ABSTRACT
Micturition describes a dynamic process that alternates between phases of storage and expulsion of urine stored in the urinary bladder. The storage phase typically extends for hours, whereas the expulsion phase lasts for a few seconds. Reciprocal contraction and relaxation of smooth muscle in the bladder and urethra is required for these two phases of different duration to happen, which is accomplished by the complex interactions among smooth muscle, connective tissue, urothelium, and supportive structures with innervation. The relay of afferent input from the bladder to the neural circuitry in the brainstem, in particular the periaqueductal gray (pag) and the pontine micturition center (pmc), switches on the periodic transformation of the lower urinary tract from the mode of bladder filling to voiding [1–3] (figure 23.1). The volitional control over this dynamic process is lacking in infants, but is gained through learning by the age of 5 in most individuals. The micturition in both sexes is influenced by neural, biomechanical, biochemical, and morphologic properties of the bladder and urethra, as well as the hormonal influences and unique pelvic and perineal anatomy [4].
