Incontinence. Artwork showing a section through the urinary system of a woman, with the muscles involved in incontinence (involuntary leaking of urine from the bladder). The bladder is an organ which stores urine (yellow/orange) before its expulsion from the body through the urethra (centre to lower centre). During urination, the muscles in the bladder wall (light pink) contract, whilst those in the internal and external urethral sphincters (dark pink ovals at base of bladder and further down urethra) relax. Incontinence occurs when these muscles fail to contract or relax at the right time, or when the muscles are weak, causing urine to leak from the urethra.