anatomical sphincter - smooth or skeletal muscle surrounding the lumen of a vessel or hollow organ that can restrict flow when contracted

detrusor muscle - smooth muscle in the bladder wall; fibres run in all directions to reduce the size of the organ when emptying it of urine

external urinary sphincter - skeletal muscle; must be relaxed consciously to void urine

internal urinary sphincter - smooth muscle at the juncture of the bladder and urethra; relaxes as the bladder fills to allow urine into the urethra

incontinence - loss of ability to control micturition

micturition - also called urination or voiding

physiological sphincter - sphincter consisting of circular smooth muscle indistinguishable from adjacent muscle but possessing differential innervations, permitting its function as a sphincter; structurally weak

retroperitoneal - outside the peritoneal cavity; in the case of the kidney and ureters, between the parietal peritoneum and the abdominal wall

sacral micturition centre - group of neurons in the sacral region of the spinal cord that controls urination; acts reflexively unless its action is modified by higher brain centres to allow voluntary urination

trigone - area at the base of the bladder marked by the two ureters in the posterior–lateral aspect and the urethral orifice in the anterior aspect oriented like points on a triangle

urethra - transports urine from the bladder to the outside environment

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