The external anal and urethral sphincters close the anus and the urethra. Constriction of these sphincters reduces or shuts off blood flow through their respective capillary beds. There are two sphincters in the oesophagus. There is a malfunction between the central nervous system, urinary sphincters, and detrusor muscles. These sphincters act to close the esophagus when food is not being swallowed. Sphincters will relax spontaneously and urine and faeces will be evacuated. Sphincters relax at death, often releasing fluids and faeces. It becomes overfilled, and urine dribbles through the sphincters (overflow incontinence). Engineered anal sphincters grown from stem cells have been successfully implanted in mice. In the pre-capillary sector, arterioles, and precapillary sphincters participate. Problems with these sphincters can lead to incontinence. By 2019, more than 4,500 ZSI 375 artificial urinary sphincters have been implanted worldwide. Precapillary sphincters and metarterioles were discovered in the mesenteric circulation in the 1950s. The appearance is of a reddened, proboscis-like object through the anal sphincters. These occur in the sphincters of the tract, as well as in the anterior stomach.