Function of the Lower Urinary Tract and its Disorders
Zachoval R. 1 , Záleský M. 1 , Lukeš M. 1 , Mareš J. 2 , Urban M. 1 , Palascak P. 3
1 Urologická klinika 3. LF UK Praha 2 Ústav normální, patologické a klinické fyziologie 3. LF UK Praha 3 Urologické oddělení, nemocnice Paul Morel, Vesoul, Francie |
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Summary:
The lower urinary tract provides two modes of operation – storage and elimination of urine. The normal function
results in the coordination of contraction and relaxation of muscles of the urinary bladder and urethral
sphincters. Disorders of these activities or their interaction lead to the development of lower urinary tract
dysfunctions. The nervous system plays an essential role in the regulation of the functions. The control of
micturition is coordinated by several regious of the central nervous system. Afferents and efferents of the periferal
nervous system carry signals from and to the lower urinary tract.
The reflex circuitry controlling micturition consists of five components: spinal efferent neurons, peripheral
efferent neurons, primary afferent neurons, spinal interneurons and neurons in the brain.
Preganglionic neurons located in the sacral parasympathetic nucleus and lumbar sympathetic nucleus excite
the peripheral efferent neurons innervating smooth muscles of the urinary bladder and urethra. Motoneurons
of sacral Onuf’s nucleus excite the striated muscle of the external urethral sphincter.
Myelinated and unmyelinated afferent axons transmit information from the lower urinary tract to the lumbo-
sacral spinal cord. Three receptor types of the lower urinary tract are present: tension receptors, volume receptors
and „silent receptors“, which become nociceptors following the senzitization. Afferent pathways terminate on
spinal interneurons.
Spinal interneurons relay information to the brain or to other regions of the spinal cord. Because micturition
reflexes are mediated by disynaptic or polysynaptic pathways, interneuronal mechanisms are of crucial
importance in the regulation of lower urinary tract.
Central pathways involved in micturition reflexes are located in spinal and supraspinal areas. Micturion reflexes
can be modulated at the level of the spinal cord by viscero – bladder and somato – bladder reflexes. Supraspinal
areas have a more complicated organization: critical component of the micturition reflex is the pontine
micturition center and the periaqueductal gray. Inhibitory and excitatory areas in the pontomedullary and
hypothalamic systems and the brain play an important role in the regulation of micturition reflexes.
Key words:
lower urinary tract, function, disorders
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