Defecation is a complex, neurally controlled act that includes voluntary and involuntary elements. Mass movements or coordinated segmental contractions of the colon deliver fecal matter to the rectum. Stretch receptors in the wall of the rectum and anal canal respond and trigger the rectosphincteric reflex. Afferent signals are sent to the cerebral cortex, where the urge to defecate is recognized, to the autonomic ganglia, and to the spinal centers, which provide the efferent innervation of the sphincters. As distension increases, rectal contractions are reflexly induced. When the rectum is distended, the immediate reflex response is relaxation of the internal sphincter and contraction of the external sphincter. If conditions are perceived to be appropriate (ie, socially acceptable) for defecation, the external sphincter is voluntarily relaxed and defecation occurs. If conditions are inappropriate, contraction of the external sphincter is voluntarily maintained, the rectal stretch receptors adapt, and the rectum relaxes to accommodate the contained fecal matter. The act of defecation is facilitated by assuming a squatting or seated position to align and dilate the recto-anal junction and by employing the Valsalva maneuver to increase intra-abdominal pressure.