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SIGMOID COLON, RECTUM: EXTENT MESENTERY AND INNERVATION; ANAL CANAL

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Mesosigmoid membrane:
o Lane’s first and last kink
o Thickening and shortening of the peritoneum
of the left Iliac fossa
o Binds the junction of the Iliac and Pelvic colon
to the pelvic brim
o Avascular

Lecture Notes By: John Lorenz Beleno, RM, RN, MD

Sigmoid Colon:
• Lies between the Descending colon and the Rectum
• Begins at the pelvic brim and ends at the Rectosigmoid junction
• S3: where peritoneal investment and mesentery of
the Sigmoid ceases
• Length: 25-40 cm (10-15 inches)
o Varies depending on the length of the Mesosigmoid
• Anatomic landmark:
o External Iliac artery: divides the Sigmoid colon into Iliac and Pelvic divisions
• Divisions:
o Iliac Segment:
▪ Lies in the Iliac fossa
▪ Extends to the pelvic brim
o Pelvic Segment:
▪ Omega-shaped coil (Ω)
▪ Suspended from the posterior pelvic wall
by the Pelvic Mesocolon
▪ Located at the pelvic cavity
▪ Lateral limb:
• Part of the pelvic colon that is mobile
• Mobility depends on the size of the
mesocolon
▪ Medial limb:
• Attached to the root of the mesocolon
• Intersigmoid Recess:
o Small funnel-shaped pouch
o Deep or superficial
o Usually located towards the root
of the mesocolon
o Acts as a guide to the Left Ureter

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Clinical:
o Internal or Intra-Peritoneal Hernia:
▪ Part of the bowel, specially the distal part
of the small intestines, insinuates through
the intersigmoid recess and gets trapped
in the recess
o Volvulus:
▪ Obstruction caused by twisting of the
stomach or intestines upon itself
▪ Contents get accumulated in the area creating a “Closed-loop” obstruction
▪ Affects the blood supply to the affected intestines
▪ Will eventually burst leading to Peritonitis
▪ Peritonitis can lead to Sepsis then death

Rectosigmoid Junction:
• Termination of the Sigmoid colon
• Features:
o Narrowing of the diameter of the colon
o Lack of peritoneal investment
o Disappearance of a true mesentery below the
rectosigmoid
o Spreading out of 3 longitudinal Taenia coli
o Appendices Epiploicae up to its end
▪ Fatty tissues hanging at the wall of
the large intestines
o Gross morphologic change internally
Rectum:
• Length: 13 cm
• Begins in front of S3
• Course:
o Passes downwards following the curve of the
Sacrum and the Coccyx
o Ends one inch in front of the tip of the Coccyx
• Rectal Ampulla:
o Dilated portion of the Rectum where the fecal
material is usually stored
• Peritoneal Covering:
o Upper third: anterior and lateral peritoneum
o Middle third: anterior surface
o Lower third: devoid of peritoneal covering
Jlb_MD

Dr
...
John Lorenz Beleno

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Muscular coat:
o Outer longitudinal
o Inner circular
Taenia Coli: 3 come together forming a broad band
Rectal valves:
o Superior Rectal valve
o Middle Rectal valve
o Inferior Rectal valve
o Left-Right-Left positions

ANATOMY

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2
Jlb_MD

SIGMOID COLON, RECTUM: EXTENT MESENTERY AND INNERVATION; ANAL CANAL
ANATOMY

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Anal gland:
o Crypts of the anal gland
▪ Prone to infection
o Perianal abscess:
▪ Usually starts at the anal mucosa going
through the subcutaneous layer
▪ When it ruptures there will be a fistula
(communication) between the perianal (external) opening and the anal canal (internal

DR

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