
In addition to its role of maintaining vessel wall integrity, the endothelium plays a critical role in the pathophysiology of thrombosis, atherosclerosis, and inflammation. This is largely due to the ability of endothelial cells to respond to a wide range of signals that include microbial proteins, cytokines, growth factors, and proteins of the complement system and the kinin-forming cascade. Some of these responses are rapid and do not require new gene transcription or protein synthesis. These responses, which are the hallmark of the early nonleukocyte-dependent phase of inflammation, include expression of surface P-selectin, activation of nitric oxide (NO) metabolic pathways, and enhanced vascular permeability. A large number of agonists are capable of eliciting this type of response, including proteins of the clotting and complement systems. Vasoactive peptides derived from both of these systems can in turn recruit proinflammatory cells into the inflammatory site, thus exacerbating the disease process.
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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.