Elimination Of Faeces

Question 1

What type of muscle is the Internal anal sphincter?

Answer 1

Smooth

Controlled by autonomic NS (involuntary)

Question 2

What type of muscle is the external anal sphincter?

Answer 2

Skeletal (striated)

Controlled by the Somatic NS (voluntary)

Question 3

What is the process of defaecate?

Answer 3

Slow peristaltic waves gently move faeces mass along length of bowel

Periodically, they become mass peristaltic waves, propelling faeces into rectum giving sense of fullness and need to defaecate

Question 4

What is rectal distension?

Answer 4

Leads to relaxation of internal anal sphincter

Allows contents of rectum to descend to upper part of anus

Question 5

What are the sequence of events in normal defecation?

Answer 5

1) mass peristaltic waves advance stool through colon to rectum
2) recto-anal inhibitory reflex causes internal anal sphincter to relax
3) external anal sphincter and puborectalis muscle contract until convenient to pass stool
4) when convenient, EAS and puborectalis relaxes
5) contraction of levator ani and abdominal muscles causes downward pressure and stool is expelled by muscles of the sigmoid colon and rectum