What Triggers the Defecation Reflex

Question

What triggers the defecation reflex?  
A) Contraction of the colon
B) Stretching of the rectum
C) Voluntary contraction of a sphincter
D) Emotional stress and a diet low in fiber
E) Sufficient concentration of feces due to water removal

Accepted Answer

The defecation reflex is triggered by stretching of the rectum. When feces accumulate in the rectum, the rectal walls stretch, which activates sensory receptors that send signals to the spinal cord. These signals trigger the defecation reflex, stimulating the smooth muscles of the rectum and anal sphincters to relax, allowing feces to be expelled from the body.