DISSOCIATION

DISSOCIATION (from Latin dissociare - to separate), separation. In pathology, the term D. is used in a dual sense: on one hand as a morphological concept, denoting the separation, displacement of various tissue elements from one another, which results in the disruption of the normal tissue structure; on the other hand - one can speak of functional D., implying by this a disruption of the functional relationship between different organs or different parts of one organ. D. in the morphological sense is observed, for example, in bundle connective tissue, expressed in the delamination of its bundles, i.e., the displacement of collagen fibrils from one another, which occurs, for instance, in edema. Further, D. often occurs in the epithelial covering, where it manifests as the separation of epithelial cells from one another and the resulting disruption of the normal complex state of the epithelium; such a change in the epithelium may be a result of mechanical influences or more often occurs when the epithelial covering is impregnated with fluid, for example, inflammatory exudate, which loosens the cementing substance (Kittsubstanz) between the cells; in such cases, D. leads to the detachment, desquamation of epithelial cells. Similarly, in parenchymal organs, as a result of loosening of the reticular tissue, dissociation of cells occurs; in particular, in the liver, D. is expressed in the fact that the cells no longer form trabeculae, but are arranged without any order, separately. D. of elements of various tissues (connective, epithelial, muscular) can occur when a tumor grows between these elements. - Functional D. mainly concerns the activity of the heart and is expressed in the fact that under the influence of disruption of the continuity of the atrioventricular bundle, there is a disruption of the normal sequence in the contractions of different parts of the heart (see Heart block, Longitudinal dissociation).