Tissue injuries such as wounds and burns are repaired through a series of reparative processes. Depending on the extent of tissue damage, tissue repair may include inflammatory phase. In the inflammatory phase, mast cells release histamine that increases permeability to white blood cells such as neutrophils and phagocytes. Inflammation becomes necessary when the damage on the skin leads to an increased microbial invasion. In order to destroy microorganisms, white blood cells are needed to fight them off. White blood cells (phagocytes) are also important in cleaning up damaged and necrotic cells and thus provide a larger space for blood vessel and cell regeneration. Histamine also increases capillary permeability that leads to extravasation of fluid. Thus, blood proteins, such as fibrinogen, also increase in number at the site of damage. Fibrinogen is a soluble protein in blood plasma that is converted to fibrin through the action of thrombin during blood clot formation. An exudate containing a large amount of fibrinogen and fibrin is described as fibrinous. This type of exudate is seen in rheumatic carditis, strep throat, and bacterial pneumonia.
Word origin: fibrinous, from fibrin (from Latin fibra meaning fiber + -in) + -ous + exudate, from exude meaning to ooze," which came from the Latin exsūdāre (to sweat out, i.e. ex- meaning out and sūdāre meaning to sweat)