Sigmoido-rectal junction reflex: role in the defecation mechanism

Area of Science:

• Gastroenterology
• Colorectal Physiology
• Anorectal Function

Background:

• The existence and function of a sphincter at the rectosigmoid junction (RSJ) remain debated.
• Understanding RSJ function is crucial for comprehending sigmoid colon storage and rectal evacuation mechanisms.

Purpose of the Study:

• To investigate the presence and functional role of a sphincter at the rectosigmoid junction (RSJ).
• To elucidate the mechanisms of sigmoid colon storage and rectal evacuation in healthy volunteers.

Main Methods:

• Studied pressure responses in the sigmoid colon, RSJ, and rectum during sigmoid and rectal distension in 18 healthy volunteers.
• Utilized balloon distension and station pull-through techniques to assess pressure changes and RSJ length.
• Evaluated pressure responses before and after anesthetizing the sigmoid colon or rectum to determine reflex pathways.

Main Results:

• Sigmoid distension caused increased sigmoid pressure, decreased RSJ pressure, and expulsion into the rectum.
• Rectal distension led to increased rectal and RSJ pressure.
• A high-pressure zone of 3.8 cm was identified at the RSJ, suggesting a functional sphincter.
• Anesthetizing either segment abolished RSJ pressure changes, indicating reflex control.

Conclusions:

• The rectosigmoid junction (RSJ) acts as a functional sphincter, opening via a 'rectosigmoid inhibitory reflex' during sigmoid contraction.
• The RSJ closes via a 'rectosigmoid excitatory reflex' during rectal contraction, preventing stool reflux.
• These reflexes facilitate efficient fecal storage in the sigmoid colon and controlled rectal evacuation.