Pathogenesis of urination disorders

To understand the pathogenesis of micturition and defecation with different levels of damage to systems that regulate them, we must first of all focus on the innervation mechanisms of the bladder and rectum.

The function of stretching the bladder with the accumulation of urine and its contraction during emptying is carried out by a smooth muscle detrusor. Synergists of detrusor during emptying are the muscles of the abdominal press and perineum. The exit of the bladder into the urethra is closed by two sphincters - smooth muscle inner and striated external. Detrusor and sphincters function reciprocally: when the bladder is emptied, the detrusor is reduced and the sphincters are relaxed, when the bubble is closed, the ratios are reversed, that is, the detrusor relaxes and the sphincters contract.

Control of the function of the bladder is predominantly parasympathetic. The spinal parasympathetic center of the bladder is located in the cone of the spinal cord, in the nuclei of the lateral horns of the sacral segments of SII-SIV.

Fibers of nuclei pass first in the structure of the plexus nerve plexus, then go on both sides of the rectum and, joining the hypogastric sympathetic nerves, form a plexus plexus. Postganglionic parasympathetic fibers innervate the smooth muscles of the bladder, its neck, urethra. Part of the preganglionic nerves terminates in the intramural ganglia in the thickness of the bladder, causing automatic urination with partial or complete denervation of the bladder. In general, parasympathetic stimulation is accompanied by a reduction in detrusor and relaxation of the internal sphincter. As a result, the bladder is emptied. Damage to the parasympathetic pathway leads to atony of the bladder.

Preganglionic sympathetic nerve fibers begin in the intermediolateral nuclei of the lateral horns of the spinal segments TXI, TXII, LI, LII. Some of them, having passed through the sympathetic trunk, terminate in the lower mesenteric and hypogastric plexuses. Postganglionic neurons are sent from here to the smooth muscles of the wall of the bladder and internal sphincter. The other part of the preganglionic sympathetic nerves terminates in the plexus plexus around the neck of the bladder or in the intramural ganglia of the bladder wall.

Histochemical studies revealed a large number of adrenergic nerve endings in the entire bladder and urethra, especially in the base of the bladder and the proximal part of the urethra (a-adrenergic receptors), less in the body of the bladder (alpha-adrenergic receptors). Stimulation of alpha-adrenoreceptors causes an increase in the output resistance (reduction of the internal sphincter), and stimulation of beta-adrenoreceptors leads to relaxation of the body of the bladder (detrusor relaxation). In animal experiments, the presence of alpha-adrenergic receptors in the parasympathetic ganglia of the detrusor was demonstrated. It is assumed that sympathetic control of the bladder is mediated by sympathetic influences on the transmission in the parasympathetic ganglia. Thus, sympathetic stimulation causes relaxation of the detrusor and reduction of the internal sphincter, which leads to an increase in the filling of the bladder and inhibition of the evacuation of urine from it. It is believed that the defeat of sympathetic nerves does not lead to pronounced impairment of urination.

The external sphincter of the bladder is a striated muscle and receives somatic innervation due to the cells of the anterior horns of the sacral segments (SII-SIV). Despite the fact that it is under arbitrary control, its opening occurs only during the passage of urine through the internal sphincter, while it remains open until the bladder is completely emptied.

Afferent impulses from the bladder are carried by hypogastric nerves, the sensitivity of the urethral part of the mucosa is determined by the pelvic and pudendal nerves. Some of these fibers go to the hindbusts of the spinal cord, participating in the formation of a spinal reflex arc (at the level of SII-SIV), part of it rises in the composition of thin beams (Gaul's bundles) to the brain, providing a feeling of urge to urinate and its arbitrary existence.

The cortical center of urination, according to most authors, is localized in the paracentral lobe. There is also an opinion about its localization in the anterior central gyrus, in the region of the hip muscle center. Corticospinal fibers pass in the anterior and lateral columns of the spinal cord and have a two-way connection with the spinal nuclei. Subcortical centers are located in the visual hillock, hypothalamic region and some other departments. Studies in this area are not yet complete.

Thus, the function of the bladder is based on spinal reflexes, which, when emptied and closed, are in reciprocal relationships. These unconditioned reflexes are subordinated to the cortical effect, which already by the principle of the conditioned reflex causes an arbitrary urination.

The anatomical and functional relationships of the act of defecation are similar to urination. Exit from the rectum is closed by a smooth-muscle internal sphincter, functioning involuntarily, and a cross-striated external sphincter acting arbitrarily. Auxiliary role in this play the muscles of the perineum, especially m.levator ani. Getting into the rectum, stool masses reflexively cause peristalsis due to the contraction of its longitudinal annular muscles and the opening of the internal sphincter receiving parasympathetic innervation from the nuclei of the II-IV sacral segments. These fibers are part of the pelvic nerves. The sympathetic nerves that began in the intermediolateral nuclei of the lateral horns of I-II lumbar segments approach the smooth-muscle internal sphincter. Sympathetic stimulation leads to inhibition of peristalsis. The external arbitrary sphincter of the rectum receives impulses from the anterior-horn apparatus of the spinal cord through the pudendal nerve.

In the rectum wall, as well as in the bladder, there is an intramural plexus, due to which an autonomous function of the rectum can be performed in conditions of its denervation.

Sensitive fibers from the rectum pass into the spinal cord through the back roots. One part of these fibers participates in the formation of the spinal reflex arc, the other rises in the brain, causing a sense of urging on defecation. The cortical center of defecation, according to the majority of authors, is localized in the upper part of the anterior central gyrus. Conductors from the cortex to the spinal centers pass in the anterior and anterolateral columns of the spinal cord. The subcortical apparatus is located in the hypothalamus, the nuclei of the brain stem. Afferent impulses that enter the cortex arise when the stool passes into the rectum and advances toward the anal opening. Defecation can be arbitrarily delayed by reducing the striated muscles of the pelvic floor and the external sphincter. An arbitrary act of defecation is carried out in conditions of peristalsis of the rectum, relaxation of the smooth-muscular inner sphincter and opening of the external sphincter. At the same time, the muscles of the abdominal press are synergistically reduced.

The unconditioned reflex activity of the spinal reflex arc during defecation, as well as during urination, is under constant control of more complex upstream mechanisms, in particular, the cortical center, whose function is determined by the corresponding conditions. The pathogenesis of urination disorders is the violation of the relationships examined as a result of structural defects with various lesions of the nervous system that lead to disorders of urination and defecation, combined in conditions of pathology.

[1], [2], [3], [4], [5], [6], [7]