Colon

The colon is the part of the large intestine from the cecum to the rectum

The colon in dogs is located within the abdominal cavity and is continuous with the cecum at the cecocolic junction. It terminates at the rectum, just before the pelvic inlet.

It consists of three main parts:

• Ascending colon: Short segment that runs cranially from the cecum.

• Transverse colon: Crosses from right to left, cranial to the root of the mesentery.

• Descending colon: Runs caudally along the left abdomen, transitioning into the rectum.

2. Histological Structure

• Mucosa: Smooth with no villi, contains crypts of Lieberkühn and numerous goblet cells that produce mucus.

• Submucosa: Contains vascular and lymphatic structures.

• Muscularis externa:

  • Inner circular layer.

  • Outer longitudinal layer, relatively uniform (lacks teniae coli as in horses).

• Serosa: Covers the colon except where it becomes retroperitoneal (descending colon).

3. Blood Supply

• Cranial mesenteric artery:

  • Supplies the ascending and transverse colon via the middle colic artery.

• Caudal mesenteric artery:

  • Supplies the descending colon via the left colic artery.

Venous drainage mirrors the arterial supply and empties into the portal venous system.

4. Lymphatic Drainage

• Through colic lymph nodes, eventually reaching the mesenteric lymph nodes.

5. Nervous Supply

• Parasympathetic:

  • Ascending and transverse colon via the vagus nerve.

  • Descending colon via the pelvic nerve.

• Sympathetic:

  • Through the lumbar splanchnic nerves, affecting motility and secretion.

6. Functional Aspects

• Absorption: Primarily water and electrolytes.

• Mucus secretion: Facilitates lubrication for fecal passage.

• Fecal storage: Temporary storage before defecation.

• Minimal microbial fermentation: Unlike herbivores, dogs have limited fermentation capacity due to their carnivorous diet.