During the procedure of sigmoidoscopy, if the rectum is inflated with gas, increased peristalsis is seen in
A. Whole colon
B. Proximal colon
C. Distal colon
D. Whole intestine
ANS. C. Distal colon;
Explanation: The proximal colon is innervated by the
vagus; The distal colon receives its parasympathetic innervations from the
pelvic splanchnic nerves S234; via the hypogastric plexus; The parasympathetic
nerves cause contraction of the colonic musculature; Distension of the rectum
by feces or gases stimulates muscle receptors in the rectal wall; It will
provoke afferent impulse discharge via pelvic nerves; This will induce reflex
parasympathetic discharges over the pelvic splanchnic nerves; Since these
nerves innervate the distal colon, increased contractile activity will be seen
in the distal colon.
