Colon Diseases

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

• Marginal artery anastomoses between the superior and inferior mesenteric arteries

Related posts:

  1. Uterus and Adnexal Diseases
  2. Prostate Diseases
  3. Small Intestine Diseases
  4. Ankle and Foot Fractures

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Aug 12, 2016 | Posted by in ANATOMY | Comments Off on Colon Diseases

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