Editing Fecal incontinence (section)

=== Anal sphincter weakness ===
The anal canal presents the final barrier to continence. The resting tone of the anal canal is not the only important factor; both the length of the high-pressure zone and its radial translation of force are required for continence. This means that even with normal anal canal pressure, focal defects such as the [[Keyhole defect|keyhole deformity]] can be the cause of substantial symptoms. [[External anal sphincter]] (EAS) dysfunction is associated with impaired voluntary control, whereas [[internal anal sphincter]] (IAS) dysfunction is associated with impaired fine-tuning of fecal control.<ref name="ASCRS core subjects FI" /> Defects of the external anal sphincter are associated with urge incontinence.<ref name="Desprez2021">{{cite journal |last1=Desprez |first1=C |last2=Turmel |first2=N |last3=Chesnel |first3=C |last4=Mistry |first4=P |last5=Tamiatto |first5=M |last6=Haddad |first6=R |last7=Le Breton |first7=F |last8=Leroi |first8=AM |last9=Hentzen |first9=C |last10=Amarenco |first10=G |title=Comparison of clinical and paraclinical characteristics of patients with urge, mixed, and passive fecal incontinence: a systematic literature review. |journal=International Journal of Colorectal Disease |date=April 2021 |volume=36 |issue=4 |pages=633–644 |doi=10.1007/s00384-020-03803-8 |pmid=33210162}}</ref> The external anal sphincter is supplied by the pudendal nerve. Damage to the nerve supply of the external anal sphincter on one side may not result in severe symptoms because there is substantial overlap in innervation by the nerves on the other side.<ref name="ASCRS textbook" /><!-- page 5 --> The internal anal sphincter receives extrinsic autonomic innervation via the [[inferior hypogastric plexus]], with sympathetic innervation derived from spinal levels L1-L2, and parasympathetic innervation derived from S2-S4.<ref name=":224" >{{Cite book |last=Standring |first=Susan |url=https://www.worldcat.org/oclc/1201341621 |title=Gray's Anatomy: The Anatomical Basis of Clinical Practice |year=1201 |isbn=978-0-7020-7707-4 |edition=42th |location=New York |pages=683 |oclc=1201341621}}</ref> Disruption of the function of the internal anal sphincter results in reduced resting pressure in the anal canal. This is associated with passive leakage.<ref name="Desprez2021" />

[[Lesion]]s which mechanically interfere with, or prevent the complete closure of the anal canal can cause a liquid stool or mucous [[rectal discharge]]. Such lesions include [[Hemorrhoid|piles]] (inflamed hemorrhoids), [[anal fissure]]s, [[anal cancer]], or fistulae.<ref name="ASCRS textbook" />

Nontraumatic conditions causing anal sphincter weakness include [[scleroderma]], damage to the [[pudendal nerve]]s, and IAS degeneration of unknown cause.<ref name="Yamada textbook" />