This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
[{'content': 'Defecation reflex is intiated by? \nSelect and explain. \nA. Distension of rectum with feces., B. Post-prandial motility in duodenum, C. Only during diseased state, D. All of the above', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Defecation reflex initiated by distension of rectum with feces. Defecation reflex: Initiated by distension of rectum with feces. Leads to propulsive wave extending from descending colon through sigmoid colon to rectum Urge to defecate is first felt when rectal pressure increases to about 18 mm/Hg. On reaching 55 mm/Hg rectal pressure - "Rectoanal inhibitory reflex" - Internal sphincter relaxes reflexly.', 'role': 'assistant'}]