NERVES OF

RECTUM

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RD

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STRUCTURE OF RECTUM

• (latin – rectus-straight)

• Sigmoid to anal canal

• Lies against lower 3 sacral vertebrae & coccyx, median sacral vessels

• Inferior sympathetic trunk & sacral plexus

FUNCTION OF RECTUM

• The rectum intestinum acts as a temporary storage site for feces. As the rectal walls expand due to the materials filling it from within, stretch receptors from the nervous system located in the rectal walls stimulate the desire to defecate. If the urge is not acted upon, the material in the rectum is often returned to the colon where more water is absorbed. If defecation is delayed for a prolonged period, constipation and hardened feces results.

• When the rectum becomes full, the increase in intrarectal pressure forces the walls of the anal canal apart, allowing the fecal matter to enter the canal. The rectum shortens as material is forced into the anal canal and peristaltic waves propel the feces out of the rectum. The internal and external sphincter allow the feces to be passed by muscles pulling the anus up over the exiting feces.

INNERVATION OF RECTUM

• Emptying of the rectum is analogous to emptying of the bladder in many respects

• Filling of the rectum activates stretch receptors in the rectal wall, which transmit impulses by the way of the inferior hypogastric plexus to segments S2 through S4 of the sacral spinal cord.

• Afferent impulses then ascend the spinal cord to higher control centers, which are probably located in the pintine reticular formation and the cerebral cortex.

• Rectal peristalsis is induced parasympathetic activation from segments S2 through S4, which also induces relaxation of internal sphincter.

• The sympathetic nervous system inhibits peristalsis.

• The external sphincter consists of striated muscle and is under voluntary control

• Rectal emptying is mainly accomplished voluntarily by abdominal pressing

• Below ‘pelvic pain line’

• Sympathetic – lumbar spinal cord via lumbar splanchnic nerves

• Parasympathetic – S2- S4 spinal cord level via pelvic splanchnic veins

• Pain afferents through parasympathetic to S2 – S4

RECTAL DISORDERS

• Fecal Retention: Transection of the spinal cord above the lumbosacral centers for defecation leads to fecal retention. Interruption of the afferent arm of those reflex pathway fro defecation deprives higher centers of information about the filling state of the rectum, while interruption of descending motor fibres impairs voluntary abdominal pressing. Sphincter closure is often inadequate because of spastic weakness

• Fecal Incontinence: Lesions of the sacral spinal cord (S2-S4) abolish the anal reflex and produce fecal incontinence. If the stool is watery, involuntary loss of stool occurs.