DEFECATION (Latin. defaecatio clarification) — the complex-reflex act of removal from intestines of fecal masses. Can be subdivided into two interconnected phases — afferent (formation of a desire) and effector (an excrement of fecal masses). The desire to D. appears only at a certain degree of irritation of receptors of a rectum and a pelvic bottom fecal masses, a cut amplifies with receipt of each their new portion from a sigmoid gut. Being one of forms of «the main inclinations» an organism (see. Motivations ), the desire to D. as a certain subjective state evolves from the afferent vozbuzhdeniye going to c. the N of page from a rectum, also forms hl. obr. at the level of a hypothalamus and limbic structures of a brain. Initiation of subcrustal educations at a desire to D. go to bark of big cerebral hemispheres, the center D. and, in particular, to area of the central front crinkle. The desire to D. usually is followed by emotions of unpleasant character. Cortical neurons are capable to influence also in the descending direction subcrustal mechanisms of formation of a desire to D., braking or strengthening it. At the child since the early childhood develop a conditioned reflex for a while owing to what D. occurs daily in the known hours. This conditioned reflex manages to be developed also at domestic animals. Can be caused in an animal in the conditioned-reflex way as a result of a numerous combination of some indifferent irritant (a sound, light) to the act of defecation.
However even in the presence of a desire to D. fecal masses keeps in a rectum. It occurs at the expense of the constant tonic tension of two proctal sphincters — outside and internal (see. Rectum ). The act of an excrement happens reflex. Impulses from receptors of a rectum on a sexual nerve are transferred in a spinal cord; the central impulses causing relaxation of sphincters from the center D. pass on hypogastric nerves. At the same time there occurs reduction of ring muscles of a wall of a rectum, and also bystry shortening of a distal piece of a large intestine in connection with reduction of m. rectococcygeus. Rectum emptying is promoted by breath holding, tension of a prelum abdominale, diaphragm and muscles of a pelvic bottom.
The subsequent closing of sphincters comes under the influence of centrifugal impulses to a rectum from the III—IV sacral segments of a spinal cord on pelvic nerves. Section of a spinal cord of lumbar level gives to paralysis of proctal sphincters (the gaping anus) and impossibility of deduction a calla below. Cortical mental influences, and also the emotions of unpleasant character suppressing a desire to D. can significantly disturb the subsequent rectum emptying. The long and often repeating delays of desires to D. can lead to a perversion of vegetative regulation of an internal proctal sphincter and development locks (see). Therefore for normal D. very important daily regular, at the same time, bowel emptying, is better at once after feeling of a desire.
D.'s frequency is various at different types of animals. So, at horses number D. in day from 5 to 12, at ruminant — from 10 to 20. The person has a frequency of 1 — 2 times a day.
Some strong emotional states (e.g., fear) can lead to involuntary relaxation of both proctal sphincters («a bear disease»). Under the influence of influence of a number of toxicants increase of desires to D. is observed (see. Ponosa ), and also a perversion of normal ratios between a desire and the full act of an excrement (false desires at dysentery). Can stimulate some hormones, napr, Pituitrinum, Thyreoidinum, sincaline.
Bibliography: Physiology of digestion, under the editorship of A. V. Solovyov, page 538, L., 1974.
K. V. Sudakov.