Anorectal anatomy and physiology.

The rectum and anal canal form the last portion of the gastrointestinal tract. The rectum serves as a reservoir for fecal contents, and the anal canal regulates continence and defecation via synchronization of events regulated by complex interactions between sympathetic and parasympathetic nerves, striated and smooth muscle, and environmental factors. Normal function can be compromised by various pathologies. Investigation into these pathologies includes a detailed history and thorough physical exam and can be augmented by a number of different studies, including manometry, electromyelography, defecography, nerve stimulation, and compliance. Some of these techniques have incorporated the use of ultrasound and magnetic resonance imaging.