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Detecation

GASTROINTESTINAL PHYSIOLOGY

Certam physiologic. events, as arising (orthocołir reflex) and ingestion ot food (jjastiocolic and gastroileal ri>flexes|, may initiate a mass penstalsis propellmg fecal bolus into rectum

Stimulabon of rcctal strctch — receptors sends afferent impulses to spinał cord (for local reflexest and thencc to brain (tor awareness ot urge)

"Awareness" of urge, correłated with visual and auditory srimtili, plus memorv and habit cause individual lo seek oul toilet and make other appropriate preparations and simultanęously cause

Local autonomie reflexes (via pełvk: s(>tanchnif nervesl cause rontraction of rertal musculature and retaxation of internal sphincter in effort lo expel feces    .

Pełvic spłanchmr ncrves

Pudendal and levator ani nerves

Voluntary rontraction of extomal sphinctor and levator ani musdes (v»a pudendal and levator ani nerves> to retain feces until suitable conditions prevail

ani muscle Internal

Extemal

sphincter

Ątf

• lló(V

Figurę 7.23 Defecation_

~Vfecation involves heeding the rectosphincteric reflex and relax-łtion of both the involuntary internal anal sphincter (innervated by ne pelvic splanchnic nerves of the parasympathetic division of the

autonomie nervous system) and voluntary external anal sphincter łinnervated by the somatic pudendal nerve). Contraction of the distal colon and rectum expels the feces.

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