The defecation reflex
a. is initiated when mass movements force fecal material into the rectum, stimulating stretch receptors in the rectal wall.
b. involves relaxation of the internal anal sphincter and contraction of the sigmoid colon and rectum.
c. can be overridden by voluntary contraction of the external anal sphincter.
d. both (a) and (b) above.
e. all of these answers.
E
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