The rectum serves a very important function. Equipped with both voluntary and involuntary nerve inputs as well as several layers of highly specialized muscle, the rectum allows the storage of stool until it is appropriate for evacuation. Upon entering the rectum, the firm stool triggers an involuntary reflex that tightens the muscles of the anus. Only with voluntary input can these muscles be relaxed, thereby initiating the process of defecation and evacuation.

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