The kinin system is an enzymatic cascade that begins when a plasma clotting factor, called Hageman factor, is activated following tissue injury. The activated Hageman factor then activates prekallikrein to form kallikrein, which cleaves kininogen to produce bradykinin (see Figure 15-10). This inflammatory mediator is a potent basic peptide that increases vascular permeability, causes vasodilation, induces pain, and induces contraction of smooth muscle. Kallikrein also acts directly on the complement system by cleaving C5 into C5a and C5b. The C5a complement component is an anaphylatoxin that induces mast-cell degranulation, resulting in the release of a number of inflammatory mediators from the mast cell.
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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.