Dilatation

DILATATION (Latin for expansion), the expansion of any hollow organ. The causes and mechanism of dilatation of organs are very diverse. Thus, dilatation of an organ can occur due to the retention of secretions or contents due to narrowing or closure of the excretory duct or canal (e.g., D. of the gallbladder in obstruction of the bile duct, D. of the urinary bladder in hypertrophy of the prostate or strictures of the urethra, D. of the brain ventricles in difficulties of outflow of cerebrospinal fluid). Another type of cause of D. is weakening of the muscle tone, e.g., of the heart, on the basis of degenerative changes in the myocardium, which is observed in decompensated heart defects, emphysema of the lungs (D. of the right heart), in cardiac overexertion (e.g., in cyclists) and so on. D. of an organ can develop on the basis of spasm of a sphincter, e.g., D. of the esophagus in cardiospasm. D. ventriculi occurs in various diseases of the stomach and is observed, for example, in stenoses of the pylorus that have arisen on the basis of scarring from a round ulcer, in cancers of it, pylorospasm, hypertrophy of the pylorus and so on. Cases of D. of organs of congenital origin deserve special mention, e.g., D. of the esophagus or large intestine on the basis of abnormal development of their walls. However, in most of these cases, it is not so much about a congenitely wide lumen as about excessively large dimensions of the organ (manifestation of partial gigantism). DILATATION-REFLEX, dilation of the pupils in response to sudden painful irritation. The dilation of the pupils here apparently occurs due to inhibition of the center for pupil constriction reflex located in the nuclei of the n. oculomotorii (Bechterev), while dilation of the pupils in emotions is the result of direct excitation of the sympathetic cervical nerve, which contains fibers that dilate the pupil. The pupillary dilatory reflex to pain has certain diagnostic value, helping to differentiate true analgesia from hysterical or simulated analgesia. In true analgesia, the dilation of the pupils in response to painful stimulation is absent.