defectaion reflex

[harv1212]

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having a hard time finding this online (even with wiki lol!)

I know that the internal anal sphincter is para and the external is somatic innervation ...

when you def does your int. anal sphincter relax and your external contract??

why does damage to your int. anal sphincter cause fecal incontinence if it normally is under parasymp involuntary control???

if someone could clear this mess up (haha pun intended) I'd really appreciate it!

 

[norealname]

The parasympathetic defecation and Intrinsic myenteric reflexes are responsible for the relaxation of the internal anal sphincter and mass peristalsis when the rectum and sigmoid colon become distended due to fecal content. This will cause fecal matter to move down and produce the feeling of urgency. Under voluntary control, the external anal sphincter, which is normally constricted, relaxes and the person defecates.

When the internal anal sphincter is damaged, it will be abnormally relaxed, unable to hold fecal matter up in the rectum. This will cause feces to move down, pressing up against the contracted external anal sphincter. If enough feces accumulate, little droplets will be able to leak through the sphincter, producing a type of 'passive incontinence'. This passive incontinence can also happen when the person is doing some activity which increases their intra-abdominal pressure. Hope this is a fair explanation 🙂

 

[turkeyjerky]

also, there's the gastrocolic reflex, where distension of the stomach stimulates colonic motility and results the the urge to defecate. That's why you go poop after you eat breakfast.

 

[doc29]

motor impulses travel with S2-S4 parasympathetic(pelvic splanchnic neves) increases peristalsis and relax internal anal sphincter. if external anal sphincter is relaxed, defecation occurs with the help of contraction of ant.abdominal wall muscles and closure of glottis.
if external anal sphincter is contracted by pudendal nerve, defecation wont occur and feces will go back to sigmoid colon for storage.
Hypogastric plexus and lumbar splanchic nerves(sympathetic) decrease peristalsis and keep the tone of internal anal sphincter.
I hope it helps 🙂