Organization

Organization (in pathology), the process of replacement through living 'organized' tissue of any dead material. The latter may form within the body itself (e.g., thrombi, hemorrhages, exudates, infarcts, foci of necrosis) or represents a foreign body that has entered the tissue from outside. In essence, such O., also called pathological O., belongs to the manifestations of regeneration (see). Along with this, it is extremely closely connected with inflammation (see), and the separation of pathological O. from inflammation has only conditional significance, not having any basis for a difference in the essence of these processes. The physiological prototype of pathological O. is the replacement of the corpus luteum of the ovary by connective tissue. Schematically, the process of O. proceeds as follows. Its beginning is the demarcation inflammatory reaction that arises in the tissue directly bordering the dead substrate, and is manifested by hyperemia, the secretion of serous or fibrinous exudate, and the emigration of leukocytes; the latter, accumulating directly on the border with the dead material, as well as penetrating with the exudate into the dead mass if the physical properties of the latter permit this, enhance by their enzymes the process of autolytic softening of the dead material; the phenomena of phagocytosis of particles of the softening dead substrate by wandering cells observed along with this lead to the gradual resorption of the dead mass. Along with all these manifestations of the exudative inflammatory reaction, there occurs the multiplication of local cells and the new formation by budding of young blood vessels, which together gives rise to the formation of granulation tissue; the latter gradually grows over the dead material, penetrates it in strands, and little by little replaces it. The degree of replacement of the dead material by granulation tissue depends on the physical properties of the latter and on whether it can undergo softening and resorption. For example, thrombi, hematomas with clotted blood, exudates, infarcts with a small volume are easily subjected to softening, resorption, and can be completely replaced by granulation tissue. In contrast to this, areas of dead bone, dense foreign bodies can undergo resorption only to a very slight degree or are completely incapable of it, due to which in relation to them O. is expressed not in the complete replacement of the dead material by newly formed tissue, but only in its encapsulation. Subsequently, the granulation tissue that has replaced the dead substrate or encapsulated it, undergoing maturation, gradually transforms into scar connective tissue. Deviations from this course of O. may occur: for example, sometimes the dead material does not undergo softening and resorption, or due to changes in the environmental conditions or the pace of the inflammatory reaction, the softening that has begun stops, and the dead mass shrinks; in such cases the dead substrate is not completely replaced by granulation tissue and is only encapsulated, and often petrified. In other cases, for example in the brain, conversely, due to the peculiarities of the environment, the processes of softening lead to rapid liquefaction of the dead mass, which gives rise to the formation of a cavity filled with liquid decay; under such conditions O. is expressed only in the formation of a capsule around such a cyst. The most frequent examples of O. are the following: O. of fibrinous exudates secreted onto the serous coverings of the pleura, pericardium, peritoneum; it proceeds with the softening of fibrin and its replacement by granulation tissue. The transition of the latter into scarification results in fibrous thickening of the serous membranes, the formation of adhesions (see Adhesion) and obliteration (see Obliteration) in the serous cavities. In O. of fibrinous exudate in the pulmonary alveoli, the latter are overgrown with connective tissue, which leads to the carnification of the pulmonary tissue. O. of thrombi occurs by the ingrowth of young connective tissue into the thrombus from the intima of the vessel; as a result of O. of mural thrombi, fibrous thickenings of the inner lining of the vessel remain; O. of an occluding thrombus leads to the complete obliteration of the vessel, i.e., to its transformation into a solid connective tissue strand without a lumen; in some cases during O. of a thrombus, its canalization (see Canalization in pathology) occurs. O. of clotted blood in hematomas, foci of various necroses, infarcts proceeds with the combination of the processes of softening of the dead mass and its replacement by granulation tissue growing from the neighboring tissue; with a small volume of the focus undergoing O., a scar forms in its place; this includes scars-callosities of the heart after focal myomalacia of it, scars of the kidneys, spleen after infarcts, etc._:-Organization of foci of wet necrosis is expressed in the formation of an encapsulated cyst. In O. of old abscesses, the organizing proliferation of granulation tissue originates from the so-called pyogenic membrane and sometimes gives rise to the formation on the site of the abscess of a scar with groups of xanthoma cells or a capsule around the condensed, often amorphous necrotic mass.-O. of foreign bodies- see Encapsulation.