Micturition

Micturition, the final phase of excretion of urine from the body, topically related to the urinary bladder and characterized by functional periodicity. The urinary bladder plays the role of a reservoir for urine, continuously flowing into it through the ureters due to their peristaltic contractions; these movements are automatic and depend on the greater or lesser activity of the kidneys. As the urinary bladder gradually fills, it stretches, and the increase in pressure in the bladder does not prevent further penetration of urine into it, which is explained by the oblique location of the ureteral orifices of the bladder; as for the continuous inflow of urine, it is due to the law of the hydraulic press, since the cross-sectional area of the ureters is very small compared to the inner surface of the bladder. On the other hand, the physiological tone of the smooth muscle sphincter of the bladder neck creates an obstacle to the outflow of urine through the urethra. The act of micturition itself is regulated by the neuromuscular apparatus, controlled by reflex and conscious-voluntary spheres. The question of the localization of the urinary bladder center in the cerebral cortex cannot yet be considered finally resolved. Data from experiments on animals and clinical observations allow us to assume the existence of cortical centers for the muscles of organs innervated by the autonomic-sympathetic system, and in particular centers for the sphincter and detrusor of the urinary bladder; these latter centers can be localized close behind the centers of the lower limbs; however, according to Müller's assertion, the existence of such a cortical center contradicts the principles of organization of all other vegetative functions, which do not have localizations in specific parts of the cerebral cortex. The voluntary moment in micturition is explained by Müller as follows: an impulse for the contraction of the striated muscles located under the urinary bladder, as well as for the relaxation of the striated m. compressor urethrae, is transmitted along the pyramidal path, and consequently, a reflex that leads to micturition is played out secondarily in the autonomic nervous system. In general, the act of micturition proceeds in the following sequence: gradually increasing intravesical pressure overcomes the tonic resistance of the urethral sphincter, which determines the passage of drops of urine through the bladder neck and from there into the prostatic part of the urethra; the contact of the mucous membrane of this very sensitive area with urine creates peripheral irritation directed to the brain; this moment is characterized by a special sensation (urge to urinate), which in our consciousness is localized closer to the orificium urethrae; after this, if there is no reason for voluntary retention, urination, emptying of the bladder may occur due to contractions of the bladder wall with relaxed sphincters; these phenomena characterize the reflex phase of micturition, caused by the influence of parasympathetic fibers. In the normal state, the participation of the brain also takes place, which brings about micturition by influencing the bladder musculature through the medium of peripheral ganglia. This innervation is expressed in the duration of the latent period, which is always observed with voluntary micturition, i.e., without a preceding urge. Completely different from this is the influence of the brain on the striated external sphincter of the bladder, which is directly subject to the will. With the help of this muscle, innervated by the p. pudendus, one can suddenly interrupt the stream of urine by compressing the urethra and, despite a strong urge, retain emptying of the bladder at any moment. It should be noted that the act of micturition can occur not only by reflex from the mucous membrane of the bladder or the prostatic part of the urethra, but also from the sensory nerves of other areas of the body, and also occur under the influence of emotional excitations. The need for micturition usually arises when 100-120 cm³ accumulates in the bladder, but it is not directly dependent on the amount of urine contained in the bladder and can sometimes reach a severe degree even with slight stretching of the bladder. The urge to urinate depends on the tone of the bladder (Denning, Schwarz), for example, during sleep the tone of the bladder decreases, therefore, although the bladder fills more and more, the tension of its walls remains below that at which an urge to urinate appears. A decrease in tone is also observed with voluntary suppression of the urge. An increase in tone and, depending on this, a rapid increase in the urge to urinate is observed upon awakening. The awareness of the urge to urinate and the ability to delay urination by compressing the urethra depend on the full development of the corresponding parts of the nervous system, which is why in early childhood urination occurs involuntarily and only by the 2nd year or even later does this function reach its normal state. Pathologically. If we take into account that the coordination of the functions of the detrusor and sphincter when the bladder cavity is irritated by urine is due to the automatic activity of the sympathetic nerve centers of the bladder, the activity of the spinal cord centers, and finally the volitional impulses of the cerebral cortex, then, based on this scheme, we can present the general symptomatology of disorders of micturition in the following basic forms. The release of the urinary bladder from the influence of the spinal cord centers when they or their peripheral conductors are destroyed leads to urinary incontinence (incontinentia urinae); in these cases, the urinary bladder turns into an inert bag, from which urine flows as it fills from the ureters. When the conductors connecting the cerebral cortex with the spinal cord center are damaged, the independent activity of the urinary bladder begins. The first period of such isolation of the spinal cord center will be expressed by a disorder in the coordination of the functions of the detrusor and sphincter: urine will accumulate in the bladder, the detrusor will strive to expel it, but the contracted sphincter will create an obstacle to expulsion - urinary retention (retentio urinae) will occur, and the bladder will be filled with urine, which will stretch the muscle fibers of the detrusor and weaken the tension of the sphincter; from this moment, the outflow of urine drop by drop with an overfilled bladder will begin {ischuria paradoxa, see}. The outflow of urine drop by drop will give way to its flow in separate portions, which will increase in size, and finally a moment will come when the bladder will restore the automatic and coordinated activity of its muscles and the urine, retained by the sphincter after sufficient accumulation, will be expelled by the detrusor without opposition from the sphincter; involuntary periodic excretion of urine in large portions will begin. - Diseases of the brain can also cause disorders of micturition in the form of both incontinence and retention; weakening or loss of volitional impulses to retain urine creates conditions for reflex micturition; more often, usually with diseases of the brain, during the comatose state of patients, urinary retention is observed as a result of the suppression of all reflex activity in general. The above-mentioned disorders of micturition can occur both on the basis of organic lesions of the nervous system that destroy its elements, and on the basis of functional diseases that introduce a temporary disorganization into the coordinated activity of the apparatus as a whole and its parts. Thus, with hysteria and neurasthenia, urinary incontinence can be observed, usually in the form of frequent urges to urinate - pollakiuria (syn. thamuria), the dissatisfaction of which inevitably leads to involuntary urination. Various emotional moments can also serve as a reason for various forms of disorder of micturition. With physical pain, involuntary urination occurs; with laughter and crying, involuntary excretion of urine can also occur - a symptom formerly denoted by the term (now rarely used) dacryuria. Spastic forms of disease of the bladder musculature (tenesmus of the bladder) can cause painful urination with phenomena of its retention and excretion drop by drop - stranguria (syn. stillicidium urinae). Nighttime urinary incontinence, enuresis nocturna (see), should be considered somewhat separate in its pathogenesis.

A. Surov