The rectum is the final straight portion of the large intestine in humans and some other mammals. The adult human rectum is about 4.7 inches (12 centimetres) long, and begins at the rectosigmoid junction, which is located at the end of the sigmoid colon.
In humans, the rectum is followed by the anal canal, which is the terminal segment of the large intestine, located between the rectum and anus. Interestingly enough, the word “rectum” comes from the Latin rectum intestinum, meaning straight intestine.
The rectum is part of the lower gastrointestinal tract, a continuation of the sigmoid colon, and connects to the anus. It acts as a temporary storage site for feces. As walls of the rectum expand due to waste materials filling it, stretch receptors located in the rectal walls stimulate the desire to pass feces, a process called defecation.
An internal and external anal sphincter, prevent leakage of feces (i.e., incontinence). As the rectum becomes more swollen, the sphincters relax and contents of the rectum are expelled. This expulsion occurs through contractions of the muscles of the rectum.
Due to the proximity of the front wall of the rectum to the prostate in males (or to the vagina in females), and the nerves shared between them, rectal stimulation or penetration can result in sexual arousal.