Abstract
The lower urinary tract (LUT) is comprised of the bladder and outflow tract whose functions are normally integrated by the central nervous system to allow urine storage and occasional volitional voiding. To achieve this bifunctionality, the bladder is compliant during storage, and the outflow tract maintains a high fluid resistance to prevent leakage. Conditions are reversed during voiding when the bladder generates a substantial intravesical (detrusor) pressure preceded by a fall of outflow resistance. In addition, reflux into the ureter is minimized by the vesicoureteric junction acting as a nonreturn valve. Control of bladder contractile activity is a key therapeutic goal to manage common benign LUT disorders, and consideration is given to methods, based on lessons from cardiology, that estimate changes to detrusor contractility that may be associated with over- or underactive bladder disorders. Many bladder disorders result from replacement of mucosal and detrusor tissues with connective tissue, and attention is given to the nature of fibrosis and therapeutic strategies to reverse this pathology. Contractions arising from the detrusor layer are generally evoked by efferent nerve activity but are overlain by spontaneous contractions, whose magnitude can be as large as evoked contractions in pathological conditions. The cellular physiology of these modes of contraction is considered, including potential roles for ubiquitous interstitial cells, as well as the interaction between the detrusor and mucosa. The outflow tract is considered as an interactive unit of trigone, urethral wall tissues, and striated muscle of the external urethral sphincter that together can achieve their function to offer high or low fluid resistances during the micturition cycle. Finally, the structure and function of the pelvic floor musculature is described, and it serves as an accessory continence structure.
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Fry, C.H., Jabr, R.I. (2023). The Integrated Physiology of the Lower Urinary Tract. In: Liao, L., Madersbacher, H. (eds) Handbook of Neurourology. Springer, Singapore. https://doi.org/10.1007/978-981-99-1659-7_7
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