Describe the defecation reflex. Include the following in your answer : rectum, external anal sphincter, mass movement, and internal anal sphincter
What will be an ideal response?
The defecation reflex begins when mass movements of the colon move feces into the rectum, causing it to distend and stimulate stretch receptors in the rectal wall. This reflex causes the internal anal sphincter to relax and the rectum and sigmoid colon to contract more vigorously. If the external anal sphincter (which is skeletal muscle) is also relaxed, defecation occurs. The initial distension of the rectal wall is accompanied by the conscious urge to defecate. If circumstances are unfavorable for defecation, voluntary tightening of the external anal sphincter can prevent defecation despite the defecation reflex.
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