Colon Diseases

Published on 16/04/2015 by admin

Filed under Surgery

Last modified 16/04/2015

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9 Colon Diseases

Anatomy of the Colon

image

Viscera: Mucosa and Musculature of Large Intestine

Parts and Landmarks

• Cecum, appendix, and ascending, transverse, descending, and sigmoid colon ~150 cm total length
• Cecum has the largest diameter: with obstruction, this is the most likely location for a perforation (greatest increase in pressure, per Laplace’s law).
• Colon externally distinguished by omental (epiploic) appendices, haustra (sacculations), and taeniae coli (triple bands of longitudinal smooth muscle)
• Only transverse and sigmoid portions typically have mesenteries.
• Greater omentum is fused to the transverse mesocolon and may be carefully separated surgically.
• Inferior ascending colon can have a mesentery (~10%) and is very mobile (risk for volvulus).
• See also appendix and anorectal topics.

Microscopic Anatomy

• Mucosa

image Epithelium: enterocytes (absorptive), goblet cells
image Lamina propria
image Muscularis mucosa

• Submucosa: strongest layer (connective tissue); Meissner’s plexus (neuronal network)
• Muscularis

image Auerbach’s plexus: myenteric neurons
image Inner circular muscle
image Outer longitudinal layer reduced to 3 bands: taeniae coli

image Mesocolic: posterior, attached to sigmoid and transverse mesocolon
image Omental: to which the epiploic appendages (appendices) are attached
image Free: with no omental or mesenteric attachments
image The taeniae merge into a continuous layer in the appendix and the rectum.

• Serosa: peritoneum
• Haustra: sacculations of the wall between the taeniae

Embryology

• From the cecum to the splenic flexure of the transverse colon, the colon was derived from the caudal midgut and is supplied by the superior mesenteric artery and vagus.
• From the descending colon through rectum, the colon was derived from hindgut and is supplied by the inferior mesenteric artery and sacral parasympathetics.

Innervation

Parasympathetic

• Preganglionic fibers

image Vagus: innervate colon from ileocecal junction to splenic flexure
image Pelvic splanchnic nerves (S2-S4): innervate descending and sigmoid colon

• Postganglionic fibers

image Meissner’s plexus: inner submucosal layer contains parasympathetic ganglion cells
image Auerbach’s plexus: outer, myenteric, contains parasympathetic ganglion cells

Sympathetic

• Preganglionic fibers distributed via splanchnic nerves to superior and inferior mesenteric plexuses
• Postganglionic fibers from cells in the following

image Superior mesenteric ganglion to the ascending and transverse colon via superior mesenteric plexus
image Inferior mesenteric ganglion to the descending and sigmoid colon via inferior mesenteric plexus

Sensory Fibers

• Vagal afferents from ascending and transverse colon
• Segmental visceral afferents for ascending and transverse colon travel parallel to sympathetics through the superior mesenteric plexuses and splanchnic nerves.
• Descending and sigmoid colon send visceral afferents through the inferior mesenteric, hypogastric, and pelvic plexuses.

Vessels and Lymphatics

image

Arteries of Large Intestine

Arterial Supply

• Superior mesenteric artery branches

image Ileocolic artery (with appendicular branch)
image Right colic artery
image Middle colic artery

• Inferior mesenteric artery branches

image Left colic artery (retroperitoneal)
image Sigmoid arteries (3 or 4)
image Superior rectal artery

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