During mass movement, an urge to defecate occurs when what happens?

• A. The stomach empties
• B. The ileocecal valve relaxes
• C. The ingested food reaches the rectum
• D. The colon becomes fully distended

Answer: (C)

Mass movement moves fecal matter toward the rectum, and the urge to defecate comes from the rectum being stretched by those contents. When the rectal walls distend, stretch receptors trigger the reflex that relaxes the internal anal sphincter and signals the need to defecate. So the key trigger is the arrival of the contents in the rectum and the resulting rectal distension. Other GI events like stomach emptying or ileocecal valve relaxation influence motility, but they don’t directly cause the urge to defecate; colon distension alone isn’t the immediate trigger—the rectal distension from contents reaching the rectum is.